枚舉的好處：

1. 類型安全性

2.使用方便性

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public class EnumDemo { enum Color{ RED(3),BLUE(5),BLACK(8),YELLOW(13),GREEN(28); private int colorValue; private Color(int rv){ this.colorValue=rv; } private int getColorValue(){return colorValue;} private int value(){return ordinal()+1;} } public static void main(String[] args) { for(Color s : Color.values()) { //enum的values()返回一個數組，這里就是Seasons[] System.out.println(s.value()+":"+s.name()+"="+s.getColorValue()); } } }

output：

1:RED=3
2:BLUE=5
3:BLACK=8
4:YELLOW=13
5:GREEN=28

其中，

/*** Returns the ordinal of this enumeration constant (its position* in its enum declaration, where the initial constant is assigned* an ordinal of zero).** Most programmers will have no use for this method. It is* designed for use by sophisticated enum-based data structures, such* as {@link java.util.EnumSet} and {@link java.util.EnumMap}.** @return the ordinal of this enumeration constant*/public final int ordinal() {return ordinal;}

?EnumMap是專門為枚舉類型量身定做的Map實現。雖然使用其它的Map實現（如HashMap）也能完成枚舉類型實例到值得映射，但是使用EnumMap會更加高效：它只能接收同一枚舉類型的實例作為鍵值，并且由于枚舉類型實例的數量相對固定并且有限，所以EnumMap使用數組來存放與枚舉類型對應的值。這使得EnumMap的效率非常高。

import java.util.*;public enum Phase {SOLID, LIQUID, GAS;public enum Transition {MELT(SOLID, LIQUID), FREEZE(LIQUID, SOLID), BOIL(LIQUID, GAS), CONDENSE(GAS, LIQUID), SUBLIME(SOLID, GAS), DEPOSIT(GAS, SOLID);private final Phase src;private final Phase dst;Transition(Phase src, Phase dst) {this.src = src;this.dst = dst;}private static final Map<Phase, Map<Phase, Transition>> m = new EnumMap<Phase, Map<Phase, Transition>>(Phase.class);static {for (Phase p : Phase.values())m.put(p, new EnumMap<Phase, Transition>(Phase.class));for (Transition trans : Transition.values())m.get(trans.src).put(trans.dst, trans);}public static Transition from(Phase src, Phase dst) {return m.get(src).get(dst);}}public static void main(String[] args) {for (Phase src : Phase.values())for (Phase dst : Phase.values())if (src != dst)System.out.printf("%s to %s : %s %n", src, dst,Transition.from(src, dst));} }

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轉載于:https://www.cnblogs.com/davidwang456/p/6138717.html

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