无法理解java中的枚举

Question

我正在查看本书中提供的示例代码

enum Coin
{
   PENNY(1),
   NICKEL(5),
   DIME(10),
   QUARTER(25);

   private final int denomValue;

   Coin(int denomValue)
   {
      this.denomValue = denomValue;
   }

   int denomValue()
   {
      return denomValue;
   }

   int toDenomination(int numPennies)
   {
      return numPennies / denomValue;
   }
}

public class Coins
{
   public static void main(String[] args)
   {
      if (args.length == 1)
      {
         int numPennies = Integer.parseInt(args[0]);
         System.out.println(numPennies + " pennies is equivalent to:");
         int numQuarters = Coin.QUARTER.toDenomination(numPennies);
         System.out.println(numQuarters + " " + Coin.QUARTER.toString() +
                            (numQuarters != 1 ? "s," : ","));
         numPennies -= numQuarters * Coin.QUARTER.denomValue();
         int numDimes = Coin.DIME.toDenomination(numPennies);
         System.out.println(numDimes + " " + Coin.DIME.toString() +
                            (numDimes != 1 ? "s, " : ","));
         numPennies -= numDimes * Coin.DIME.denomValue();
         int numNickels = Coin.NICKEL.toDenomination(numPennies);
         System.out.println(numNickels + " " + Coin.NICKEL.toString() +
                            (numNickels != 1 ? "s, " : ", and"));
         numPennies -= numNickels*Coin.NICKEL.denomValue();
         System.out.println(numPennies + " " + Coin.PENNY.toString() +
                            (numPennies != 1 ? "s" : ""));
      }
      System.out.println();
      System.out.println("Denomination values:");
      for (int i = 0; i < Coin.values().length; i++)
         System.out.println(Coin.values()[i].denomValue());
   }
}  

如果enum就像一个类,是否可以为类中的方法和字段使用相同的名称,因为这里使用denomValue完成了？

为什么这样打电话int numQuarters = Coin.QUARTER.toDenomination(numPennies);？toDenomination()默认是静态的吗？

在上面的例子中,denomValue字段的值是多少？该程序的输出提示它应该等于QUARTER.但是这有什么作用呢？Coin.QUARTER相当于创建一个硬币对象并传递QUARTER作为它的构造函数参数吗？

Answer 1

每一个PENNY,NICKEL都是实例Coin类是静态的,所以它们可以作为进行访问Coin.PENNY.

所以当你这样做时:

Coin.QUARTER.toDenomination(numPennies)

您正在访问QUARTERcoin类的实例并调用其toDenomination()方法,该方法是在实例上调用的实例方法QUARTER.

当你这样做时:

PENNY(1) //this actually calls the constructor with one integer argument of Coin class

要检查PENNY是否是Coin类的实例:

System.out.println(Coin.PENNY.getClass());  //Will show you Coin