Java - Throws and Throw: How to Handle Exceptions

Understand the difference between throws and throw in Java. Learn how to use throws to declare exceptions in methods and throw to explicitly throw an exception, enabling better exception handling in your Java applications.

Java - Throws and Throw | Throw an Exception

Java Throws and Throw

In Java, if a method does not handle a checked exception, it must declare it using the throws keyword. This keyword is placed at the end of the method's signature. You can throw an exception, either by creating a new instance or by using an exception that you have caught, with the throw keyword.

It's important to understand the difference between throws and throw: throws is used to postpone handling a checked exception, while throw is used to explicitly invoke an exception.

Syntax

The syntax for throwing an exception using throws and throw is as follows:

method(parameters) throws exception {
// Method implementation
throw new exception();
}
    

The following method declares that it throws a RemoteException:

import java.io.*;

public class ClassName {
public void deposit(double amount) throws RemoteException {
    // Method implementation
    throw new RemoteException();
}
// Remainder of class definition
}
    

A method can declare that it throws multiple exceptions by listing them, separated by commas. For instance:

import java.io.*;

public class ClassName {
public void withdraw(double amount) throws RemoteException, InsufficientFundsException {
    // Method implementation
}
// Remainder of class definition
}
    

Learn Java in-depth with real-world projects through our Java certification course. Enroll and become a certified expert to boost your career.

Java Throws and Throw Example

The following example demonstrates the use of the throw keyword to send an exception when an invalid argument is passed. We call a divide method that checks if the second parameter is zero. If it is, it throws an IllegalArgumentException with a custom message. Since IllegalArgumentException is an unchecked exception, the divide method is not required to declare a throws statement. When the parent method does not handle the exception, the JVM intercepts it, prints the error message, and terminates the program.

package com.tutorialsarena;

public class ExcepTest {
public static void main(String args[]) {
    int a = 3;
    int b = 0;
    System.out.println("result: " + divide(a, b));
}

private static int divide(int a, int b) {
    if (b == 0) {
        throw new IllegalArgumentException("Second argument cannot be zero.");
    }
    return a / b;
}
}
    

Exception in thread "main" java.lang.IllegalArgumentException: Second argument cannot be zero.
at com.tutorialsarena.ExcepTest.divide(ExcepTest.java:13)
at com.tutorialsarena.ExcepTest.main(ExcepTest.java:8)
    

More Examples

Example 1: Throwing an Exception for Invalid Arguments

This example shows the use of throw and throws keywords to send an exception when an invalid argument is passed and handle the exception. We call the divide method which checks if the second parameter is zero, and if so, it throws an exception with a custom message. Since the Exception is a checked exception, the divide method must declare a throws statement. In this case, the parent method handles the exception and prints the message.

package com.tutorialsarena;

public class ExcepTest {
public static void main(String args[]) {
    int a = 3;
    int b = 0;
    try {
        System.out.println("result: " + divide(a, b));
    } catch (Exception e) {
        System.out.println("Exception: " + e);
    }
}

private static int divide(int a, int b) throws Exception {
    if (b == 0) {
        throw new Exception("Second argument cannot be zero.");
    }
    return a / b;
}
}
    

Exception: java.lang.Exception: Second argument cannot be zero.
    

Example 2: Using Throws and Throw in Main and Other Methods

This example illustrates the use of throw and throws keywords to throw an exception when an invalid argument is passed and the exception is not handled. We call the divide method which checks if the second parameter is zero and throws an exception with a custom message. Since Exception is a checked exception, the divide method must declare a throws statement. In this case, the parent method declares the exception, allowing the JVM to handle it.

package com.tutorialsarena;

public class ExcepTest {
public static void main(String args[]) throws Exception {
    int a = 3;
    int b = 0;
    System.out.println("result: " + divide(a, b));
}

private static int divide(int a, int b) throws Exception {
    if (b == 0) {
        throw new Exception("Second argument cannot be zero.");
    }
    return a / b;
}
}
    

Exception in thread "main" java.lang.Exception: Second argument cannot be zero.
at com.tutorialsarena.ExcepTest.divide(ExcepTest.java:15)
at com.tutorialsarena.ExcepTest.main(ExcepTest.java:9)