面试手写-双重检查，搞定了吗？

女爷i 2022-09-14 09:49 201阅读 0赞

双重判断思路：先判断，再加锁，又在判断

public class SingletonDouble { 
        private static volatile SingletonDouble INSTANCE = null;
        private SingletonDouble(){ }
        public static SingletonDouble getInstance() { 
            // 第一次判断为空，则上锁；如果不为空，那么就直接return INSTANCE
            if (null == INSTANCE) { 
                synchronized (SingletonDouble.class) { 
                    // 第二次判断为空，则初始化
                    if (null == INSTANCE) { 
                        try { 
                        } catch (Exception e) { 
                            e.printStackTrace();
                        }
                        INSTANCE = new SingletonDouble();
                    }
                }
            }
            return INSTANCE;
        }
    
        //测试的不用管
        public static void main(String[] args) { 
            for (int i = 0; i < 100; i++) { 
                new Thread(() -> { 
                    System.out.println(SingletonDouble.getInstance().hashCode());
                }).start();
            }
        }
    }

更多文章已经被GitHub收录以及电子书等资料：[https://github.com/niutongg/JavaLeague][https_github.com_niutongg_JavaLeague]  
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![请添加图片描述][watermark_type_ZHJvaWRzYW5zZmFsbGJhY2s_shadow_50_text_Q1NETiBA54mb56ul5a2m6ZW_size_20_color_FFFFFF_t_70_g_se_x_16]

[https_github.com_niutongg_JavaLeague]: https://github.com/niutongg/JavaLeague
[watermark_type_ZHJvaWRzYW5zZmFsbGJhY2s_shadow_50_text_Q1NETiBA54mb56ul5a2m6ZW_size_20_color_FFFFFF_t_70_g_se_x_16]: /images/20220828/63b84e404e7045298e9057f40abe156f.png