单例模式的三种写法

单例模式的三种写法：
1、懒汉式

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

2、饿汉式

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

3、新颖的写法

public class Singleton {   
  
  static class SingletonHolder {   
    static Singleton instance = new Singleton();   
  }   
  
  public static Singleton getInstance() {   
    return SingletonHolder.instance;   
  }   
  
}