面试-设计模式

写出单例模式代码并解决线程安全问题

package com.tensoflow;

public class SingletonDemo {

    // volatile解决多线程下数据同步问题
    private static volatile SingletonDemo instance;

    private SingletonDemo() {}

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