using throw : Specifying the Exceptions Thrown in a Method

throw statement is used to throw an exception inside a method.

Syntax

    throw ExceptionObject;

ExceptionObject is the any subclass of the class Throwable. Since Throwable is the super class for all the exceptions in java.

Example

class Stack{
 int size;
 
 Stack(int size){
  if(size < 0 )
   throw new NegativeArraySizeException("Stack size is less than zero");
  if(size == 0)
   throw new NegativeArraySizeException("Stack size is zero");
  this.size = size;
  System.out.println("Stack created with size " + size);
 }
}

   

class StackTest{
 public static void main(String args[]){
  Stack s1;
  
  try{
   s1 = new Stack(-10);
  }
  catch(Exception e){
   System.out.println(e);
  }
  
  try{
   s1 = new Stack(0);
  }
  catch(Exception e){
   System.out.println(e);
  }
  
  try{
   s1 = new Stack(10);
  }
  catch(Exception e){
   System.out.println(e);
  }
  
 }
}

Output

java.lang.NegativeArraySizeException: Stack size is less than zero
java.lang.NegativeArraySizeException: Stack size is zero
Stack created with size 10

Program, Stack.java has a single parameterized constructor, constructor checks for the size value, before initializing the size variable, if size is less than or equal to zero, then constructor, throw the exceptions with proper messages by using throw clause. StackTest.java tested the various scenarios.

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