Re-throw Exception Example in Java

Introduction

Re-Throw 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(Exception e){
   //throwing caught exception
    throw e;
}

Re-Throw Exception Example Program

public class ReThrowException {
    static void getStringLength(){
        try{
            String text = null;
            int length = text.length();
        }catch(Exception e){
            System.out.println("Caught exception : "+e.toString());
            throw e;
        }
    }
    
    public static void main(String[] args) {
        try{
            getStringLength();
        }catch(Exception e){
            System.out.println("Caught re-thrown exception : "+e.toString());
        }
    }
}

Sample Output

Caught exception : java.lang.NullPointerException
Caught re-thrown exception : java.lang.NullPointerException

When to use

Use this re-throw 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. String text = null; updates a variable used in the calculation or output.

3. int length = text.length(); updates a variable used in the calculation or output.

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

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

6. Compare your console output with the sample output for Re-Throw 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.