Java中6种单例模式写法代码实例

public class Singleton {
    private static Singleton instance;
    private Singleton(){}

    public static synchronized Singleton getInstance(){ //synchronized锁住getInstance方法
        if (instance==null) {  //延迟加载
            instance = new Singleton();
        }
        return instance;
    }
}

public class Singleton {
    private volatile static Singleton instance; //volatile修饰实例
    private Singleton(){}
    public static  Singleton getInstance(){
        if (instance==null) {
            synchronized(Singleton.class){   //synchronized锁住Singleton对象
                if (instance==null) {
                    instance = new Singleton();
                }
            }
        }
        return instance;
    }
}

public class Singleton {
    private static Singleton instance = new Singleton(); //类加载时初始化静态实例
    private Singleton() {
    }
    public static Singleton getInstance() {
        return instance; //直接返回加载好的静态实例
    }
}

public class Singleton {
    private static Singleton instance = null;  

    static{                             
        instance = new Singleton();  //在静态代码块里初始化实例
    }

    private Singleton() {
    }

    public static Singleton getInstance() {

        return instance;
    }
}

public class Singleton {
    //定义静态内部类
    private static class InnerSingleton {
        private static final Singleton INSTANCE = new Singleton(); //初始化完成Singleton类静态实例
    }
    private Singleton() {
    }
    public static Singleton getInstance() {
        return InnerSingleton.INSTANCE; //返回静态内部类里的静态实例
    }
}

package acc;
public enum Singleton {
    INSTANCE; //定义1个唯一的成员INSTANCE
    //枚举类里的公共方法
    public  void  doSomething() {
        System.out.println("r2323t23");
    }
}
public class TestSingleton {
    public static void main(String[] args) {
        //使用枚举类.INSTANCE即可获取实例
        Singleton.INSTANCE.doSomething();
    }
}