throws

1. What is throws?

throws is used in a method's signature to declare that the method might produce a certain type of exception, so whoever calls that method knows they must handle it.

2. Why is it used?

It acts as a warning label on a method, telling other developers (and the compiler) that calling this method carries a risk that must be dealt with, usually with a try-catch.

3. Real-Life Example

Think of a warning label on a product box saying "May cause allergic reaction — check ingredients." It doesn't cause the reaction itself, but it warns the user in advance that there's a certain risk involved.

4. Syntax

java
returnType methodName() throws ExceptionType {
    // method body
}

5. Example Program

java
import java.io.IOException;

public class ThrowsDemo {
    static void readFile() throws IOException {
        throw new IOException("File not found");
    }

    public static void main(String[] args) {
        try {
            readFile();
        } catch (IOException e) {
            System.out.println("Handled: " + e.getMessage());
        }
    }
}

Output:

Handled: File not found

6. Key Points to Remember

• throws is written in the method signature; throw is used inside the method body to actually trigger an exception.
• A method can declare multiple exception types using throws, separated by commas.
• throws is mainly required for checked exceptions (explained further in topic 71).