03.单例模式-双重检测

/**
 * 单例模式-双重检测(推荐使用)
 * 1.构造私有
 * 2.静态代码块创建静态示例
 * 3.getInstance()方法公开
 */
public class SingleTon05 {
    //2.本类创建静态示例
    private static volatile SingleTon05 instance;

    //1.构造私有
    private SingleTon05() {
    }

    //3.getInstance()方法公开
    public static synchronized SingleTon05 getInstance() {
        if (instance == null){
            synchronized (SingleTon05.class){
                if(instance == null){
                    instance=new SingleTon05();
                }
            }
        }
        return instance;
    }
}