单例模式概念
- 一个类只能有一个实例
- 由自己创建的唯一实例
- 给其他对象提供这一实例
应用场景
- 建立数据库连接
- 计数器
- 唯一序列号
实现案例
- 类加载时初始化,多线程安全
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public class Singleton { private static Singleton instance = new Singleton(); private Singleton (){} public static Singleton getInstance() { return instance; } }
- 初始化懒加载模式，多线程安全
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public class Singleton { private static class SingletonHolder { private static final Singleton INSTANCE = new Singleton(); } private Singleton (){} public static final Singleton getInstance() { return SingletonHolder.INSTANCE; } }
- 防止反序列化重新创建的枚举类型,多线程安全
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public enum Singleton { INSTANCE; public void method() { } }
- 初始化懒加载，双锁机制，多线程情况下能保持高性能
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public class Singleton { private volatile static Singleton singleton; private Singleton (){} public static Singleton getSingleton() { if (singleton == null) { synchronized (Singleton.class) { if (singleton == null) { singleton = new Singleton(); } } } return singleton; } }