double checked locking单例模式

/**
 * double checked locking
 */
public class Singleton {
    private Singleton() {

    }
    private static volatile Singleton instance = null;

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

为甚么这样做？

避免synchronized 内过多代码块,从而影响效率。

为甚么要加volatile？

避免指令重排从而影响到代码准确性。

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标签：Singleton,checked,synchronized,double,locking,private,instance,static,null
来源： https://www.cnblogs.com/coding8832/p/14475259.html