Exception handling is an important feature in Java that helps developers manage runtime errors gracefully.

Two commonly used keywords in exception handling are:

1. throw
2. throws

Although they look similar, they serve different purposes.

What is throw in Java?

The throw keyword is used to explicitly create and throw an exception from a method or block of code.

Syntax

throw new ExceptionType("Error Message");

Example

public class ThrowExample {

public static void main(String[] args) {

    int marks = -10;

    if (marks < 0) {
        throw new ArithmeticException("Marks cannot be negative");
    }

    System.out.println("Valid Marks");
}

}

Output

Exception in thread "main"
java.lang.ArithmeticException: Marks cannot be negative

Key Points of throw

• Used to explicitly throw an exception.

• Followed by an exception object.

• Throws only one exception at a time.

• Can throw both checked and unchecked exceptions.

• Used inside method body.

What is throws in Java?

The throws keyword is used in a method declaration to indicate that the method may throw one or more exceptions.

It informs the caller of the method that exception handling is required.

Syntax

returnType methodName() throws ExceptionType {
// code
}

Example

import java.io.IOException;

public class ThrowsExample {

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(e.getMessage());
    }
}

}

Output

File not found

Key Points of throws

• Used in method declaration.

• Declares possible exceptions.

• Can declare multiple exceptions.

• Mainly used for checked exceptions.

• Responsibility is passed to the caller.

Example Using Both throw and throws

import java.io.IOException;

public class Demo {

static void validateAge(int age) throws IOException {

    if(age < 18) {
        throw new IOException("Not eligible to vote");
    }

    System.out.println("Eligible to vote");
}

public static void main(String[] args) {

    try {
        validateAge(15);
    }
    catch(IOException e) {
        System.out.println(e.getMessage());
    }
}

}

Output

Not eligible to vote

Explanation

• throws IOException declares that the method may throw an IOException.
• throw new IOException() actually creates and throws the exception.
• The caller handles it using try-catch.

Difference Between throw and throws