设计模式-单例模式

懒汉式:

//懒汉式单例类.在第一次调用的时候实例化自己 
//并发环境下很可能出现多个Singleton实例
public class Singleton {
    private Singleton() {}
    private static Singleton single=null;
    //静态工厂方法 
    public static Singleton getInstance() {
         if (single == null) {  
             single = new Singleton();
         }  
        return single;
    }
}

饿汉式:

//饿汉式单例类.在类初始化时，已经自行实例化 ,线程安全
public class Singleton1 {
    private Singleton1() {}
    private static final Singleton1 single = new Singleton1();
    //静态工厂方法 
    public static Singleton1 getInstance() {
        return single;
    }
}

双重检查锁定

public class Singleton {
    private Singleton() {}
    private static Singleton single=null;
    public static Singleton getInstance() {
        if (singleton == null) {  
            synchronized (Singleton.class) {  
               if (singleton == null) {  
                  singleton = new Singleton(); 
               }  
            }  
        }  
        return singleton; 
    }
}

静态内部类

public class Singleton {  
    private static class LazyHolder {  
       private static final Singleton INSTANCE = new Singleton();  
    }  
    private Singleton (){}  
    public static final Singleton getInstance() {  
       return LazyHolder.INSTANCE;  
    }  
}