BDT Java-2 Sprint Summary

Modified on Fri, 10 Nov, 2023 at 3:57 PM

Java-2

Sprint Summary for Java-2

Index:

Four Pillars of OOPS
Encapsulation
Inheritance
Abstraction
Polymorphism
Gradle
Unit Testing
Exception Handling
Object Class Methods

Topic 1: Pillars of OOPs

Four Pillars of OOPS

The Four Pillars of Object-Oriented Programming (OOP) in Java are:

Encapsulation: It is the bundling of data and methods into a single unit called a class. Encapsulation ensures data security by restricting access to the internal state of an object. Private variables are used to encapsulate data, and public getter and setter methods provide controlled access. Constructors initialize object state, and complex implementation details are hidden.

Inheritance: It enables a class to inherit properties and behaviors from another class. Inheritance promotes code reuse and establishes a "is-a" relationship between classes. The extends keyword is used to derive a class from a base class. Methods and variables are inherited, and overridden methods provide specific implementations. The super keyword is used to access superclass members.

Polymorphism: It allows an object to take on different forms. Polymorphism is achieved through method overriding and interface implementation. It enables dynamic method dispatch, where the appropriate method is invoked based on the actual object at runtime. Polymorphism promotes code extensibility and flexibility.

Abstraction: It involves representing complex real-world entities as simplified models. Abstraction is achieved through abstract classes and interfaces. Abstract classes provide a blueprint with abstract and concrete methods, while interfaces define a contract with abstract methods. Concrete classes implement interfaces or extend abstract classes to provide specific implementations. Abstraction hides unnecessary details and focuses on essential features.

Best Practices:
Encapsulation: Hide implementation details and provide controlled access.
Inheritance: Promote code reuse and create class hierarchies.
Polymorphism: Enable dynamic method dispatch and interface implementation.
Abstraction: Focus on essential features, create contracts, and provide flexibility.

In summary, encapsulation ensures data security, inheritance promotes code reuse, polymorphism allows objects to take on different forms, and abstraction simplifies complex entities. Applying these principles enhances code organization, flexibility, and maintainability.

Topic 2: Encapsulation

Encapsulation

Encapsulation in Java is the bundling of data and methods into a single unit called a class, where the data is hidden and accessed only through controlled methods.

Where is it used?
Encapsulation is widely used in Java programming to achieve data security and abstraction.
It is applied in scenarios where you want to restrict direct access to class variables and ensure data integrity.

How is it used?
Declare class variables as private to encapsulate data and prevent direct access from outside the class.
Provide public getter and setter methods to access and modify the private variables.
Use constructors to initialize the object's state.
Implement additional methods for performing specific operations on the data.

Example:

public class Person {
    private String name;
    private int age;

    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }


    public String getName() {
        return name;
    }
    
    public int getAge() {
        return age;
    }

    public void setName(String name) {
        this.name = name;
    }

    public void setAge(int age) {
        this.age = age;
    }
}

public class Main {
    public static void main(String[] args) {
        Person person = new Person("John", 25);
        System.out.println(person.getName()); // Output: John

        person.setAge(30);
        System.out.println(person.getAge()); // Output: 30
    }
}

In the example, the Person class encapsulates the name and age variables as private. The getter and setter methods provide controlled access to these variables. By using the public methods, we can retrieve and modify the person's name and age.

Takeaways / Best Practices:

Encapsulate data by making variables private.
Use public getter and setter methods to access and modify the data.
Validate input parameters within setter methods to maintain data integrity.
Hide complex implementation details within the class, providing a simple and consistent interface to interact with the object.
Encapsulation enhances code maintainability, security, and flexibility.

Getters and Setters

Getters and setters in Java are methods used to access and modify the values of private variables in a class, providing controlled access to the class's data.

Where is it used?
Getters and setters are commonly used in object-oriented programming to enforce encapsulation and ensure data integrity.
They are used when you want to restrict direct access to class variables and provide controlled access points.

How is it used?
Declare private instance variables in a class.
Create public getter methods to retrieve the values of the private variables.
Create public setter methods to modify the values of the private variables.
In the getter methods, return the value of the corresponding private variable.
In the setter methods, validate the input and assign the value to the corresponding private variable.

Example:

public class Person {
private String name;
private int age;

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public int getAge() {
return age;
}

public void setAge(int age) {
if (age >= 0) {
this.age = age;
} else {
System.out.println("Invalid age!");
}
}
}

public class Main {
public static void main(String[] args) {
Person person = new Person();
person.setName("John");
person.setAge(25);

System.out.println(person.getName()); // Output: John
        System.out.println(person.getAge()); // Output: 25


person.setAge(-5); // Invalid age!
}
}

In the example, the Person class has private variables name and age. The getter methods (getName and getAge) retrieve the values of these variables, and the setter methods (setName and setAge) modify the values after performing validation checks.

Takeaways / Best Practices:

Getters and setters provide controlled access to class variables, ensuring data integrity.
Use meaningful names for getter and setter methods to enhance code readability.
Validate input parameters in setter methods to maintain data consistency.
Getters and setters allow flexibility to add additional logic or transformations in the future without changing the class's interface.
It is a good practice to follow the JavaBeans naming convention for getter and setter methods.

Topic 3: Inheritance

Inheritance

Inheritance in Java is a mechanism that allows a class to inherit properties and behaviors from another class, enabling code reuse and creating a hierarchical relationship between classes.

Where is it used?
Inheritance is used when you want to create a new class (child class) based on an existing class (parent class) to inherit its properties and behaviors.
It is used to establish an "is-a" relationship between classes, where the child class is a specialized version of the parent class.

How is it used?
Create a parent class (superclass) with common properties and behaviors.
Create a child class (subclass) that extends the parent class using the extends keyword.
The child class inherits the properties and behaviors of the parent class.
The child class can also have its unique properties and behaviors in addition to what it inherits.
Access the inherited properties and behaviors using the dot notation or super keyword.

Example:

class Animal {
    protected String name;

    public Animal(String name) {
        this.name = name;
    }


    public void sound() {
        System.out.println("Animal makes a sound.");
    }
}

class Dog extends Animal {
    private String breed;
   
    public Dog(String name, String breed) {
        super(name);
        this.breed = breed;
    }

    public void bark() {
        System.out.println("Dog barks!");
    }
}

public class Main {
    public static void main(String[] args) {
        Dog dog = new Dog("Buddy", "Labrador");
        System.out.println(dog.name); // Output: Buddy
        dog.sound(); // Output: Animal makes a sound.
        dog.bark(); // Output: Dog barks!
    }
}

In the example, the Animal class is the parent class with a name property and a sound method. The Dog class is the child class that extends Animal. It adds a breed property and a bark method. The child class inherits the name property and sound method from the parent class using the super keyword.

Takeaways / Best Practices:

Inheritance promotes code reuse and modularity.
Use inheritance when there is an "is-a" relationship between classes, where the child class can be considered a specialized version of the parent class.
In Java, a class can only inherit from a single class (single inheritance). However, it can implement multiple interfaces (multiple inheritance through interfaces).
Be mindful of the access modifiers (public, protected, private) when designing parent and child classes.
Avoid deep inheritance hierarchies as they can make the code complex and harder to maintain. Favor composition over deep inheritance.
Carefully consider the design and relationships between classes to ensure a proper inheritance hierarchy.

Final Method

A final method in Java is a method that cannot be overridden by subclasses, providing a way to enforce immutability and prevent method overriding.

Where is it used?
Final methods are used when you want to prevent subclasses from modifying or overriding a specific method in a class.
It is commonly used in class hierarchies where certain methods need to retain their functionality without being altered in subclasses.

How is it used?
Declare a method with the final keyword in the class where you want to prevent method overriding.
The final method cannot be overridden by any subclass.
If a subclass attempts to override a final method, it will result in a compilation error.

Example:

class Vehicle {
public final void start() {
System.out.println("Vehicle started.");
}
}

class Car extends Vehicle {
// Trying to override the final method will result in a compilation error
/*public void start() {
System.out.println("Car started.");
}*/
}

public class Main {
public static void main(String[] args) {
Vehicle vehicle = new Vehicle();
        vehicle.start(); // Output: Vehicle started.


        Car car = new Car();
        car.start(); // Output: Vehicle started.
    }
}

In the example, the Vehicle class has a final method start(). The Car class attempts to override the start() method, but since it is declared as final, it results in a compilation error.

Takeaways / Best Practices:

Use final methods when you want to prevent method overriding and ensure that the behavior of a method remains unchanged in subclasses.
Final methods promote code stability and prevent accidental modifications in subclass implementations.
Final methods are useful in frameworks or libraries where specific behaviors need to be retained and not altered by subclasses.
Be mindful of the design and functionality of your classes when using final methods.
Ensure that the decision to make a method final aligns with the overall class hierarchy and inheritance structure.
It is important to document and communicate the usage of final methods to other developers working on the codebase.

Final Class

A final class in Java is a class that cannot be extended or subclassed, providing a way to prevent inheritance and ensure that the class implementation remains unchanged.

Where is it used?
Final classes are used when you want to restrict the extension of a class to maintain its integrity and prevent modifications through inheritance.
It is commonly used in utility classes, where the class provides a set of static methods and does not need to be extended.

How is it used?
Declare a class with the final keyword to make it a final class.
A final class cannot be extended by any other class.
If a subclass tries to extend a final class, it will result in a compilation error.

Example:

final class MathUtils {
    public static int add(int a, int b) {
        return a + b;
    }
}


// Trying to extend a final class will result in a compilation error
/*class AdvancedMathUtils extends MathUtils {
    // ...
}*/

public class Main {
    public static void main(String[] args) {
        int sum = MathUtils.add(5, 3);
        System.out.println("Sum: " + sum); // Output: Sum: 8
    }
}

In the example, the MathUtils class is declared as final, and it provides a static method add() for performing addition. The AdvancedMathUtils class attempts to extend the final class MathUtils, which results in a compilation error.

Takeaways / Best Practices:

Use final classes when you want to prevent inheritance and ensure that the class implementation remains unchanged.
Final classes provide a way to enforce encapsulation and protect the integrity of the class by preventing modifications through inheritance.
Final classes are often used for utility classes, where the class provides a set of static methods and does not need to be extended.
When designing APIs or frameworks, consider using final classes to provide a stable and unmodifiable implementation that cannot be overridden or extended by users.
Document the usage and purpose of final classes to communicate their intended behavior and to guide developers using the classes.
Be cautious when using final classes, as they limit flexibility and potential future enhancements through inheritance. Evaluate the design and requirements of your application to determine if the use of final classes is appropriate.

Keywords - final, extends, super

Keywords - final, extends, super have different functionalities in Java. Here's an explanation of each:

final:
What is it? Final is a keyword in Java used to declare that a variable, method, or class cannot be modified or overridden.

Where is it used? It can be used with variables, methods, and classes.

How is it used?
For variables: A final variable cannot be reassigned once initialized.
For methods: A final method cannot be overridden by subclasses

For classes: A final class cannot be subclassed.

Example:

final int MAX_VALUE = 100;
final void printMessage() {
    System.out.println("Hello, World!");
}

final class Shape {
    // Class implementation
}

Takeaways / Best Practices:

Use the final keyword for variables when you want to create constants that should not be modified.
Use the final keyword for methods when you want to prevent subclasses from overriding the method.
Use the final keyword for classes when you want to prevent the class from being subclassed.
Document the purpose and usage of final elements to communicate their intended immutability or non-overridability to other developers.
Be mindful of the impact of using final, as it restricts certain behaviors and flexibility in the code. Use it judiciously to maintain code integrity and prevent unintended modifications.

extends:

What is it? Extends is a keyword in Java used to establish inheritance between classes.

Where is it used? It is used in class declarations to indicate that a class is derived from another class.

How is it used?
Syntax: class ChildClass extends ParentClass
The child class inherits all the fields and methods from the parent class.
The child class can add additional fields and methods or override the inherited ones.

Example:

class Animal {
    void eat() {
        System.out.println("Animal is eating.");
    }
}

class Dog extends Animal {
    void bark() {
        System.out.println("Dog is barking.");
    }
}

public class Main {
    public static void main(String[] args) {
        Dog dog = new Dog();
        dog.eat(); // Output: Animal is eating.
        dog.bark(); // Output: Dog is barking.
    }
}

Takeaways / Best Practices:

Use extends keyword to establish an inheritance relationship between classes.
Inheritance allows code reuse and supports the concept of polymorphism.
Document the inheritance relationship between classes to provide a clear understanding of the class hierarchy to other developers.
Be mindful of the design and relationship between classes when using inheritance. Ensure that it follows the principles of object-oriented programming and promotes code reusability and maintainability.

super:

What is it? Super is a keyword in Java used to refer to the superclass or parent class.

Where is it used? It is used within a subclass to refer to the superclass and access its members.

How is it used?
Syntax: super.member
It can be used to call the superclass constructor or access superclass methods and fields.

Example:

class Vehicle {
    void display() {
        System.out.println("This is a vehicle.");
    }
}

class Car extends Vehicle {
    @Override
    void display() {
        super.display(); // Calls the display() method of the superclass
        System.out.println("This is a car.");
    }
}

public class Main {
    public static void main(String[] args) {
        Car car = new Car();
        car.display();
    }
}

Takeaways / Best Practices:

Use super keyword to access members of the superclass from the subclass.
Super is commonly used when overriding methods in the subclass to call the corresponding method in the superclass.
Document the usage of super keyword in the code to explain the rationale behind accessing superclass members.
Be cautious when using super, as it may introduce tight coupling between classes. Ensure that the superclass and subclass have a clear and logical relationship to maintain code organization and readability.

Protected - Access Specifier

Protected is an access specifier in Java that allows members (variables, methods, and constructors) to be accessed within the same package or by subclasses in different packages.

What is it? Protected is an access specifier that provides a limited scope of accessibility for class members.

Where is it used? It is used to control the visibility and accessibility of class members.

How is it used?
Protected members can be accessed within the same package by any class.
Protected members can be accessed in subclasses, even if they are in a different package.
Protected members are not accessible outside the package unless they are accessed through inheritance in a subclass.

Example:

package com.example;

public class ParentClass {
  protected int protectedField;

  protected void protectedMethod() {
      System.out.println("This is a protected method.");
  }
}

package com.example.subpackage;
import com.example.ParentClass;

public class ChildClass extends ParentClass {
  public void accessProtectedMember() {
    protectedField = 10; // Accessing protected field from the subclass
    protectedMethod(); // Accessing protected method from the subclass
  }
}

Takeaways / Best Practices:

Use protected access specifier when you want to provide access to class members within the same package and in subclasses.
Document the usage and rationale behind using protected access specifier to guide other developers on the intended visibility of class members.
Be cautious when using protected, as it grants access to members that may affect encapsulation and data integrity. Ensure that the use of protected aligns with the design and requirements of the class hierarchy.
Follow good coding practices by keeping the visibility of class members as restricted as possible to maintain encapsulation and minimize dependencies.

Topic 4: Abstraction

Abstraction

Abstraction is a concept in Java that focuses on hiding unnecessary details and exposing only essential features to the user.

What is it?

Abstraction is a way of simplifying complex systems by focusing on the essential aspects and hiding unnecessary details.

Where is it used?

It is used in situations where you want to provide a simplified view of a system or when you want to define a common interface for a group of related classes.

How is it used?
Abstraction is achieved in Java through abstract classes and interfaces.
Abstract classes define common properties and behaviors that can be shared by multiple subclasses. They can have both abstract and non-abstract methods.
Interfaces provide a contract for classes to implement, defining a set of methods that must be implemented. Interfaces cannot have method implementations.
By utilizing abstract classes and interfaces, you can define a common structure or behavior that can be inherited or implemented by different classes.

Example:

// Abstract class
abstract class Shape {
    protected String color;

    public Shape(String color) {
        this.color = color;
    }

    abstract double getArea();
    public void display() {
        System.out.println("This is a " + color + " shape.");
    }
}

// Concrete subclass
class Circle extends Shape {
    private double radius;

    public Circle(String color, double radius) {
        super(color);
        this.radius = radius;
    }

    @Override
    double getArea() {
        return Math.PI * radius * radius;
    }
}

// Interface
interface Drawable {
    void draw();
}

// Class implementing the interface
class Rectangle implements Drawable {
    public void draw() {
        System.out.println("Drawing a rectangle...");
    }
}

Takeaways / Best Practices:

Use abstraction to define common properties, behaviors, or contracts that can be shared by multiple classes.
Abstract classes should be used when you want to provide a partial implementation along with abstract methods that must be implemented by subclasses.
Interfaces should be used when you want to define a contract that classes must adhere to. They provide a way to achieve multiple inheritances of behavior.
Carefully design and document the abstract classes and interfaces to ensure clarity and ease of use for other developers.
Follow naming conventions and use descriptive names for abstract classes and interfaces to make their purpose and functionality clear.

Abstract Classes

Abstract classes in Java are classes that cannot be instantiated and serve as a blueprint for creating concrete subclasses.

What is it?

Abstract classes are classes that cannot be instantiated and provide a partial or incomplete implementation of a class.

Where is it used?

Abstract classes are used when you want to define common properties and behaviors that can be shared by multiple subclasses.

How is it used?
Abstract classes are declared using the abstract keyword in Java.
They can have both abstract and non-abstract methods.
Abstract methods are declared without an implementation and must be implemented by the concrete subclasses.
Abstract classes can also have concrete methods that provide a default implementation that can be inherited by the subclasses.
Abstract classes can have instance variables, constructors, and can be extended by other classes.

Example:

// Abstract class
abstract class Animal {
    protected String name;

    public Animal(String name) {
        this.name = name;
    }

    abstract void makeSound();


    public void eat() {
        System.out.println(name + " is eating.");
    }
}

// Concrete subclass
class Dog extends Animal {
    public Dog(String name) {
        super(name);
    }

    @Override
    void makeSound() {
        System.out.println("Dog barks!");
    }
}

// Concrete subclass
class Cat extends Animal {
    public Cat(String name) {
        super(name);
    }

    @Override
    void makeSound() {
        System.out.println("Cat meows!");
    }
}

Takeaways / Best Practices:

Use abstract classes when you want to define common properties and behaviors for a group of related classes.
Abstract classes should be used when you have some common implementation to be shared among multiple subclasses.
Abstract methods in the abstract class should be implemented by the concrete subclasses.
Abstract classes cannot be instantiated, so they are typically used as a superclass for creating concrete subclasses.
Abstract classes can have instance variables, constructors, and concrete methods.
Carefully design and document the abstract class to ensure clarity and ease of use for other developers.
Use abstract classes when you want to enforce a common structure and behavior in related classes.

Abstract Methods

Abstract methods in Java are methods declared in an abstract class or interface that do not have an implementation and must be overridden by the subclasses.

What is it?

Abstract methods are methods without an implementation, declared in an abstract class or interface.

Where is it used?

Abstract methods are used in abstract classes and interfaces to define a contract for subclasses to implement.

How is it used?
Abstract methods are declared using the abstract keyword and do not have a body.
They are intended to be overridden by the concrete subclasses to provide an implementation.
Abstract methods define the method signature (name, parameters, and return type) but leave the implementation details to the subclasses.
Subclasses that extend an abstract class or implement an interface with abstract methods must provide an implementation for all the abstract methods.
Abstract methods provide a way to enforce a specific behavior in subclasses while allowing them to have their own unique implementation.

Example:

abstract class Shape {
    abstract double calculateArea();
}

class Rectangle extends Shape {
    private double length;
    private double width;

    public Rectangle(double length, double width) {
        this.length = length;
        this.width = width;
    }

    @Override
    double calculateArea() {
        return length * width;
    }
}

class Circle extends Shape {
    private double radius;

    public Circle(double radius) {
        this.radius = radius;
    }

    @Override
    double calculateArea() {
        return Math.PI * radius * radius;
    }
}

Takeaways / Best Practices:

Abstract methods are used to define a contract for subclasses, ensuring that specific methods are implemented.
Abstract methods are declared in abstract classes or interfaces using the abstract keyword.
Abstract methods do not have an implementation and must be overridden by the concrete subclasses.
Subclasses inheriting from an abstract class or implementing an interface with abstract methods must provide an implementation for all the abstract methods.
Abstract methods define the method signature but leave the implementation details to the subclasses.
Abstract methods allow for polymorphism, where different subclasses can have different implementations of the same method.
Abstract methods provide a way to enforce a specific behavior or functionality across different classes while allowing customization in the subclasses.

Interfaces

Interfaces in Java define a contract for classes to implement, specifying a set of methods that must be provided by implementing classes.

What is it?

An interface is a reference type in Java that defines a contract for classes to implement, specifying a set of methods without an implementation.

Where is it used?

Interfaces are used to achieve abstraction and define common behavior that multiple classes can adhere to.

How is it used?

Interfaces are declared using the interface keyword and contain method signatures without any implementation details.

Classes implement interfaces by using the implements keyword in the class declaration and providing implementations for all the interface's methods.

A class can implement multiple interfaces, allowing it to inherit the methods and define the behavior specified by each interface.

Interface methods are implicitly public and abstract, so they must be implemented with the public access modifier in the implementing class.

Interfaces can also define constant fields (variables that are public, static, and final) that can be accessed by implementing classes.

Implementing an interface allows the class to be used in a polymorphic way, where instances of the class can be treated as instances of the interface.

Interfaces can extend other interfaces using the extends keyword, allowing for inheritance of method signatures.

Example:

interface Drawable {
    void draw();
}

class Circle implements Drawable {
    @Override
    public void draw() {
        System.out.println("Drawing a circle");
    }
}

class Rectangle implements Drawable {
    @Override
    public void draw() {
        System.out.println("Drawing a rectangle");
    }
}

class Main {
    public static void main(String[] args) {
        Drawable circle = new Circle();
        circle.draw();

        Drawable rectangle = new Rectangle();
        rectangle.draw();
    }
}

Takeaways / Best Practices:

Interfaces define a contract for classes to implement, specifying a set of methods without implementation details.
Classes implement interfaces using the implements keyword and provide implementations for all the interface's methods.
Interfaces allow for achieving abstraction and defining common behavior that multiple classes can adhere to.
A class can implement multiple interfaces, inheriting and providing implementations for the methods specified by each interface.
Interface methods are implicitly public and abstract, so they must be implemented with the public access modifier in the implementing class.
Interfaces can also define constant fields that can be accessed by implementing classes.
Implementing an interface allows the class to be used in a polymorphic way, treating instances of the class as instances of the interface.
Interfaces can extend other interfaces, allowing for inheritance of method signatures.
Using interfaces promotes loose coupling and flexibility in the design of Java applications.

Keywords - abstract, implements, interface

What is it?

abstract: A keyword used to declare an abstract class or method.

implements: A keyword used to specify that a class implements an interface.

interface: A keyword used to declare an interface.

Where is it used?
abstract: Used when creating abstract classes or methods that are meant to be extended or implemented by subclasses.

implements: Used in the class declaration to indicate that a class implements one or more interfaces.

interface: Used to define a contract of methods that implementing classes must adhere to.

How is it used?

abstract:
Abstract classes are declared using the abstract keyword, and they can have abstract methods (methods without implementations) and non-abstract methods.
Abstract methods are declared with the abstract keyword and do not have an implementation in the abstract class. Subclasses must provide an implementation for abstract methods.
Abstract classes cannot be instantiated, but they can be extended by subclasses, which provide concrete implementations for the abstract methods.

implements:
When a class implements an interface, it must provide implementations for all the methods declared in the interface.
The implements keyword is used in the class declaration, followed by the name of the interface(s) that the class implements.
Multiple interfaces can be implemented by separating them with commas.

interface:
Interfaces are declared using the interface keyword and define a contract of methods that implementing classes must implement.
Interface methods are declared without an implementation, only specifying the method signature.
Classes implementing an interface must provide implementations for all the methods declared in the interface.
Interfaces can also define constant fields (variables that are public, static, and final) that implementing classes can access.

Example:

// Abstract class example
abstract class Animal {
    public abstract void sound();
    public void sleep() {
        System.out.println("Animal is sleeping");
    }
}

// Interface example
interface Jumpable {
    void jump();
}

// Class implementing an interface
class Rabbit implements Jumpable {
    public void jump() {
        System.out.println("The rabbit is jumping");
    }
}

// Class extending an abstract class
class Cat extends Animal {
    public void sound() {
        System.out.println("The cat makes a sound");
    }
}

class Main {
    public static void main(String[] args) {
        Jumpable rabbit = new Rabbit();
        rabbit.jump();
        Animal cat = new Cat();
        cat.sound();
        cat.sleep();
    }
}

Takeaways / Best Practices:

The abstract keyword is used to declare abstract classes and abstract methods, which are meant to be extended or implemented by subclasses.
The implements keyword is used to indicate that a class implements one or more interfaces, and it must provide implementations for all the methods declared in the interface(s).
Interfaces define a contract of methods that implementing classes must adhere to, and they can also include constant fields.
Abstract classes cannot be instantiated, but they can be extended by subclasses, which provide concrete implementations for the abstract methods.
Using abstract classes and interfaces promotes code reusability, flexibility, and abstraction in Java applications.

Topic 5: Polymorphism

Polymorphism

What is it?
Polymorphism is the ability of an object to take on many forms. In Java, it refers to the ability of a reference variable to refer to objects of different types and have different behaviors based on the actual type of the object at runtime.

Where is it used?
Polymorphism is used in object-oriented programming to create flexible and extensible code. It allows different objects to be treated uniformly through their common interfaces or superclass references.

How is it used?
Polymorphism can be achieved in Java through the following steps:
Define a superclass or interface that declares common methods.
Create subclasses that inherit from the superclass or implement the interface.
Override the common methods in the subclasses to provide specific implementations.
Use the superclass reference or interface reference to refer to objects of different subclasses.
Invoke the common methods using the superclass or interface reference, and the specific implementations will be called based on the actual type of the object.

Example:

// Superclass
class Animal {
    public void makeSound() {
        System.out.println("Animal makes a sound");
    }
}

// Subclasses
class Dog extends Animal {
    public void makeSound() {
        System.out.println("Dog barks");
    }
}

class Cat extends Animal {
    public void makeSound() {
        System.out.println("Cat meows");
    }
}

class Main {
    public static void main(String[] args) {
        Animal animal1 = new Dog(); // Polymorphic reference
        Animal animal2 = new Cat(); // Polymorphic reference

        animal1.makeSound(); // Output: "Dog barks"
        animal2.makeSound(); // Output: "Cat meows”
    }
}

Takeaways / Best Practices:

Polymorphism allows for code flexibility and extensibility by treating objects of different types uniformly through common interfaces or superclass references.
It promotes code reusability and maintainability by leveraging inheritance and method overriding.
The actual behavior of a polymorphic object is determined at runtime based on its actual type.
Polymorphism is a fundamental concept in object-oriented programming and is widely used in Java applications to create flexible and modular code.

Types of Polymorphism

What is it?
Types of polymorphism in Java refer to the different ways in which polymorphism can be achieved: compile-time polymorphism (method overloading) and runtime polymorphism (method overriding).

Where is it used?
Types of polymorphism are used in Java to enable different forms of method invocation and provide flexibility in method implementations.

How is it used?

Method Overloading:
Define multiple methods in a class with the same name but different parameters (either different types or different number of parameters).

The compiler determines the appropriate method to call based on the method invocation, matching the method name and parameters.

Method overloading allows methods with similar functionality but different input variations to be grouped together.

Method Overriding:
Create a subclass that extends a superclass or implements an interface.

Override a method in the subclass by providing a new implementation that has the same signature (name, return type, and parameters) as the superclass method.

The method in the subclass is invoked when the method is called using a reference of the subclass type.

Method overriding allows for dynamic method dispatch, where the appropriate method to call is determined at runtime based on the actual object type.

Example:

// Method Overloading
class Calculator {
    public int add(int num1, int num2) {
        return num1 + num2;
    }

    public double add(double num1, double num2) {
        return num1 + num2;
    }
}

// Method Overriding
class Animal {
    public void makeSound() {
        System.out.println("Animal makes a sound");
    }
}

class Dog extends Animal {
    @Override
    public void makeSound() {
        System.out.println("Dog barks");
    }
}

class Main {
    public static void main(String[] args) {
        // Method Overloading
        Calculator calculator = new Calculator();
        int sum1 = calculator.add(2, 3); // Output: 5
        double sum2 = calculator.add(2.5, 3.7); // Output: 6.2

        // Method Overriding
        Animal animal = new Dog();
        animal.makeSound(); // Output: "Dog barks"
    }
}

Takeaways / Best Practices:

Method overloading allows for multiple methods with the same name but different parameters, providing flexibility in method invocation and improving code readability.
Method overriding enables the subclass to provide its own implementation of a method inherited from the superclass, allowing for polymorphic behavior and dynamic method dispatch.
Polymorphism, achieved through method overloading and overriding, enhances code reusability, flexibility, and extensibility.
Care should be taken to choose meaningful method names and maintain consistency in method signatures to avoid confusion and improve code maintainability.

Method Overloading

What is it?
Method overloading in Java refers to the ability to define multiple methods with the same name but different parameters in a class.

Where is it used?
Method overloading is used in Java to provide different ways of invoking methods with varying input parameters while maintaining the same method name.

How is it used?
Define multiple methods in a class with the same name but different parameters (either different types or different number of parameters).

The compiler determines the appropriate method to call based on the method invocation, matching the method name and parameters.

Method overloading allows methods with similar functionality but different input variations to be grouped together.

Example:

class Calculator {
    public int add(int num1, int num2) {
        return num1 + num2;
    }

    public double add(double num1, double num2) {
        return num1 + num2;
    }

    public int add(int num1, int num2, int num3) {
        return num1 + num2 + num3;
    }
}

class Main {
    public static void main(String[] args) {
        Calculator calculator = new Calculator();
        int sum1 = calculator.add(2, 3); // Invokes the first add method
        double sum2 = calculator.add(2.5, 3.7); // Invokes the second add method
        int sum3 = calculator.add(2, 3, 4); // Invokes the third add method


        System.out.println(sum1); // Output: 5
        System.out.println(sum2); // Output: 6.2
        System.out.println(sum3); // Output: 9
    }
}

Takeaways / Best Practices:

Method overloading allows you to define methods with the same name but different parameters, providing flexibility in method invocation.
Method overloading improves code readability by allowing developers to use the same method name for similar operations.
When overloading methods, ensure that the parameter types or the number of parameters differ to avoid ambiguity.
Method overloading is resolved at compile-time based on the method signature, so the return type or access modifiers do not affect method overloading.

Topic 18: Gradle

Gradle

What is it?
Gradle is a build automation tool and dependency management system that is used to automate the building, testing, and deployment of software projects.

Where is it used?
Gradle is commonly used in Java projects, as well as in other programming languages such as Kotlin and Groovy. It is widely adopted in the software development industry.

How is it used?
Install Gradle on your system.
Define a build.gradle file in the root directory of your project, which specifies the project configuration and build tasks.
Configure dependencies in the build.gradle file, specifying the required libraries and external dependencies for your project.
Define tasks in the build.gradle file to perform specific build actions, such as compiling code, running tests, generating documentation, etc.
Execute Gradle commands using the command line or an integrated development environment (IDE) to build, test, and deploy your project.

Example:

// build.gradle

// Specify the Java plugin
plugins {
    id 'java'
}

// Define project configuration
group 'com.example'
version '1.0'

// Configure dependencies
dependencies {
    implementation 'com.google.guava:guava:30.1-jre'
    testImplementation 'junit:junit:4.13.2'
}

// Define build tasks
tasks {
    compileJava {
        options.compilerArgs += ["--release", "8"]
    }


    test {
        useJUnitPlatform()
    }

    javadoc {
        options.addStringOption('Xdoclint:none', '-quiet')
    }
}

Takeaways / Best Practices:

Gradle provides a powerful and flexible build system for Java projects, allowing you to define and automate various build tasks.
It supports dependency management, making it easy to include external libraries and manage their versions.
Gradle uses a Groovy-based domain-specific language (DSL) for build configuration, which offers a concise and expressive syntax.
Take advantage of the wide range of plugins and extensions available in the Gradle ecosystem to enhance your build process.
Familiarize yourself with the Gradle documentation and community resources to learn more about advanced features and best practices.

Topic 6: Unit Testing

Unit Testing

What is it?
Unit testing is a software testing technique where individual components, such as classes or methods, are tested to ensure their correctness and functionality in isolation.

Where is it used?
Unit testing is used in software development to validate the behavior of small, independent units of code. It is commonly used in agile development practices, continuous integration, and test-driven development (TDD).

How is it used?
Identify the units to be tested: Identify the specific classes or methods that need to be tested in isolation.
Write test cases: Create test cases that cover different scenarios and expected outcomes for the unit being tested.
Set up the test environment: Set up any necessary dependencies or test data required for executing the unit tests.
Execute the tests: Run the unit tests to verify the behavior and functionality of the targeted units.
Validate the results: Check the test results to determine if the actual outputs match the expected outputs.
Analyze and fix issues: If any test cases fail, investigate the issues, identify the root causes, and fix the defects in the code.
Repeat the process: Continuously iterate the unit testing process as code changes or new features are added.

Example:

import org.junit.Test;
import static org.junit.Assert.assertEquals;

public class CalculatorTest {

    @Test
    public void testAddition() {
        Calculator calculator = new Calculator();
        int result = calculator.add(2, 3);
        assertEquals(5, result);
    }

    @Test
    public void testSubtraction() {
        Calculator calculator = new Calculator();
        int result = calculator.subtract(5, 3);
        assertEquals(2, result);
    }
    
    @Test
    public void testDivision() {
        Calculator calculator = new Calculator();
        double result = calculator.divide(10, 2);
        assertEquals(5.0, result, 0.001);
    }
}

Takeaways / Best Practices:

Unit tests should be focused and cover different scenarios to ensure adequate test coverage.
Use testing frameworks like JUnit or TestNG to write and execute unit tests effectively.
Test both the expected behavior and the handling of edge cases and boundary conditions.
Tests should be independent of each other and not rely on the order of execution.
Regularly run unit tests as part of the development process to catch issues early and ensure code quality.
Maintain a good balance between the number of unit tests and the time taken to execute them.
Refactor and update unit tests as the code evolves to keep them accurate and relevant.
Collaborate with other team members to establish consistent unit testing practices and share knowledge.

Topic 7: JUnit

JUnit

What is it?
JUnit is a popular unit testing framework for Java that provides a simple and standardized way to write and execute unit tests.

Where is it used?
JUnit is used in Java software development to automate the testing of individual units of code, such as classes or methods. It is widely adopted in industry and is integrated with various development tools and frameworks.

How is it used?

Set up the testing environment: Include the JUnit library in the project and set up the necessary testing dependencies.

Write test methods: Create test methods using the @Test annotation to specify the code to be tested.

Define assertions: Use assertion methods from the Assert class to validate the expected results of the tested code.

Set up preconditions: Use @Before annotated methods to define preconditions required for the test methods.

Perform cleanup: Use @After annotated methods to perform cleanup activities after the execution of each test method.

Run the tests: Use the test runner provided by JUnit to execute the test methods.

Analyze the results: Examine the test results to identify any failures or errors and investigate the causes.

Repeat and iterate: Modify the test cases or code under test as needed and rerun the tests until the desired functionality is achieved.

Example:

import org.junit.Test;
import static org.junit.Assert.*;

public class CalculatorTest {
    @Test
    public void testAddition() {
        Calculator calculator = new Calculator();
        int result = calculator.add(2, 3);
        assertEquals(5, result);
    }

    @Test
    public void testSubtraction() {
        Calculator calculator = new Calculator();
        int result = calculator.subtract(5, 3);
        assertEquals(2, result);
    }
    
    @Test
    public void testDivision() {
        Calculator calculator = new Calculator();
        double result = calculator.divide(10, 2);
        assertEquals(5.0, result, 0.001);
    }
}

Takeaways / Best Practices:

Write small, focused test methods that cover specific functionality.
Use meaningful test method names that describe the behavior being tested.
Use the various assertion methods provided by JUnit to validate expected results.
Leverage annotations like @Before and @After to set up preconditions and perform cleanup.
Group related test methods into test classes for better organization.
Regularly run the tests during development to catch issues early.
Aim for high test coverage to ensure thorough testing of the code.
Refactor and update tests as the code evolves to keep them in sync.
Use JUnit features like test suites, parameterized tests, and test fixtures as needed.
Collaborate with the development team to establish consistent testing practices and share knowledge.

Annotations

What is it?
Annotations are a form of metadata in Java that provide additional information about code elements, such as classes, methods, or fields.

Where is it used?
Annotations are used in various contexts, including:
Marking classes, methods, or fields with special characteristics or behaviors.
Providing instructions to the compiler or other tools.
Enabling frameworks or libraries to perform certain actions or configurations.

How is it used?
Declaration: Annotations are declared using the @ symbol followed by the annotation name.

Annotation targets: Annotations can be applied to classes, methods, fields, parameters, and other program elements based on their target specified in the annotation declaration.

Built-in annotations: Java provides several built-in annotations, such as @Override, @Deprecated, and @SuppressWarnings, which serve specific purposes.

Custom annotations: Developers can define their own custom annotations to add domain-specific metadata or behavior to their code.

Annotation processing: Annotations can be processed at compile-time or runtime using various techniques, such as reflection or annotation processing tools.

Framework integration: Annotations are commonly used in frameworks like Spring, Hibernate, and JUnit, where they play a crucial role in configuring and enhancing application behavior.

Example:

// Built-in annotation
@Override
public void run() {
// Code implementation
}

// Custom annotation
@CustomAnnotation(name = "MyAnnotation", value = "Hello")

public class MyClass {
// Class implementation
}

// Annotation processing
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.METHOD)

public @interface Loggable {
String value() default "";
}

public class Logger {
@Loggable("info")
public void logInfo(String message) {
// Logging implementation
}
}

// Framework integration (JUnit)
@Test
public void testAddition() {
// Test implementation
}

Takeaways / Best Practices:

Understand the purpose and usage of built-in annotations in Java.
Define custom annotations only when necessary and ensure they follow naming conventions.
Use annotations to communicate intent, provide additional information, or configure behavior.
Familiarize yourself with annotation processing techniques and tools available in Java.
Properly handle annotations at compile-time or runtime based on their requirements.
Be consistent with annotation usage across the codebase to maintain clarity.
Avoid excessive or unnecessary annotations that may clutter the code.
Stay updated with the annotations provided by frameworks and libraries you use.
Document the usage and meaning of custom annotations for better code understanding.
Regularly review and refactor annotations to keep them relevant and up to date.

Assertions

What is it?
Assertions are statements in Java that check for certain conditions and throw an exception if the condition is false, indicating a logical error in the code.

Where is it used?
Assertions are primarily used during development and testing to validate assumptions and detect programming errors.

How is it used?

Assertion syntax: Assertions are written using the assert keyword followed by a boolean expression that should evaluate to true.

Enabling assertions: Assertions are disabled by default in Java. To enable them, the -ea or -enableassertions flag is used when running the Java program.

Checking conditions: Assertions are used to verify conditions that should always be true at a specific point in the code.

Failure handling: If an assertion fails (i.e., the condition is false), an AssertionError is thrown, indicating a failure in the program logic.

Error messages: Assertions can include an optional error message to provide additional information about the failed condition.

Control flow impact: When assertions are enabled, a failed assertion will halt the program's execution.

Debugging and testing: Assertions are particularly useful during debugging and testing phases to catch logical errors and validate assumptions.

Example:

int age = 20;
assert age >= 18; // Assertion to check if age is greater than or equal to 18

String name = null;
assert name != null : "Name cannot be null"; // Assertion with an error message

// Enabling assertions
// java -ea MyProgram


// Assertion failure example
int x = 5;
assert x == 10 : "Invalid value of x"; // Assertion will fail and throw AssertionError

Takeaways / Best Practices:

Use assertions to validate assumptions and detect logical errors during development and testing.
Enable assertions during testing and debugging to catch failures early.
Focus on checking conditions that should always be true, rather than handling exceptional cases.
Avoid using assertions for input validation or handling user errors.
Provide meaningful error messages in assertions to aid in debugging.
Be aware that assertions are disabled by default and need to be explicitly enabled.
Do not rely on assertions for critical business logic or security checks.
Understand that assertions impact the program's control flow and can halt execution on failure.
Regularly review and validate assertions to ensure they remain relevant and accurate.
Consider using other testing frameworks (such as JUnit) for more extensive test coverage and flexibility.

Topic 8: Exception Handling

Exceptions

What is it?
Exceptions in Java are events that occur during the execution of a program, disrupting the normal flow and requiring special handling to prevent program termination.

Where is it used?
Exceptions are used in Java to handle various exceptional conditions that may arise during program execution, such as input/output errors, arithmetic errors, and null references.
How is it used?

Exception handling: Exceptions are handled using try-catch blocks, where the code that may throw an exception is enclosed within the try block, and the corresponding exception handling code is placed within catch blocks.

Catching exceptions: Catch blocks are used to catch and handle specific types of exceptions. Multiple catch blocks can be chained to handle different types of exceptions.

Handling exceptions: Exception handling code within catch blocks is executed when a specific exception occurs, allowing for appropriate actions such as error logging, user notifications, or fallback strategies.

Throwing exceptions: Exceptions can be explicitly thrown using the throw keyword to indicate an exceptional condition that cannot be handled locally. The thrown exception can be caught and handled in higher-level code.

Exception propagation: When an exception is thrown within a method and not caught locally, it propagates up the call stack until it is caught by an appropriate catch block or causes program termination.

Checked vs unchecked exceptions: Java differentiates between checked exceptions (required to be declared in method signatures or handled explicitly) and unchecked exceptions (not required to be declared or caught explicitly).

Exception hierarchy: Exceptions in Java follow a hierarchical structure, with Throwable as the root class, divided into checked exceptions (Exception) and unchecked exceptions (RuntimeException).

Finally block: The finally block is used to specify code that should be executed regardless of whether an exception occurs or not. It is commonly used for resource cleanup.

Example:

try {
    int result = divide(10, 0); // Code that may throw an exception
    System.out.println("Result: " + result);
} catch (ArithmeticException e) {
    System.out.println("Error: Division by zero");
} finally {
    System.out.println("Cleanup code here");
}

// Custom exception
public class CustomException extends Exception {
    public CustomException(String message) {
        super(message);
    }
}

public void validateAge(int age) throws CustomException {
    if (age < 0) {
        throw new CustomException("Invalid age");
    }
}

try {
    validateAge(-10); // Throwing a custom exception
} catch (CustomException e) {
    System.out.println("Error: " + e.getMessage());
}

Takeaways / Best Practices:

Use exceptions to handle exceptional conditions that can occur during program execution.
Choose appropriate exception types to accurately represent the exceptional situation.
Catch exceptions at the appropriate level to handle them effectively.
Provide meaningful error messages in exception handling code for better debugging and user experience.
Properly clean up resources in the finally block to ensure resource deallocation.
Be mindful of checked and unchecked exceptions and handle them accordingly.
Use custom exceptions when necessary to represent application-specific exceptional situations.
Avoid swallowing exceptions (i.e., catching exceptions without proper handling) as it can lead to silent failures.
Use exception propagation to allow higher-level code to handle exceptions when local handling is not appropriate.Keep exception handling code concise and focused on error recovery or graceful degradation.
Regularly review and validate exception handling code to ensure it is up to date and handles all relevant scenarios.

Type of Exceptions

What is it?
Types of exceptions in Java categorize exceptions based on their behavior and whether they are checked or unchecked.

Where is it used?
Types of exceptions are used in Java to classify exceptions into different categories based on their characteristics and how they should be handled.

How is it used?

Checked exceptions: These are exceptions that are checked at compile-time, meaning they must be declared in the method signature or handled explicitly using try-catch blocks. Examples include IOException, SQLException, and ClassNotFoundException.

Unchecked exceptions: These are exceptions that are not checked at compile-time and do not require explicit handling. They extend the RuntimeException class or its subclasses. Examples include NullPointerException, ArrayIndexOutOfBoundsException, and ArithmeticException.

Error: Errors are exceptional conditions that usually cannot be handled by the application. They are serious problems that typically indicate a severe system failure or resource exhaustion. Examples include OutOfMemoryError and StackOverflowError.

Custom exceptions: Java allows creating custom exceptions by extending the Exception class or its subclasses. Custom exceptions can be used to represent application-specific exceptional situations.

Example:

// Checked exception
public void readFile(String fileName) throws IOException {
    FileReader fileReader = new FileReader(fileName);
    // Code to read the file
    fileReader.close();
}

// Unchecked exception
public int divide(int a, int b) {
    if (b == 0) {
        throw new ArithmeticException("Divisor cannot be zero");
    }
    return a / b;
}

// Error
public void runOutOfMemory() {
    int[] array = new int[Integer.MAX_VALUE];
}

// Custom exception
public class CustomException extends Exception {
    public CustomException(String message) {
        super(message);
    }
}

public void validateAge(int age) throws CustomException {
    if (age < 0) {
        throw new CustomException("Invalid age");
    }
}

Takeaways / Best Practices:

Understand the distinction between checked exceptions, unchecked exceptions, errors, and custom exceptions.
Use checked exceptions for conditions that can be anticipated and handled by the calling code.
Handle checked exceptions either by declaring them in the method signature or using try-catch blocks.
Unchecked exceptions are usually caused by programming errors and are not required to be explicitly handled.
Errors indicate severe system problems and are typically not recoverable. They should be logged and reported.
Create custom exceptions to represent application-specific exceptional situations and provide meaningful error messages.
Choose appropriate exception types to accurately represent the exceptional condition and aid in debugging.
Document the exceptions thrown by methods using Javadoc or other documentation tools.
Avoid catching and ignoring exceptions without appropriate handling, as it can lead to unexpected behavior and silent failures.
Regularly review exception handling code to ensure it is up to date and handles all relevant scenarios.
Use appropriate exception handling strategies to ensure proper error recovery, graceful degradation, and resource cleanup.

try-catch-finally block

What is it?
The try-catch-finally block is a construct in Java used to handle exceptions. It allows for catching and handling exceptions that may occur within a block of code, and ensures that certain cleanup operations are performed regardless of whether an exception occurs or not.

Where is it used?
The try-catch-finally block is used in Java when there is a need to handle exceptions that can potentially occur during the execution of a block of code.

How is it used?
The code that may throw an exception is enclosed within the try block.

The catch block(s) immediately follow the try block and specify the type(s) of exceptions to be caught and handled.

If an exception of the specified type occurs within the try block, the corresponding catch block is executed.

After the catch block(s), the finally block is executed regardless of whether an exception occurred or not.

The finally block is used to perform cleanup operations, such as closing resources, that should always be executed.

The finally block is optional, but if present, it ensures that the specified cleanup operations are performed, even if an exception is thrown and not caught.

Example:

try {
    // Code that may throw an exception
    int result = divide(10, 0);
    System.out.println("Result: " + result);
} catch (ArithmeticException e) {
    // Exception handling code for ArithmeticException
    System.out.println("Cannot divide by zero");
} finally {
    // Cleanup code that always gets executed
    System.out.println("Performing cleanup");
}

Takeaways / Best Practices:

Use the try-catch-finally block to handle exceptions and ensure necessary cleanup operations.
Place the code that may throw an exception within the try block.
Catch specific types of exceptions in separate catch blocks to handle them appropriately.
Handle exceptions gracefully by providing meaningful error messages and appropriate error recovery strategies.
Use the finally block to perform cleanup operations that must be executed, such as releasing resources (closing files, database connections, etc.).
The finally block is useful for ensuring cleanup even if an exception occurs or if a return statement is encountered within the try or catch blocks.
If a return statement is encountered within the try or catch blocks, the finally block is executed before returning from the method.
Avoid catching exceptions without appropriate handling or simply logging the exception without taking any corrective action.
Be cautious when modifying variables within the finally block, as it may affect the behavior of the code.
Consider using try-with-resources (available from Java 7 onwards) for automatic resource management, which eliminates the need for explicit finally blocks for resource cleanup.
Properly document the exceptions that can be thrown by a method using Javadoc or other documentation tools.

Exception Class Hierarchy

What is it?
The Exception class hierarchy in Java represents a hierarchical structure of exception classes that are used to handle and propagate exceptions in a program.

Where is it used?
The Exception class hierarchy is used in Java to categorize and handle different types of exceptions that may occur during the execution of a program. It provides a structured way to organize and handle exceptions based on their type and behavior.

How is it used?
The Exception class hierarchy in Java consists of a root class called java.lang.Throwable, which is the superclass for all exceptions and errors. The hierarchy is divided into two main branches:

Checked Exceptions:
These are exceptions that must be declared in the method signature or handled explicitly using try-catch blocks.

They are subclasses of the java.lang.Exception class, excluding subclasses of RuntimeException.

Examples include IOException, SQLException, etc.

Unchecked Exceptions:
These are exceptions that do not need to be declared in the method signature or explicitly handled.

They are subclasses of RuntimeException or its subclasses.

Examples include NullPointerException, ArrayIndexOutOfBoundsException, etc.

Example:

try {
    // Code that may throw exceptions
    // ...
} catch (IOException e) {
    // Handling IOException
    // ...
} catch (NullPointerException e) {
    // Handling NullPointerException
    // ...
} catch (Exception e) {
    // Catching any other checked exceptions
    // ...
} catch (RuntimeException e) {
    // Catching any unchecked exceptions
    // ...
} finally {
    // Cleanup code or other necessary operations
    // ...
}

Takeaways / Best Practices:

Understand the hierarchy of exception classes to effectively handle different types of exceptions.
Catch exceptions at an appropriate level of granularity to provide targeted handling and error recovery.
Follow best practices for exception handling, such as providing meaningful error messages, logging exceptions, and taking appropriate corrective actions.
Be aware of checked and unchecked exceptions and handle them accordingly.
Use multiple catch blocks to handle different types of exceptions separately.
Place more specific catch blocks before more general catch blocks to ensure proper handling.
Use the finally block for cleanup operations and resource management.
Avoid catching exceptions without appropriate handling or simply logging exceptions without taking any corrective action.
Document the exceptions that can be thrown by a method using Javadoc or other documentation tools to guide users of the method.

Topic 9: Object Class Methods

getClass Method

What is it?
The getClass() method in Java is a method defined in the Object class that returns the runtime class of an object.

Where is it used?
The getClass() method is used when you need to determine the class of an object at runtime. It is commonly used in situations where you want to perform operations based on the specific class of an object.

How is it used?
Use the getClass() method to retrieve the runtime class of an object:
Obtain a reference to the object whose class you want to determine.
Call the getClass() method on the object.
Store the result in a Class object or use it directly for further processing.

Example:

// Creating an object of type String
String str = "Hello, World!";

// Getting the class of the object
Class<? extends String> clazz = str.getClass();

// Printing the class name
System.out.println(clazz.getName());  // Output: java.lang.String

Takeaways / Best Practices:

The getClass() method is available for all objects in Java since it is defined in the Object class, which is the root of the class hierarchy.
The returned Class object provides information about the object's runtime class, including its name, methods, fields, and interfaces.
Use getClass() when you need to perform runtime type checks or dynamically determine the class of an object.
Avoid using getClass() for general comparisons of object types. Instead, consider using the instanceof operator or Class methods like isAssignableFrom() for type checking.
Be aware that the getClass() method returns the runtime class of an object, which may differ from the compile-time type if the object is an instance of a subclass.
The Class object obtained from getClass() can be used for reflection, dynamic instantiation, method invocation, and other reflective operations.

toString Method

What is it?
The toString() method in Java is a method defined in the Object class that returns a string representation of an object.

Where is it used?
The toString() method is used when you want to obtain a meaningful string representation of an object. It is commonly used for debugging, logging, and displaying object information.

How is it used?
Use the toString() method to get a string representation of an object:
Implement the toString() method in your custom class.
Inside the toString() method, construct a string representation that includes relevant information about the object's state.
Return the constructed string representation.

Example:

// Custom class representing a person
class Person {
    private String name;
    private int age;

    // Constructor and other methods...

    // Implementing the toString() method
    @Override
    public String toString() {
        return "Person{name='" + name + "', age=" + age + "}";
    }
}

// Creating an object of type Person
Person person = new Person("John Doe", 30);

// Calling the toString() method implicitly or explicitly
System.out.println(person);  // Output: Person{name='John Doe', age=30}

Takeaways / Best Practices:

Implementing the toString() method provides a concise and meaningful representation of an object's state.
Override the toString() method in your custom classes to provide a customized string representation.
Include relevant information about the object's state in the toString() method's implementation.
Avoid including sensitive or unnecessary information in the toString() output.
The toString() method is automatically called when an object is used in a string concatenation or when it is passed to methods like println().
Consider using libraries like Apache Commons Lang or Guava for generating toString() implementations automatically.
Ensure that the toString() method returns a non-null string to avoid NullPointerExceptions in scenarios where the object may be null.

hashCode Method

What is it?
The hashCode() method in Java is a method defined in the Object class that returns a unique integer value representing the object's state.

Where is it used?
The hashCode() method is used when you want to generate a hash code for an object. It is commonly used in hash-based data structures like HashMap, HashSet, etc., to determine the object's storage location or to check for equality.

How is it used?
Use the hashCode() method to generate a hash code for an object:
Implement the hashCode() method in your custom class.
Inside the hashCode() method, compute a unique integer value based on the object's state.
Return the computed hash code.

Example:

// Custom class representing a person
class Person {
    private String name;
    private int age;

    // Constructor and other methods...

    // Implementing the hashCode() method
    @Override
    public int hashCode() {
        int result = name != null ? name.hashCode() : 0;
        result = 31 * result + age;
        return result;
    }
}


// Creating an object of type Person
Person person = new Person("John Doe", 30);

// Getting the hash code using the hashCode() method
int hashCode = person.hashCode();
System.out.println("Hash Code: " + hashCode);

Takeaways / Best Practices:

The hashCode() method should return the same hash code for objects that are equal according to the equals() method.
Override the hashCode() method in your custom classes when you override the equals() method.
Include the same set of fields used in the equals() method while computing the hash code to ensure consistency.
Use a combination of prime numbers and the 31 constant to calculate the hash code for multiple fields to reduce collisions.
The hashCode() method is used in hash-based data structures to distribute objects efficiently.
The hash code of an object should ideally be based on immutable fields to ensure consistency.
It is not necessary for two different objects to have different hash codes, but objects that are considered equal should have the same hash code.

equals Method

What is it?
The equals() method in Java is a method defined in the Object class that checks for the equality of two objects based on their state.

Where is it used?
The equals() method is used when you want to compare the equality of objects. It is commonly used in collections like ArrayList, HashSet, etc., to determine if an object is already present or to perform custom equality checks.

How is it used?

Use the equals() method to compare the equality of objects:
Implement the equals() method in your custom class.
Inside the equals() method, compare the state of the current object with the state of the object being passed as an argument.

Return true if the objects are equal, false otherwise.

Example:

// Custom class representing a point in 2D space
class Point {
    private int x;
    private int y;
    // Constructor and other methods...

    // Implementing the equals() method
    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }


        if (obj == null || getClass() != obj.getClass()) {
            return false;
        }


        Point other = (Point) obj;
        return x == other.x && y == other.y;

    }

}

// Creating two objects of type Point
Point point1 = new Point(2, 3);
Point point2 = new Point(2, 3);

// Checking equality using the equals() method
boolean isEqual = point1.equals(point2);
System.out.println("Are points equal? " + isEqual);

Takeaways / Best Practices:

Override the equals() method in your custom classes to define custom equality checks.
Ensure that the equals() method follows the rules of an equivalence relation: reflexive, symmetric, and transitive.
Always perform a type check using getClass() before comparing the state of objects.
Use the instanceof operator to handle cases where objects of different classes can be considered equal.
Consider overriding the hashCode() method when overriding the equals() method to maintain the contract between the two methods.
Use the equals() method to compare the state of objects, not their references.
Avoid throwing exceptions in the equals() method and handle null and self-reference cases appropriately.

Thank you and Keep Learning!