Java throw and throws Keyword

Exception handling is one of the most important features of Java. It helps developers handle runtime errors gracefully and keep applications stable.
Among Java’s exception-handling tools, throw and throws are often confusing for beginners.

In this article, we’ll clearly understand what throw and throws are, how they differ, and when to use each, with simple examples.

What is an Exception in Java?

An exception is an unwanted or unexpected event that occurs during the execution of a program and disrupts its normal flow.

Examples:

Dividing a number by zero

Accessing an invalid array index

Opening a file that does not exist

Java provides a powerful mechanism to handle these issues using exception handling.

Java throw Keyword

What is throw?

The throw keyword is used to explicitly create and throw an exception in a program.

It is mainly used when a programmer wants to manually signal an error condition.

Syntax of throw

throw new ExceptionType("Error message");

Example of throw

public class ThrowExample {
    public static void main(String[] args) {
        int age = 15;
if (age < 18) {
            throw new ArithmeticException("Not eligible to vote");
        }
        System.out.println("You can vote");
    }
}

Output

Exception in thread "main" java.lang.ArithmeticException: Not eligible to vote

Here, we manually throw an exception when the condition is not satisfied.

Key Points about throw

Used inside a method or block

Throws one exception at a time

Used to create custom or predefined exceptions

Followed by an exception object

Java throws Keyword

What is throws?

The throws keyword is used in a method declaration to indicate that the method may pass an exception to the calling method.

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It does not handle the exception — it only declares it.

Syntax of throws

returnType methodName() throws ExceptionType {
    // code
}

Example of throws

import java.io.*;
public class ThrowsExample {
    static void readFile() throws IOException {
        FileReader file = new FileReader("test.txt");
        BufferedReader br = new BufferedReader(file);
        br.readLine();
    }
    public static void main(String[] args) throws IOException {
        readFile();
    }
}

Here, the exception responsibility is passed to the caller.

Key Points about throws

Used with method declaration

Can declare multiple exceptions

Mainly used for checked exceptions

Does not create an exception

throw vs throws – Simple Example Together

class Test {
static void checkNumber(int num) throws ArithmeticException {
        if (num < 0) {
            throw new ArithmeticException("Number cannot be negative");
        }
        System.out.println("Valid number");
    }
    public static void main(String[] args) {
        checkNumber(-5);
    }
}

✔ throws declares the exception
✔ throw actually throws it

When to Use throw and throws?

Use throw when you want to manually trigger an exception

Use throws when you want the caller to handle the exception

Use both together for clean and reusable code

Real-World Use Case

In real applications:

throw is used in business logic validation

throws is used in service layers and APIs

This separation improves readability, debugging, and maintenance.

Conclusion

Understanding the difference between throw and throws is essential for writing clean and professional Java code.

throw → Creates and throws an exception
throws → Declares and passes an exception

Mastering these keywords will help you build robust, error-free Java applications.

Free Resources:

Video Lecture: https://youtu.be/mtEC1DYsX5Q?si=n_uI8X7-mUU_leRu

Exercise Practice: https://www.quipoin.com/exercise/java/throw-and-throws-keyword

Interview Practice: https://www.quipoin.com/interview/java/throw-and-throws-keyword

MCQs Practice: https://www.quipoin.com/practice-mcqs/java/throw-and-throws-keyword