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Java Exception Handling MCQ Test

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Throwing Exceptions

 In Java, the `throw` statement is used to explicitly throw an exception within a method or block of code. It is typically used when an exceptional condition occurs that the method cannot handle itself, and it wants to signal to the calling code that something went wrong.

Syntax:

throw throwableObject;


Explanation:

- The `throw` statement requires an argument, which is usually an instance of a subclass of `Throwable` (either an exception or an error).

- The argument passed to `throw` can be any expression that results in a throwable object.

- When a `throw` statement is executed, the program flow is immediately transferred out of the current method or block and back to the calling code.

- The caller can then catch the thrown exception using a `try-catch` block or propagate it further up the call stack.


Example:

public class AgeValidator {

    public static void validateAge(int age) {

        if (age < 0) {

            throw new IllegalArgumentException("Age cannot be negative");

        }

        if (age < 18) {

            throw new RuntimeException("Must be at least 18 years old");

        }

        System.out.println("Age is valid");

    }


    public static void main(String[] args) {

        try {

            validateAge(20);

            validateAge(-5); // This will throw an IllegalArgumentException

        } catch (IllegalArgumentException e) {

            System.out.println("IllegalArgumentException: " + e.getMessage());

        } catch (RuntimeException e) {

            System.out.println("RuntimeException: " + e.getMessage());

        }

    }

}



In this example, the `validateAge` method throws either an `IllegalArgumentException` or a `RuntimeException` based on the age provided. The `main` method catches these exceptions and prints appropriate error messages.


Analogy:

Imagine you are a lifeguard at a swimming pool. When you see someone struggling in the water (an exceptional condition), you throw a lifeline or buoy (an exception) to help them. The lifeline indicates to others that there is a problem and needs attention. Similarly, when an exceptional condition occurs in a Java program, the `throw` statement signals to the calling code that something unexpected has happened and needs to be addressed.

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