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Exception handling with method overriding in java


If the super class method does not declare an exception then subclass overridden method cannot declare the checked exception but it can declare unchecked exception.

If the super class method declares an exception then subclass overridden method can declare same exception, subclass exception or no exception but cannot declare parent exception of the exception thrown by super class method.

Example: If the super class method does not declare an exception then subclass overridden method cannot declare the checked exception.

ExceptionHandlingInOverriding1.java

import java.io.IOException;
 
/**
 * This program is used to show that If 
 * the super class method does not declare
 * an exception then subclass overridden 
 * method cannot declare the checked exception
 * @author codesjava
 */
 
class SuperClass{
	public void display(){
		System.out.println("Super class.");
	}
}
 
class SubClass extends SuperClass {
	//Compile time error here.
	public void display() throws IOException{
		System.out.println("Sub class.");
	}
}
public class ExceptionHandlingInOverriding1 {
	public static void main(String args[]){
		//Creating subclass object.
		SuperClass obj = new SubClass();
 
		//method call.
		obj.display();
	}
}

Output:

Exception in thread "main" java.lang.Error: 
Unresolved compilation problem:  
Exception IOException is not compatible with 
throws clause in SuperClass.display()

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Example: If the super class method does not declare an exception then subclass overridden method can declare unchecked exception.

ExceptionHandlingInOverriding2.java

/**
 * This program is used to show that 
 * If the super class method does not declare
 * an exception then subclass overridden 
 * method can declare the unchecked exception
 * @author codesjava
 */
 
class SuperClass{
	public void display(){
		System.out.println("Super class.");
	}
}
 
class SubClass extends SuperClass {
	//No Compile time error here.
	public void display() throws ArithmeticException{
		System.out.println("Sub class.");
	}
}
public class ExceptionHandlingInOverriding2 {
	public static void main(String args[]){
		//Creating subclass object.
		SuperClass obj = new SubClass();
 
		//method call.
		obj.display();
	}
}

Output:

Sub class.

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Example: If the super class method declares an exception then subclass overridden method can declare same exception.

ExceptionHandlingInOverriding3.java

/**
 * This program is used to show that 
 * If the super class method declares 
 * an exception then subclass overridden 
 * method can declare same exception.
 * @author codesjava
 */
 
class SuperClass{
	public void display()throws ArithmeticException{
		System.out.println("Super class.");
	}
}
 
class SubClass extends SuperClass {
	//can declare same exception.
	public void display() throws ArithmeticException{
		System.out.println("Sub class.");
	}
}
 
public class ExceptionHandlingInOverriding3 {
	public static void main(String args[]){
		//Creating subclass object.
		SuperClass obj = new SubClass();
 
		//method call.
		try {
			obj.display();
		} catch (Exception e) {
			System.out.println(e);
		}
	}
}

Output:

Sub class.

Download this example.

Example: If the super class method declares an exception then subclass overridden method can declare subclass exception.

ExceptionHandlingInOverriding4.java

/**
 * This program is used to show that 
 * If the super class method declares 
 * an exception then subclass overridden 
 * method can declare sub class exception.
 * @author codesjava
 */
 
class SuperClass{
	public void display()throws Exception{
		System.out.println("Super class.");
	}
}
 
class SubClass extends SuperClass {
	//can declare same exception.
	public void display() throws ArithmeticException{
		System.out.println("Sub class.");
	}
}
 
public class ExceptionHandlingInOverriding4 {
	public static void main(String args[]){
		//Creating subclass object.
		SuperClass obj = new SubClass();
 
		//method call.
		try {
			obj.display();
		} catch (Exception e) {
			System.out.println(e);
		}
	}
}

Output:

Sub class.

Download this example.

Example: If the super class method declares an exception then subclass overridden method can declare no exception.

ExceptionHandlingInOverriding5.java

/**
 * This program is used to show that 
 * If the super class method declares 
 * an exception then subclass overridden 
 * method can declare with no exception.
 * @author codesjava
 */
 
class SuperClass{
	public void display()throws Exception{
		System.out.println("Super class.");
	}
}
 
class SubClass extends SuperClass {
	//can declare with no exception.
	public void display(){
		System.out.println("Sub class.");
	}
}
 
public class ExceptionHandlingInOverriding5 {
	public static void main(String args[]){
		//Creating subclass object.
		SuperClass obj = new SubClass();
 
		//method call.
		try {
			obj.display();
		} catch (Exception e) {
			System.out.println(e);
		}
	}
}

Output:

Sub class.

Download this example.

Example: If the super class method declares an exception then subclass overridden method cannot declare parent exception.

ExceptionHandlingInOverriding6.java

/**
 * This program is used to show that 
 * If the super class method declares 
 * an exception then subclass overridden 
 * method cannot declare parent exception.
 * @author codesjava
 */
 
class SuperClass{
	public void display()throws ArithmeticException{
		System.out.println("Super class.");
	}
}
 
class SubClass extends SuperClass {
	//Compile time error here.
	public void display() throws Exception{
		System.out.println("Sub class.");
	}
}
 
public class ExceptionHandlingInOverriding6 {
	public static void main(String args[]){
		//Creating subclass object.
		SuperClass obj = new SubClass();
 
		//method call.
		try {
			obj.display();
		} catch (Exception e) {
			System.out.println(e);
		}
	}
}

Output:

Exception in thread "main" java.lang.Error: 
Unresolved compilation problem:
Exception Exception is not compatible with 
throws clause in SuperClass.display()

Download this example.
 
Next Topic: Custom exception in java with example.
Previous Topic: Exception propagation in java with example.

Related Topics:

Some important terms for Exception Handling.
Exception handling in java.
try and catch blocks in java with example.
Multiple catch blocks in java with example.
Nested try block in java with example.
Finally in java with example.
throw in java with example.
throws in java with example.
Exception propagation in java with example.
Exception handling with method overriding in java.
Custom exception in java with example.
Commonly used exception methods of Throwable class in java.

 

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