单例设计模式的几种Java实现

一、静态变量初始化实现线程安全的单例模式

static变量instance是在类被加载时初始化并仅被初始化一次，这样就可以保证只有一个instance被初始化。

public class Singleton {
    private static Singleton instance = new Singleton();

    private Singleton(){}

    public static Singleton getInstance(){
        return instance;
    }

}

二、经典的非线程安全单例模式实现类

public class Singleton {
    private static Singleton instance;

    private Singleton(){ }

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

}

三、线程安全的单例模式实现类

public class Singleton {
    private static Singleton instance;

    private Singleton(){}

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

        return instance;
    }

}

四、高效的线程安全的单例模式实现类

public class Singleton {
    private static volatile Singleton instance;

    private Singleton(){}

    public static Singleton getInstance(){
        if(instance == null){
            //类锁
            synchronized(Singleton.class){
                if(instance == null){
                    instance = new Singleton();
                }
            }
        }

        return instance;
    }

}

写在最后：

以上是我工作中常遇到的单例模式实现方式，欢迎补充…