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