Null Pointer Exception Example in Java

Introduction

Null Pointer Exception is a classic Java console program that demonstrates the concept with complete source code and sample output. Exceptions represent runtime errors; Java uses try-catch-finally to handle them safely.

This tutorial walks through the program line by line, explains how the logic works, and highlights best practices you can apply in your own code.

Syntax

try{
	//Statements
}catch(Expression_type Variable_name){
	//Statements
}

Null Pointer Exception Example Program

public class NullPointerException {
    static void getLength(String text){
        try{
        System.out.println("Length of the input string is  : "+text.length());
        }catch(Exception e){
            System.out.println("Exception while trying to find length of input : "+e.toString());
        }
    }
    
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("Enter the text to find length : ");
        String text = scanner.nextLine();
        if(text.length()==0){
            //Pass null as input if input is empty
            text = null;
        }
        getLength(text);
    }
}

Sample Output

Enter the text to find length : 

Exception while trying to find length of input : java.lang.NullPointerException

When to use

Use this null pointer exception example when learning or revising core Java syntax.

How it works

1. Execution begins in the main method — the JVM calls this method when you run the class.

2. A println / print call writes text to the console — part of the sample output below.

3. A println / print call writes text to the console — part of the sample output below.

4. A Scanner reads typed input from the keyboard (System.in).

5. A println / print call writes text to the console — part of the sample output below.

6. String text = scanner.nextLine(); updates a variable used in the calculation or output.

7. The if statement runs the nested code only when the condition is true.

8. Compare your console output with the sample output for Null Pointer Exception to confirm the program behaves correctly.

Best Practices

• Use meaningful variable and class names that describe their purpose.
• Compile and run the program locally — modify values to see how output changes.
• Read compiler errors carefully; they usually point to the exact line to fix.

Common Mistakes

• Copying code without understanding each line — practice by changing one statement at a time.
• Mismatching the public class name and the .java filename.
• Forgetting semicolons at the end of statements.