List中泛型的使用

import java.util.ArrayList;class Apple {private static long counter;private final long id = counter++;public long id() {return id;}}class Orange {}/** *  * 此处未使用泛型，当试图将orange对象转型为apple是，你就会得到一个语法错误； * @author hong.su * *///public class AppleandOrangeWithoutGenerics {//@SuppressWarnings("unchecked")//public static void main(String[] args){//ArrayList apple = new ArrayList();//for (int i = 0; i < 3; i++) {//apple.add(new Apple());//apple.add(new Orange());//for (int j = 0; j < apple.size(); j++) {//((Apple)apple.get(i)).id();//}//}//}//}public class AppleandOrangeWithoutGenerics{@SuppressWarnings("unchecked")public static void main(String[] args){ArrayList<Apple> apples = new ArrayList<Apple>();for (int i = 0; i < 3; i++) {apples.add(new Apple());for (int j = 0; j < apples.size(); j++) {System.out.println(apples.get(j).id());for (Apple c : apples) {System.out.println(c.id());}}}}}