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throw Vs throws Keyword in Java

Last Updated: 2 December, 2023

In Java, the keywords 'throw' and 'throws' are often used in the context of exception handling. Both keywords have different functionality and uses in Java programs.

In order to develop robust Java code, it is important to understand these keywords, their functions, and their uses in Java programs. Going forward, we will also see the difference between both keywords.

throw Keyword in Java

In Java, the 'throw' keyword is used to explicitly throw an exception (a user-defined or built-in exception) to the JVM. We can throw either checked or unchecked exceptions in Java by using the 'throw' keyword.

When an exception is explicitly thrown, the program execution flow transfers from the try block to the catch block.

The 'throw' keyword is used inside the method, and it is mainly used to throw custom (user-defined) exceptions. Using the throw keyword, only one exception-type object can be thrown at a time.

Syntax:

    
    throw new exception_class_name ("error message");
    
    // In another way, we create the object of the corresponding 
    // exception class and then throw an exception.
    
    exception_class_name expObject = new exception_class_name();
    throw expObject;

Example of "throw" keyword in Java

  public class ThrowWithUncheckedException {
    public static void validateRollNumber(int rollNumber) {
      if (rollNumber < 1) {
        // throwing Arithmetic exception if roll number is not valid
        throw new ArithmeticException("ERROR: Invalid Roll Number");
      } else {
        System.out.println("Roll Number is valid.");
      }
    }
  
    public static void main(String args[]) {
      // calling method for checking roll number is valid or invalid
      validateRollNumber(-10);
      System.out.println("Thank you...");
    }
  }

Output

Exception in thread "main" java.lang.ArithmeticException: ERROR: Invalid Roll Number at com.javabytechie.throwkeyword.ThrowWithUncheckedException.validateRollNumber(ThrowWithUncheckedException.java:7) at com.javabytechie.throwkeyword.ThrowWithUncheckedException.main(ThrowWithUncheckedException.java:15)

throws Keyword in Java

In Java, the 'throws' keyword is used in a method signature and declares which exceptions can be thrown from a method.

Exceptions can be propagated in the call stack using the 'throws' keyword. When a method declares that it throws an exception, it is not required to handle the exception. The caller of a method that throws exceptions is required to handle the exceptions (or throw them to its caller, and so on) so that the flow of the program can be maintained.

The 'throws' keyword enables us to declare multiple exceptions; if we do so, a comma should separate each exception in the declaration.

Throws only handle checked exceptions. Unchecked exceptions do not need to be thrown or handled explicitly in code.

Syntax:

  return_type method_name (arguments) throws Exception1, Exception2, … {  }

Example of "throws" keyword

  public class ThrowsExample1 {
    public static void calculate() throws ArithmeticException, ArrayIndexOutOfBoundsException {
      int num[] = { 10, 20 };
      System.out.println("Division Result: " + num[0] / 2);
      System.out.println("Division Result: " + num[5] / 2);
    }
  
    public static void main(String[] args) {
      try {
        calculate();
      } catch (ArithmeticException e) {
        System.out.println("Arithmetic Exception thrown" + e.getMessage());
      } catch (ArrayIndexOutOfBoundsException e) {
        System.out.println("ArrayIndexOutOfBounds Exception thrown" + e.getMessage());
      }
    }
  }

Output

Division Result: 5
ArrayIndexOutOfBounds Exception thrownIndex 5 out of bounds for length 2

Difference between 'throw' and 'throws' keywords in Java

throw	throws
The 'throw' keyword is used to throw an exception object explicitly.	The 'throws' keyword is used to declare an exception as well as bypass the caller.
'throw' allows us to declare only one exception at a time.	'throws' allow us to declare multiple exceptions at a time.
'throw' is used inside the method body.	'throws' is used with the method signature.
'throw' is followed by an instance.	'throws' is followed by a class name.
Only unchecked exceptions can be propagated using the 'throw' keyword.	'throws' keyword can be used to propagate checked exceptions only.
Example: throw new StudentRecordNotFound(“Student record is not available.”);	Example: throws IOException, ArrayIndexBoundException;

That's all guys, hope this Java article is helpful for you.

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throw Vs throws Keyword in Java

throw Keyword in Java

throws Keyword in Java

Difference between 'throw' and 'throws' keywords in Java

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