泛型和类型安全

package com.isoftstone;

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

class? Apple{
private static long counter;
private final long id=counter++;
public long id()
{
return id;
}
}
class Orange{}
public class AppleandOrange {

/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
???? List<Apple> apples=new ArrayList<Apple>();
???? for(int i =0;i<3;i++)
???? {
??? apples.add(new Apple());
??? //apples.add(new Orange());
???? }
???? for(Apple a:apples)
???? {
??? System.out.println(a.id()) ;
??? System.out.println(a) ;//散列码的无符号十六进制
???? }
}

}

?