泛型 深入理解

import java.util.*;

class Fruit { 	public String toString() {	return "Fruit"; } }

class Apple extends Fruit {	public String toString(){ return "Apple";	} }

class Person {	public String toString(){	return "Person";	} }

class ClassName<T> {//主类，把你文件名改成ClassName.java
	 

	 void show_1(T t){
		System.out.println("show_1  "+ t.toString());
	}
	
	<E> void show_2(E e){
		System.out.println("show_2  "+e.toString());
	}
	
	<T> void show_3(T t){
		System.out.println("show_3  "+t.toString());
	}
	
	

	public static void main(String[] args) {
		ClassName<Fruit> o = new ClassName<Fruit>();
		Fruit f = new Fruit();
		Apple a = new Apple();
		Person p = new Person();
		System.out.println("show_1 演示________________________");
		o.show_1( f );
		o.show_1( a );
//		o.show_1( p );  楼主把这行代码去掉注释看一下，是不能编译通过的。因为在
//		ClassName<Fruit>中已经限定了全局的T为Fruit，所以不能再加入Person;
		System.out.println("show_2 演示________________________");
		o.show_2( f );
		o.show_2( a );
		o.show_2( p );
		System.out.println("show_3 演示________________________");
		o.show_3( f );
		o.show_3( a );
		o.show_3( p );
		
	}
}
程序输出：
show_1 演示________________________
show_1  Fruit
show_1  Apple
show_2 演示________________________
show_2  Fruit
show_2  Apple
show_2  Person
show_3 演示________________________
show_3  Fruit
show_3  Apple
show_3  Person