Handling “Null Pointer Exception” in a Class using OOPS in Java

Error Manifestation: Null Pointer Exception in a Class using OOPS in Java

Understand the Error: Null pointer exception is one of the most common errors encountered while working with object-oriented programming concepts in Java. It occurs when a reference variable with a null value is used to access a member of an object. In other words, when an object is not initialized and we try to access its members, it results in null pointer exception.

Cause:

• When an object is not initialized and we try to access its members

Check: Can you check where this error is occurring in your code? (Exact file name and line no.)

Check: Check if any of the above cause is applicable for your code? Why do you think the error is being thrown on this line?

Example code snippet:

public class MyClass {

String name;

public void displayName() {`

System.out.println(name.length());

}

public static void main(String[] args) {

MyClass obj = new MyClass();

obj.displayName();

}

}

In the above example, we have a class named MyClass with a member variable name. We are trying to access the length of the name variable in the displayName() method, but we have not initialized it yet. When we run this code, it will result in null pointer exception as name is not initialized.

Debugging the Error:

1. Check the line number where the null pointer exception is occurring and identify the reference variable causing the exception.

2. Make sure that the object is initialized before accessing its members.

3. Use null checks to avoid null pointer exceptions. For example, we can add an if-else statement to check if the object is null before accessing its members.

public void displayName() {

if(name != null) {

System.out.println(name.length());

}

}

d. Use try-catch blocks to handle null pointer exceptions gracefully and provide an appropriate error message.

Extra Information:

1. Always initialize objects before accessing their members to avoid null pointer exceptions.

2. Null pointer exceptions can also occur when we pass null as an argument to a method expecting a non-null object.

3. Using optional or nullable types can also help avoid null pointer exceptions in Java.