Number Format Exception Example in Java

Introduction

Number Format 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{
    //Do something
}catch(java.lang.NumberFormatException e){
    //Do something with the caught exception
}

NumberFormat Exception Example Program

public class NumberFormatException {
    static void numberConversion(String input){
        try{
            int number = Integer.parseInt(input);
            System.out.println("The input integer after conversion is : "+number);
        }catch(java.lang.NumberFormatException e){
            System.out.println("Error!!! While converting input to integer");
        }
    }
    
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.println("Enter the string to be converted to an integer : ");
        String input = scanner.nextLine();
        numberConversion(input);
    }
}

Sample Output

Enter the string to be converted to an integer : 
12
The input integer after conversion is : 12

When to use

Use this number format 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. int number = Integer.parseInt(input); updates a variable used in the calculation or output.

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

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

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

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

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

8. Compare your console output with the sample output for Number Format 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.