从优化的角度思考单例模式

从优化的角度思考单例模式

1. 懒汉模式的优化（synchronize解决线程安全问题）

   package design_mode;
   
   
   public class SingletonSynchronized {
   
   
       private  static  SingletonSynchronized singletonSynchronized = null;
   
       private SingletonSynchronized(){
           System.out.println("线程安全的单例模式");
       }
   
       public static SingletonSynchronized getSingletonSynchronized(){
           synchronized (SingletonSynchronized.class){
               if ((singletonSynchronized == null)){
                   singletonSynchronized = new SingletonSynchronized();
               }
               return singletonSynchronized;
           }
       }
   }
   

2. 双重锁认证进一步提高性能

   package design_mode;
   
   
   public class SingletonHight {
       private static SingletonHight singletonHight = null;
       private SingletonHight(){
           System.out.println("最终版单例模式");
       }
   
       public static SingletonHight getSingletonHight(){
           if(singletonHight==null){
               synchronized (SingletonHight.class){
                   if(singletonHight==null){
                       singletonHight = new SingletonHight();
                   }
   
               }
           }
           return singletonHight;
       }
   }
   

3. 通过静态内部类实现单例模式的延迟加载和线程安全

         这种方式是通过静态内部类实现的，静态内部类只有在调用时才会加载，这样就保证了延迟初始化，但是遇到序列化对象时会失效。

public class SingletonInnerObject {
    private SingletonInnerObject(){};
    
    private static class InnerObject {
        private static SingletonInnerObject singletonInnerObject = new SingletonInnerObject();
    }
    
    public static SingletonInnerObject getInstance(){
        return InnerObject.singletonInnerObject;
    }
}