JAVA EXAMPLE PROGRAMS

JAVA EXAMPLE PROGRAMS

Publish Your Article Here

Program: How implement bounded types (extend superclass) with generics?


As of now we have seen examples for only one type parameter. What happens in case we want to access group of objects comes from same family, means extending same super class? You can restrict the generics type parameter to a certain group of objects which extends same super class. You can achieve this my specifying extends <super-class> at class definitions, look at the example, it gives you more comments to understand.


package com.java2novice.generics;

public class MyBoundedClassEx {

	public static void main(String a[]){
		//Creating object of sub class C and 
		//passing it to BoundEx as a type parameter.
		BoundEx<C> bec = new BoundEx<C>(new C());
		bec.doRunTest();
		//Creating object of sub class B and 
		//passing it to BoundEx as a type parameter.
		BoundEx<B> beb = new BoundEx<B>(new B());
		beb.doRunTest();
		//similarly passing super class A
		BoundEx<A> bea = new BoundEx<A>(new A());
		bea.doRunTest();
		//If you uncomment below code it will throw compiler error
		//becasue we restricted to only of type A and its sub classes.
		//BoundEx<String> bes = new BoundEx<String>(new String());
		//bea.doRunTest();
	}
}
/**
 * This class only accepts type parametes as any class
 * which extends class A or class A itself.
 * Passing any other type will cause compiler time error
 */
class BoundEx<T extends A>{
	
	private T objRef;
	
	public BoundEx(T obj){
		this.objRef = obj;
	}
	
	public void doRunTest(){
		this.objRef.printClass();
	}
}

class A{
	public void printClass(){
		System.out.println("I am in super class A");
	}
}

class B extends A{
	public void printClass(){
		System.out.println("I am in sub class B");
	}
}

class C extends A{
	public void printClass(){
		System.out.println("I am in sub class C");
	}
}

Output:
I am in sub class C
I am in sub class B
I am in super class A
<< Previous Program | Next Program >>
blog comments powered by Disqus

Java Generics Sample Code Examples

  1. Write a simple generics class example.
  2. Write a simple generics class example with two type parameters.
  3. How implement bounded types (extend superclass) with generics?
  4. How implement bounded types (implements an interface) with generics?
  5. What is generics wildcard arguments? Give an example.
Knowledge Centre
Domain Naming Service(DNS)
It is very difficult to remember a set of numbers (IP address) to connect to the Internet. The Domain Naming Service(DNS) is used to overcome this problem. It maps one particular IP address to a string of characters. For example, www.java2novice.com implies com is the domain name reserved for US commercial sites, java2novice is the name of the company and www is the name of the specific computer, which is java2novice's server.
Famous Quotations
When I do good, I feel good; when I do bad, I feel bad, and that is my religion.
-- Abraham Lincoln

About Author

Most Visited Pages

Other Interesting Sites

Reference: Java™ Platform Standard Ed. 7 - API Specification | Java is registered trademark of Oracle.
Privacy Policy | Copyright © 2017 by Nataraja Gootooru. All Rights Reserved.