Core JAVA

Handle exceptions in overriding methods in Java

There are few things to remember when overriding a method with exception handling. If super class method does not declare any exception, then sub class overridden method cannot declare checked exception but it can declare unchecked exceptions.

Example of Subclass overridden Method declaring Checked Exception

import java.io.*;
class Super
{
 void show() { 
   System.out.println("parent class"); 
   }
}

public class Sub extends Super 
{
 void show() throws IOException  //Compile time error   
  { 
    System.out.println("parent class"); 
  } 

 public static void main( String[] args )
 {
  Super s=new Sub();
  s.show();
 }  
}

As the method show() doesn’t throws any exception while in Super class, hence its overriden version can also not throw any checked exception.

Example of Subclass overriden Method declaring Unchecked Exception:

import java.io.*;
class Super
{
 void show(){ 
   System.out.println("parent class");
  }
}

public class Sub extends Super 
{
 void show() throws ArrayIndexOutOfBoundsException      //Correct
   { 
    System.out.println("child class"); 
   }

 public static void main(String[] args)
 {
  Super s=new Sub();
  s.show();
 }  
}

Because ArrayIndexOutOfBoundsException is an unchecked exception hence, overridden show() method can throw it.

More about Overridden Methods and Exceptions:

If Super class method throws an exception, then Subclass overridden method can throw the same exception or no exception, but must not throw parent exception of the exception thrown by Super class method.

It means, if Super class method throws object of NullPointerException class, then Subclass method can either throw same exception, or can throw no exception, but it can never throw object of Exception class (parent of NullPointerException class).

Example of Subclass overridden method with same Exception

import java.io.*;
class Super
{
 void show() throws Exception 
  {  
    System.out.println("parent class"); 
  }
}

public class Sub extends Super {
 void show() throws Exception  //Correct     
   { 
    System.out.println("child class");
   } 

 public static void main(String[] args)
 {
  try {
   Super s=new Sub();
   s.show();
   }
  catch(Exception e){}
 }  
}

Example of Subclass overriden method with no Exception:

import java.io.*;
class Super
{
 void show() throws Exception 
  {  
    System.out.println("parent class"); 
  }
}

public class Sub extends Super {
 void show()               //Correct     
   {
     System.out.println("child class"); 
   } 

 public static void main(String[] args)
 {
  try {
   Super s=new Sub();
   s.show();
   }
  catch(Exception e){}
 }  
}

Example of Subclass overriden method with parent Exception:

import java.io.*;
class Super
{
 void show() throws ArithmeticException 
  {  
   System.out.println("parent class");
  }
}

public class Sub extends Super {
 void show() throws Exception           //Cmpile time Error     
   { 
      System.out.println("child class");
   } 

 public static void main(String[] args)
 {
  try {
   Super s=new Sub();
   s.show();
   }
  catch(Exception e){}
 }  
}

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Dinesh Rajput

Dinesh Rajput is the chief editor of a website Dineshonjava, a technical blog dedicated to the Spring and Java technologies. It has a series of articles related to Java technologies. Dinesh has been a Spring enthusiast since 2008 and is a Pivotal Certified Spring Professional, an author of a book Spring 5 Design Pattern, and a blogger. He has more than 10 years of experience with different aspects of Spring and Java design and development. His core expertise lies in the latest version of Spring Framework, Spring Boot, Spring Security, creating REST APIs, Microservice Architecture, Reactive Pattern, Spring AOP, Design Patterns, Struts, Hibernate, Web Services, Spring Batch, Cassandra, MongoDB, and Web Application Design and Architecture. He is currently working as a technology manager at a leading product and web development company. He worked as a developer and tech lead at the Bennett, Coleman & Co. Ltd and was the first developer in his previous company, Paytm. Dinesh is passionate about the latest Java technologies and loves to write technical blogs related to it. He is a very active member of the Java and Spring community on different forums. When it comes to the Spring Framework and Java, Dinesh tops the list!

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