设计模式-单例模式

public class LazySingleton {
    //保证 instance 在所有线程中同步
    private static volatile LazySingleton instance=null;
    //避免类在外部被实例化
    private LazySingleton(){}

    public static synchronized LazySingleton getInstance() {
        //getInstance 方法前加同步
        if(instance==null) {
            instance=new LazySingleton();
        }
        return instance;
    }
}

public class HungrySingleton {
    private static final HungrySingleton instance=new HungrySingleton();
    private HungrySingleton(){}
    public static HungrySingleton getInstance()
    {
        return instance;
    }
}