做应用系统时，我们往往假设用户是小白，那么为了保证系统的正常，我们往往会对用户的参数做限制，并且前后端都要对用户的参数做验证。那我们在设计的时候是否可以提前预防这种问题呢？其中的一种方式就是：用枚举enum替代int常量。
枚举的好处：
做应用系统时，我们往往假设用户是小白，那么为了保证系统的正常，我们往往会对用户的参数做限制，并且前后端都要对用户的参数做验证。那我们在设计的时候是否可以提前预防这种问题呢？其中的一种方式就是：用枚举enum替代int常量。
枚举的好处：
1. 类型安全性
2.使用方便性
示例1
<pre spellcheck="false" style="box-sizing: border-box; margin: 5px 0px; padding: 5px 10px; border: 0px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-variant-numeric: inherit; font-variant-east-asian: inherit; font-weight: 400; font-stretch: inherit; font-size: 16px; line-height: inherit; font-family: inherit; vertical-align: baseline; cursor: text; counter-reset: list-1 0 list-2 0 list-3 0 list-4 0 list-5 0 list-6 0 list-7 0 list-8 0 list-9 0; background-color: rgb(240, 240, 240); border-radius: 3px; white-space: pre-wrap; color: rgb(34, 34, 34); letter-spacing: normal; orphans: 2; text-align: left; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">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()返回一个数组，这里就是Seasons[]
System.out.println(s.value()+":"+s.name()+"="+s.getColorValue());
}
}
}
</pre>
output：
1:RED=3
2:BLUE=5
3:BLACK=8
4:YELLOW=13
5:GREEN=28
其中
<pre spellcheck="false" style="box-sizing: border-box; margin: 5px 0px; padding: 5px 10px; border: 0px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-variant-numeric: inherit; font-variant-east-asian: inherit; font-weight: 400; font-stretch: inherit; font-size: 16px; line-height: inherit; font-family: inherit; vertical-align: baseline; cursor: text; counter-reset: list-1 0 list-2 0 list-3 0 list-4 0 list-5 0 list-6 0 list-7 0 list-8 0 list-9 0; background-color: rgb(240, 240, 240); border-radius: 3px; white-space: pre-wrap; color: rgb(34, 34, 34); letter-spacing: normal; orphans: 2; text-align: left; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;"> /**
* 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;
}
</pre>
示例2：
EnumMap是专门为枚举类型量身定做的Map实现。虽然使用其它的Map实现（如HashMap）也能完成枚举类型实例到值得映射，但是使用EnumMap会更加高效：它只能接收同一枚举类型的实例作为键值，并且由于枚举类型实例的数量相对固定并且有限，所以EnumMap使用数组来存放与枚举类型对应的值。这使得EnumMap的效率非常高。
<pre spellcheck="false" style="box-sizing: border-box; margin: 5px 0px; padding: 5px 10px; border: 0px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-variant-numeric: inherit; font-variant-east-asian: inherit; font-weight: 400; font-stretch: inherit; font-size: 16px; line-height: inherit; font-family: inherit; vertical-align: baseline; cursor: text; counter-reset: list-1 0 list-2 0 list-3 0 list-4 0 list-5 0 list-6 0 list-7 0 list-8 0 list-9 0; background-color: rgb(240, 240, 240); border-radius: 3px; white-space: pre-wrap; color: rgb(34, 34, 34); letter-spacing: normal; orphans: 2; text-align: left; text-indent: 0px; text-transform: none; widows: 2; word-spacing: 0px; -webkit-text-stroke-width: 0px; text-decoration-style: initial; text-decoration-color: initial;">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));
}
}
</pre>
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