Java Generics – Part5 – Generic methods - Sample Program

GenericClass.java

package com.codinko.generics;

public class GenericClass<T> {

	private T t;

	public T get() {
		return this.t;
	}

	public void set(T t) {
		this.t = t;
	}
}

GenericMethod1.java

package com.codinko.generics;

import java.util.ArrayList;
import java.util.Collection;
import java.util.List;

public class GenericMethod1 {

	// with wild card '?' this is not possible.
	// public static <?> addTooCollectionAndReturnElement(<?> element,
	// Collection<?> collection)// INVALID

	public <T> T addToCollectionAndReturnElement(T element, Collection<T> collection) {
		collection.add(element);
		return element;
	}

	// static method
	public static <T> T addToCollectionAndReturnElement2(T element, Collection<T> collection) {
		collection.add(element);
		return element;
	}

	public static void main(String[] args) {

		String name = "Harley";
		List<String> nameList = new ArrayList<String>();

		String nameElement = new GenericMethod1().<String> addToCollectionAndReturnElement(name, nameList);
		// We really don't need to specify the <String> type of teh generic method.
		//Compiler infer it. It's called type inference
		
		nameElement = new GenericMethod1().addToCollectionAndReturnElement(name, nameList);
		
		System.out.println(nameElement);

		Integer age = new Integer(25);
		List<Integer> ageList = new ArrayList<Integer>();

		Integer ageElement = addToCollectionAndReturnElement2(age, ageList);
		System.out.println(ageElement);

	}

}

GenericMethod2.java

package com.codinko.generics;

public class GenericMethod2 {


	//Generic Method
	public static <T> boolean isEqual(GenericClass<T> g1, GenericClass<T> g2) {
		return g1.get().equals(g2.get());
	}

	public static void main(String args[]) {

		GenericClass<String> obj1 = new GenericClass<String>();
		obj1.set("Harley");

		GenericClass<String> obj2 = new GenericClass<String>();
		obj2.set("Harley");

		boolean isEqual = GenericMethod2.<String> isEqual(obj1, obj2);
		isEqual = GenericMethod2.isEqual(obj1, obj2);
		System.out.println(isEqual);
		// This feature is called type inference. It allows you to invoke a
		// generic method as an
		// ordinary method, without specifying a type between angle brackets.
		// Compiler will infer the type that is needed
	}
}