枚举方法覆盖 [英] Enum method overriding

问题描述

我发现 Enum 的定义如下：

  public Enum MyEnum {
 
 ONE 
 {
 @Override 
 public int getSomething（）{
 return 1; 
} 
}，
 
 TWO 
 {
 @Override 
 public int getSomething（）{
 return 2; 
} 
} 
 
 int getSomething（）
 {
 return 0; 
} 
} 
  

不知怎的，我觉得这种实现有些不舒服，因为我认为理想情况下应该为此目的定义一个字段，类应该看起来像：

  public Enum MyEnum {
 
 ONE（1），
 TWO（2）
 
 private int theSomething; 
 
 private MyEnum（int something）{
 theSomething = something; 
} 
 
 int getSomething（）
 {
 return theSomething; 
} 
} 
  

问题是除了个人不适之外我找不到任何好的理由改变这段代码。是否存在？

解决方案

（从注释中移除）

第一个例子通常用于实现Java中的有限状态机。它消除了每个方法必须有 if（state == FOO）{} else if（state == BAR） etc

> class MyFSM {

枚举状态{
FIRST_STATE {
@Override
void start fsm）{
fsm.doStart（）;
}
@Override
void stop（MyFSM fsm）{
throw new IllegalStateException（Not Started！）;
}
}，
SECOND_STATE {
@Override
void start（MyFSM fsm）{
throw new IllegalStateException（Already Started！
}
@Override
void stop（MyFSM fsm）{
fsm.doStop（）;
}
};

abstract void start（MyFSM fsm）;
abstract void stop（MyFSM fsm）;
}

private volatile状态state.FIRST_STATE;

public synchronized void start（）{
state.start（this）;
}

private void doStart（）{
state = SECOND_STATE;
}

public synchronized void stop（）{
state.stop（this）;
}

private void doStop（）{
state = FIRST_STATE;
}
}


I've found Enums defined like the following:

public Enum MyEnum {

   ONE
   {
      @Override
      public int getSomething() {
         return 1;
      } 
   },

   TWO
   {
      @Override
      public int getSomething() {
        return 2;
      }
   }

   int getSomething()
   {
      return 0;
   }
}

Somehow I feel some type of discomfort with this implementation because I would think that ideally a field should be defined for this purpose and the class should look something like:

public Enum MyEnum{

   ONE(1),
   TWO(2)

   private int theSomething;

   private MyEnum(int something) {
      theSomething = something;
   }

   int getSomething()
   {
      return theSomething;
   }
}

The problem is that apart from personal discomfort I cannot find any good reason to change this code. Do any exists?

解决方案

(moved from comment)

Your first example is used commonly to implement a finite state machine in Java. It eliminates the need for every method having to have a if (state == FOO) {} else if (state == BAR) etc

class MyFSM {

    enum State {
        FIRST_STATE {
            @Override
            void start(MyFSM fsm) {
                fsm.doStart();
            }
            @Override
            void stop(MyFSM fsm) {
                throw new IllegalStateException("Not Started!");
            }
        },
        SECOND_STATE {
            @Override
            void start(MyFSM fsm) {
                throw new IllegalStateException("Already Started!");
            }
            @Override
            void stop(MyFSM fsm) {
                fsm.doStop();
            }
        };

        abstract void start(MyFSM fsm);
        abstract void stop(MyFSM fsm);       
    }

    private volatile State state = State.FIRST_STATE;

    public synchronized void start() {
        state.start(this);
    }

    private void doStart() {
        state = SECOND_STATE;
    }

    public synchronized void stop() {
        state.stop(this);
    }

    private void doStop() {
        state = FIRST_STATE;
    }
}

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