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Program: How implement bounded types (implements an interface) 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 implementing same interface? You can restrict the generics type parameter to
a certain group of objects which implements same interface. You can achieve this my specifying extends <interface-name> at class
definitions, look at the example, it gives you more comments to understand. You can also specify multiple interfaces at the definision.
you can do this by specifying mulitple interfaces seperated by "&". You can also specify class which implements an interface and the interface
together. For example:
class MyClass<T extends TestClass & TestInterface> {
Look at example for more understanding.
package com.java2novice.generics;
public class MyBoundedInterface {
public static void main(String a[]){
//Creating object of implementation class X called Y and
//passing it to BoundExmp as a type parameter.
BoundExmp<Y> bey = new BoundExmp<Y>(new Y());
bey.doRunTest();
//Creating object of implementation class X called Z and
//passing it to BoundExmp as a type parameter.
BoundExmp<Z> bez = new BoundExmp<Z>(new Z());
bez.doRunTest();
//If you uncomment below code it will throw compiler error
//becasue we restricted to only of type X implementation classes.
//BoundExmp<String> bes = new BoundExmp<String>(new String());
//bea.doRunTest();
}
}
class BoundExmp<T extends X>{
private T objRef;
public BoundExmp(T obj){
this.objRef = obj;
}
public void doRunTest(){
this.objRef.printClass();
}
}
interface X{
public void printClass();
}
class Y implements X{
public void printClass(){
System.out.println("I am in class Y");
}
}
class Z implements X{
public void printClass(){
System.out.println("I am in class Z");
}
}
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| Output: |
I am in class Y
I am in class Z
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Java Generics Sample Code Examples
- Write a simple generics class example.
- Write a simple generics class example with two type parameters.
- How implement bounded types (extend superclass) with generics?
- How implement bounded types (implements an interface) with generics?
- What is generics wildcard arguments? Give an example.
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Interface and its usage
Interface is similar to a class which may contain method's signature only but not bodies and it is a formal set of method and constant
declarations that must be defined by the class that implements it. Interfaces are useful for declaring methods that one or more classes
are expected to implement, capturing similarities between unrelated classes without forcing a class relationship and determining an object's
programming interface without revealing the actual body of the class.
The very best thing you can do for the whole world is to make the most of yourself.
-- Wallace Wattles
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