Java设计模式之单件模式深入讲解

public class Singleton{
	private static Singleton uniqueInstance; // 利用一个静态变量来记录Singleton类的唯一实例
	private Singleton(){} // 把构造器声明为私有的，只有自Singleton类内才可以调用构造器
	// 用getInstance()方法实例化对象，并返回这个实例
	public static Singleton getInstance(){
		if (uniqueInstance == null){
			uniqueInstance = new Singleton();
		}
		return uniqueInstance;
	}
}

public  class Singleton{
	private static Singleton uniqueInstance;

	private Singleton(){}

	public static synchronized Singleton getInstance(){
		if(uniqueInstance == null){
			uniqueInstance = new Singleton();
		}
		return uniqueInstance;
	}
}

public class Singleton{
	// 在静态初始化器（static initializai）中创建单件。这样可以保证线程安全（thread sate）
	private static Singleton uniqueInstance = new Singleton();

	private static Singleton getInstance(){
		return uniqueInstance;
	}
	
}

public class Singlenton{
	// volatile关键词：当uniqueInstance变量被初始化成Singleton实例时，多个线程正确地处理uniqueInstance变量
	private volatile static Singleton uniqueInstance();
	
	private Singleton(){}

	public static Singleton getInstance(){
		// 检查实例，如果不存在，就进入同步区块
		if(uniqueInstance == null){
			// 进入区块后，再检查一次。如果仍是null，才创建实例
			synchronized (Singleton.class){
				if(uniqueInstance == null){
					uniqueInstance = new Singleton();
				}
			}
		}
		return uniqueInstance;
	}
}

class Singleton:
	def getSingleton:
		pass
singleton = Singleton()

class Singleton(object):
    _instance = None
    def __new__(cls, *args, **kwargs):
        if cls._instance is None:
            cls._instance = object.__new__(cls, *args, **kwargs)
        return cls._instance
    def __init__(self):
        pass

def singleton(cls):
	# 创建一个私有变量，类型为字典，用来存放类地址的
    _instance = {}

    def inner():
    	# 如果类不存在
        if cls not in _instance:
        	# 实例化一个类并存放在字典里
            _instance[cls] = cls()
        return _instance[cls]
    return inner
    
@singleton
class ClassName(object):
    def __init__(self):
        pass

class Singleton(object):
    def __init__(self, cls):
        self._cls = cls # 接受类名
        self._instance = {} # 存放类地址
    def __call__(self):
        if self._cls not in self._instance:
        	# 实例化类并存放在字典内
            self._instance[self._cls] = self._cls()
        return self._instance[self._cls]

@Singleton
class ClassName(object):
    def __init__(self):
        pass