Throw keyword in Java - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Java code using throw?

Consider the following Java code snippet. What will be printed when it runs?

Java

public class TestThrow {
    public static void checkAge(int age) {
        if (age < 18) {
            throw new IllegalArgumentException("Age must be at least 18");
        } else {
            System.out.println("Access granted");
        }
    }
    public static void main(String[] args) {
        try {
            checkAge(16);
        } catch (IllegalArgumentException e) {
            System.out.println(e.getMessage());
        }
    }
}

A Age must be at least 18

B Exception in thread "main" java.lang.IllegalArgumentException: Age must be at least 18

C Access granted

D Compilation error

💡 Hint

Look at what happens when age is less than 18 and how the exception is handled.

The method throws an IllegalArgumentException when age is less than 18. The main method catches this exception and prints its message, which is "Age must be at least 18".

❓ Predict Output

intermediate

What happens when throw is used without catch?

What will be the output or result of this Java program?

Java

public class ThrowWithoutCatch {
    public static void main(String[] args) {
        throw new RuntimeException("Error occurred");
    }
}

A Program compiles but throws RuntimeException and terminates with stack trace

B Program runs silently with no output

C Compilation error: unhandled exception

D Program prints: Error occurred

💡 Hint

RuntimeException is unchecked. What happens if it is thrown but not caught?

Throwing a RuntimeException without catching it causes the program to terminate and print the exception's stack trace and message.

🔧 Debug

advanced

Identify the error in this throw usage

This Java code tries to throw an exception. What is the error?

Java

public class ThrowError {
    public static void main(String[] args) {
        throw new Exception("Checked exception");
    }
}

A Syntax error: throw keyword used incorrectly

B Compilation error: unhandled checked exception

C Runtime error: Exception thrown but not caught

D No error, code runs fine

💡 Hint

Exception is a checked exception. What does Java require for checked exceptions?

Checked exceptions must be either caught or declared to be thrown. This code neither catches nor declares the exception, causing a compilation error.

🧠 Conceptual

advanced

What is the effect of throw inside a method?

When a method uses the throw keyword to throw an exception, what happens immediately after the throw statement executes?

A The method pauses and waits for user input

B The method continues executing the next statement after throw

C The method terminates immediately and control transfers to the nearest catch block

D The method restarts from the beginning

💡 Hint

Think about what throw does to the normal flow of a program.

Throwing an exception immediately stops the current method execution and transfers control to the nearest matching catch block or terminates the program if none is found.

❓ Predict Output

expert

What is the output of nested throw and catch blocks?

Analyze the output of this Java program with nested try-catch and throw statements.

Java

public class NestedThrowCatch {
    public static void main(String[] args) {
        try {
            try {
                throw new IllegalArgumentException("Inner exception");
            } catch (NullPointerException e) {
                System.out.println("Caught NullPointerException");
            }
        } catch (IllegalArgumentException e) {
            System.out.println(e.getMessage());
        }
    }
}

A Caught NullPointerException

B Compilation error due to nested try-catch

C No output, program runs silently

D Inner exception

💡 Hint

Which catch block matches the thrown exception type?

The inner try throws IllegalArgumentException, which is not caught by the inner catch (which catches NullPointerException). The outer catch catches IllegalArgumentException and prints its message.