Java单例内部类

发布于 2024-12-29 04:57:32 字数 639 浏览 4 评论 0原文

我知道Java中单例的概念。我在 Java 中创建单例作为内部类时遇到问题。问题发生在持有者的

public class NormalClass {
    private class Singleton {
        private static Singleton instance = null;

        private Singleton() {
        }

        private static class SingletonHolder {
            private static Singleton sessionData = new Singleton();
        }

        public static Singleton getInstance() {
            return NormalClass.Singleton.SingletonHolder.sessionData;
        }
    }

    public void method1() {
        Singleton.getInstance();
    }
}

错误是在 new Singleton() 构造函数调用时。如何正确调用 Singleton 的私有构造函数作为内部类？

问候

原文

I know the concept of singleton in Java.
I'm having problems with creating singleton as inner class in Java. Problem occurs at holder's

public class NormalClass {
    private class Singleton {
        private static Singleton instance = null;

        private Singleton() {
        }

        private static class SingletonHolder {
            private static Singleton sessionData = new Singleton();
        }

        public static Singleton getInstance() {
            return NormalClass.Singleton.SingletonHolder.sessionData;
        }
    }

    public void method1() {
        Singleton.getInstance();
    }
}

Error is at new Singleton() constructor call. How to proper call private constructor of Singleton as inner class?

Regards

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兰花执着 2025-01-05 04:57:32

如果它应该是真正的单例，请将您的单例类设为静态。然后你就可以调用构造函数了。

Java 嵌套类< 中解释了构造函数调用不起作用的原因/a> 教程。基本上，内部类需要外部类的实例才能构造：

private static Singleton sessionData = new NormalClass().new Singleton();

If it should be a real singleton, make your singleton class static. Then you will be able to call the constructor.

The reason why your constructor call does not work is explained in the Java nested classes tutorial. Basically, the inner class requires an instance of the outer class before it can be constructed:

private static Singleton sessionData = new NormalClass().new Singleton();

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菊凝晚露 2025-01-05 04:57:32

不能在非静态类中声明静态类。将 Singleton 类设为静态，一切都应该可以正常编译。

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吃→可爱长大的 2025-01-05 04:57:32

问题是内部类不是静态内部类，

public class NormalClass {
  private static class Singleton {
      private static Singleton instance = null;

      private Singleton() {
      }

      private static class SingletonHolder {
          private static Singleton sessionData = new Singleton();
      }

      public static Singleton getInstance() {
          return NormalClass.Singleton.SingletonHolder.sessionData;
      }
  }

  public void method1() {
      Singleton.getInstance();
  }
}

The problem is that the inner class is not static inner class,

public class NormalClass {
  private static class Singleton {
      private static Singleton instance = null;

      private Singleton() {
      }

      private static class SingletonHolder {
          private static Singleton sessionData = new Singleton();
      }

      public static Singleton getInstance() {
          return NormalClass.Singleton.SingletonHolder.sessionData;
      }
  }

  public void method1() {
      Singleton.getInstance();
  }
}

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清风无影 2025-01-05 04:57:32

按需初始化... Joshua Bloch ..

我认为如果你的内部类是静态的，那么你的持有者类也应该是静态的。

private static class SingletonHolder {
    static final Singleton instance = new Singleton();
}

或者为什么不喜欢这样呢？为什么要有内部持有者类别？

public class NormalClass{
  private static class InnerClass{
    private static InnerClass instance = null;
    private InnerClass(){}
    public static InnerClass getInstance() {
  if(null==NormalClass.InnerClass.instance){
    NormalClass.InnerClass.instance = new InnerClass(); 
  }
  return NormalClass.InnerClass.instance;
}
  }

  public void test(){
    InnerClass.getInstance();
  }
}

Initialize on Demand.... Joshua Bloch..

I think if your inner class is static, your holder class should also be static.

private static class SingletonHolder {
    static final Singleton instance = new Singleton();
}

Or Why not like this? why an inner holder class at all ?

public class NormalClass{
  private static class InnerClass{
    private static InnerClass instance = null;
    private InnerClass(){}
    public static InnerClass getInstance() {
  if(null==NormalClass.InnerClass.instance){
    NormalClass.InnerClass.instance = new InnerClass(); 
  }
  return NormalClass.InnerClass.instance;
}
  }

  public void test(){
    InnerClass.getInstance();
  }
}

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