重温设计模式（1）—— 单例模式

• 特点：整个应用中，单例类只存在一个对象
• 场景：应用参数类等
• 优点：节约内存，减少GC消耗
• 要点：私有化构造方法、线程安全
• 实现方案：
  • 静态初始化：class被加载时生成单例对象
    

    public class SimpleSingleton {
        
        private SimpleSingleton(){        
        }
        private static SimpleSingleton instance = new SimpleSingleton();
        
        public static SimpleSingleton getInstance() {
            return instance;
        }
    }

  • 内部类

    public class InnerSingleton {
        
        private InnerSingleton(){
            
        }
        
        public static InnerSingleton getInstance(){
            return SingletonInstance.instance;
        }
        
        private static class SingletonInstance{
            
            static InnerSingleton instance = new InnerSingleton();
            
        }
    }

  • 枚举：可序列化、防反射

    public enum Singleton {  
      
        INSTANCE;  
      
        private Singleton (){  
      
        }  
    }