1. 单例模式

/**  限制对象个数的单例模式    */
public class Emperor {

private static int maxNum = 2;    // 对象最大个数
private static ArrayList<Emperor> emperors = new ArrayList<Emperor>();   // 类内部提供对象存储list
private String name;

static{
for (int i = 0; i < maxNum; i++) {
emperors.add(new Emperor(i+"emperor"));
}
}

private Emperor(String name){this.name = name;}

public static Emperor getInstance(){
int i = new Random().nextInt(2);
return emperors.get(i);
}
}