Java Programs›Exceptions›Unchecked Exception

Unchecked Exception in Java

beginner· Exceptions · Error Handling

Problem

An unchecked exception extends RuntimeException, and the compiler never requires it to be caught or declared — code compiles fine whether or not it's handled.

Reject an invalid argument by throwing an unchecked exception, and catch it at the call site.

Input

age = -5

Output

Error: Age cannot be negative

Java Program

Java

public class UncheckedExceptionDemo {
    static void setAge(int age) {
        if (age < 0) {
            throw new IllegalArgumentException("Age cannot be negative"); // unchecked — no throws clause needed here
        }
        System.out.println("Age set to " + age);
    }

    public static void main(String[] args) {
        try {
            setAge(-5);
        } catch (IllegalArgumentException e) {
            System.out.println("Error: " + e.getMessage());
        }
    }
}

▶ Run Code

Output

Error: Age cannot be negative

Core Logic

Throwing IllegalArgumentException when a precondition fails signals a programming/usage error without forcing every caller to prove they've handled it.

How It Works

1setAge(int age) checks age < 0 and throws IllegalArgumentException if the check fails.
2IllegalArgumentException extends RuntimeException, making it unchecked — setAge needs no throws clause, and this code would compile even with no try/catch around the call at all.
3The caller here chooses to wrap the call in try/catch anyway, but that's a choice, not a compiler requirement.
4catch (IllegalArgumentException e) receives the exception and reads its message back.

Calling setAge(-5) throws immediately, caught and printed as "Error: Age cannot be negative".

💡

Key Point: Removing the try/catch entirely and letting the exception propagate uncaught would still compile — that's the defining difference from a checked exception, which the compiler refuses to allow unhandled.

Key Concepts

unchecked exceptionIllegalArgumentExceptionRuntimeException

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