单例模式+Java

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第一种饿汉模式

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

第二种静态内部类（lazy coding）

public class Singleton {      private static class SingletonHolder {      private static final Singleton INSTANCE = new Singleton();      }      private Singleton (){}      public static final Singleton getInstance() {      return SingletonHolder.INSTANCE;      }  }

第三种枚举

public enum Singleton {      INSTANCE;      public void whateverMethod() {      }  }

第四种双重校验锁

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;      }  }

构建单例的时候从以上四种方式选取即可。

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