Difference Between throw and throws in Java with Examples

 

What is throw and throw keywords in Java? What is Difference between throw and throws?

In java, throw and throws keyword are used for Exception Declaration. throw and throws keywords are mainly used for handle the Exception. 

What is Exception and Exception handling in Java?

•  Exception and Exception handling in Java
  

So let's see how both are different from each other.

1. throw

As a name suggest, throw is used to throw the Exception in java. Using throw keyword we can throw exception explicitly.

throw keyword used inside of method. It is used when it is required to throw an Exception logically. 

We can throw only one Exception at a time.

Syntax of throw :-

    throw someThrowableObject

Lets see example of throw keyword so you will get idea about it.

Example 1 :- throw exception using throw keyword

public class ExceptionDemo {

    public static void main(String[] args) {
        method();
    }
    
    public static void method() {
        System.out.println("Inside Method");
        throw new RuntimeException();
    }

}

Inside Method
Exception in thread "main" java.lang.RuntimeException
    at ExceptionDemo.method(ExceptionDemo.java:9)
    at ExceptionDemo.main(ExceptionDemo.java:4)

In above example we does not catch the exception so its throw exception trace status in output. we can also catch Exception after throw. 

Example 2 :- Handle the Exception after throw

public class ExceptionDemo {

    public static void main(String[] args) {
        try {
            method();
        } catch (Exception e) {
            System.out.println("Handled the Exception");
        }
    }
    
    public static void method() {
        System.out.println("Inside Method");
        throw new RuntimeException();
    }

}

Inside Method
Handled the Exception

2. throws 

throws keyword is used with method signature. throws keyword is used when the method has some statement that can lead to some Exception. 

we can declare multiple exception using throws keyword, separated by comma.

Syntax :-

    public void method() throws Exception {  
       // Some code
    }

Let's see example of throws keyword

Example 3 :- Declare Run time (Unchecked) exception using throws keyword

public class ExceptionDemo {

    public static void main(String[] args) {
        try {
            method();
        } catch (Exception e) {
            System.out.println("Handled the Runtime Exception");
        }
    }
    
    public static int method() throws ArithmeticException {
        int number1 = 10;
        int number2 = 0;
        return number1/number2;
    }

}

Output :-
Handled the Runtime Exception

If we throw Runtime Exception then it is not necessary to catch. It is depend on developer to handle or not.

Example 4 :- Declare Compile time (Checked) exception using throws keyword

import java.io.FileInputStream;

public class ExceptionDemo {

    public static void main(String[] args) {
       try {
            readFile();
        } catch (FileNotFoundException e) {
            System.out.println("Handled the FileNotFoundException");
        }
    }
    
    public static void readFile() throws FileNotFoundException {
        FileInputStream input = new FileInputStream("Location of file");
    }

}

If we does not use throws keyword or not handle the exception using try catch block then we get following suggestion from eclipse IDE. means we must handle Compile time Exception.

Let's see how we can throws multiple exception using throws keyword.

Example 5 :- throws multiple exception 

import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Date;

public class ExceptionDemo {

    public static void main(String[] args) {
        try {
            arithmeticOperation();
        } catch (Exception e) {
            e.printStackTrace();
            System.out.println("Handled the Exception");
        } catch (Exception e) {
            e.printStackTrace();
            System.out.println("Handled the Exception");
        }
    }
    
    public static void arithmeticOperation() throws ParseException, Exception{
        String date = new Date().toString();
        SimpleDateFormat format = new SimpleDateFormat();
        format.parse(date);
    }

}

Output :-
java.text.ParseException: Unparseable date: "Mon Jan 25 21:16:42 IST 2021"
    at java.base/java.text.DateFormat.parse(DateFormat.java:395)
    at ExceptionDemo.arithmeticOperation(ExceptionDemo.java:19)
    at ExceptionDemo.main(ExceptionDemo.java:9)
Handled the Exception
 

See other articles :-

• Java 8 Filter method with Examples
• Comparator in Java with examples 
• Spring Boot with Jpa, Mysql and Thymeleaf
• OOPS concepts in Java with Examples