单利模式-singleton

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public class Singleton {  
    private static EagerSingleton instance = new EagerSingleton();
    private Singleton() { //私有构造函数  }    
    public static EagerSingleton getInstance()
    {
        return instance;
    }    
}

public class SingletonClass{
        private static SingletonClass instance=null;
        private SingletonClass(){}
        public static SingletonClass getInstance(){
        if(instance==null){
           instance=new SingletonClass();
            }
        }
        return instance;
        }
    }

public class SingletonClass{
        private static SingletonClass instance=null;
        private SingletonClass(){}
        public static synchronized SingletonClass getInstance(){
        if(instance==null){
           instance=new SingletonClass();
            }
        }
        return instance;
        }
    }

public class SingletonClass{
        private static SingletonClass instance=null;
        private SingletonClass(){}
        public static SingletonClass getInstance(){
        if(instance==null){
            synchronized(SingletonClass.class){
            if(instance==null){
                instance=new SingletonClass();
            }
            }
        }
        return instance;
        }
    }

单利模式-singleton

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原文地址：http://my.oschina.net/u/1989867/blog/528151