初识枚举类，我们也许会提出疑问，枚举它是一种新的类型吗？不同于基本数据类型，引用
类型？？为了更好地理解，我们从反编译一个enum类开始：
原java代码
import java.util.Arrays;
import java.util.List;
public enum Weather {
Sunny(1, "晴天"), Rainy(2, "雨天"), Cloudy(3, "多云");
private int value;
private String label;
private Weather(int value, String label) {
this.value = value;
this.label = label;
}
public int getValue() {
return value;
}
public String getLabel() {
return label;
}
public static Weather parse(int value) {
Weather result = Weather.Sunny;
switch (value) {
case 1:
result = Weather.Sunny;
break;
case 2:
result = Weather.Rainy;
break;
case 3:
result = Weather.Cloudy;
break;
}
return result;
}
public static List getEnumValues() {
return Arrays.asList(values());
}
public static void main(String[] args) {
System.out.println(Weather.Sunny.getValue() + ":" + Weather.Sunny.getLabel());
Weather weather = Weather.Cloudy;
System.out.println(weather.getValue() + ":" + weather.getLabel());
List list = getEnumValues();
for (Weather sw : list) {
System.out.println(sw.value + "--" + sw.label);
}
}
}
反编译之后：
import java.io.PrintStream;
import java.util.*;
public final class Weather extends Enum{
private Weather(String s, int i, int value, String label){
super(s, i);
this.value = value;
this.label = label;
}
public int getValue(){
return value;
}
public String getLabel(){
return label;
}
public static Weather parse(int value){
Weather result = Sunny;
switch(value){
case 1: /*// '\001'*/
result = Sunny;
break;
case 2: /*// '\002'*/
result = Rainy;
break;
case 3: /*// '\003'*/
result = Cloudy;
break;
}
return result;
}
public static List getEnumValues(){
return Arrays.asList(values());
}
public static void main(String args[]){
System.out.println((new StringBuilder(String.valueOf(Sunny.getValue()))).append(":").append(Sunny.getLabel()).toString());
Weather weather = Cloudy;
System.out.println((new StringBuilder(String.valueOf(weather.getValue()))).append(":").append(weather.getLabel()).toString());
List list = getEnumValues();
Weather sw;
for(Iterator iterator = list.iterator(); iterator.hasNext(); System.out.println((new StringBuilder(String.valueOf(sw.value))).append("--").append(sw.label).toString()))
sw = (Weather)iterator.next();
}
public static Weather[] values(){
Weather aweather[];
int i;
Weather aweather1[];
System.arraycopy(aweather = ENUM$VALUES, 0, aweather1 = new Weather[i = aweather.length], 0, i);
return aweather1;
}
public static Weather valueOf(String s){
return (Weather)Enum.valueOf(Weather, s);
}
public static final Weather Sunny;
public static final Weather Rainy;
public static final Weather Cloudy;
private int value;
private String label;
private static final Weather ENUM$VALUES[];
static {
Sunny = new Weather(/*"Sunny", 0,*/ 1, "\u6674\u5929");
Rainy = new Weather(/*"Rainy", 1,*/ 2, "\u96E8\u5929");
Cloudy = new Weather(/*"Cloudy", 2,*/ 3, "\u591A\u4E91");
ENUM$VALUES = (new Weather[] {
Sunny, Rainy, Cloudy
});
}
}
通过观察代码我们会发现enum关键字的含义其实就是使类被final修饰并继承抽象类Enum，它是java枚举类型的公共基本类，里面提供了一些
公共方法，同时对象Sunny、Rainy、Cloudy都是使用static final修饰的不可变引用，他们在静态块中被用new的方式实例化并初始化。因此
得出结论：实际上枚举类型就是以Java类来实现的，没有什么新的特点，只不过java编译器帮我们做了语法的解析和编译。同时反编译之后，
代码中还自动生成了两个方法values()和valueOf(String name),这两个方法存在于
java.lang.annotation.ElementType
类下面：
valueOf(String name)返回指定枚举常量
values()返回枚举类型的数据，用于遍历枚举
public enum Test {
RED,YELLOW,GREEN,BLACK;
public static void main(String[] args) {
Test t[] = Test.values();
for (int i = 0; i < t.length; i++) {
System.out.println(t[i] + ":" + t[i].ordinal());
}
}
}
结果：
RED:0 YELLOW:1 GREEN:2 BLACK:3
通过反编译也可以看出，枚举类其实就是简单的java类构成的，不过它已经继承了Enum类，由于单继承特性，他不能再继承
其它类了，但可以实现接口。
以下是一个含有抽象方法的枚举类：
import java.util.Arrays;
import java.util.List;
public enum Weather {
Sunny(1, "晴天") {
@Override
public String test() {
return "今天阳光明媚！！！\n";
}
},
Rainy(2, "雨天") {
@Override
public String test() {
return "出门别忘带把雨伞哦！！！\n";
}
},
Cloudy(3, "多云") {
@Override
public String test() {
return "别出去登高望远了，你看不远的，呵呵呵！！！\n";
}
};
private int value;
private String label;
private Weather(int value, String label) {
this.value = value;
this.label = label;
}
public int getValue() {
return value;
}
public String getLabel() {
return label;
}
public abstract String test();
public static Weather parse(int value) {
Weather result = Weather.Sunny;
switch (value) {
case 1:
result = Weather.Sunny;
break;
case 2:
result = Weather.Rainy;
break;
case 3:
result = Weather.Cloudy;
break;
}
return result;
}
public static List getEnumValues() {
return Arrays.asList(values());
}
public static void main(String[] args) {
System.out.println(Weather.Sunny.getValue() + ":" + Weather.Sunny.getLabel());
Weather weather = Weather.Cloudy;
System.out.println(weather.getValue() + ":" + weather.getLabel() + "\n\n");
List list = getEnumValues();
for (Weather sw : list) {
System.out.println(sw.value + "--" + sw.label + "--" + sw.test());
}
}
}
反编译之后：
import java.io.PrintStream;
import java.util.*;
public abstract class Weather extends Enum {
private Weather(String s, int i, int value, String label) {
super(s, i);
this.value = value;
this.label = label;
}
public int getValue() {
return value;
}
public String getLabel() {
return label;
}
public abstract String test();
public static Weather parse(int value) {
Weather result = Sunny;
switch (value) {
case 1: // '\001'
result = Sunny;
break;
case 2: // '\002'
result = Rainy;
break;
case 3: // '\003'
result = Cloudy;
break;
}
return result;
}
public static List getEnumValues() {
return Arrays.asList(values());
}
public static void main(String args[]) {
System.out.println((new StringBuilder(String.valueOf(Sunny.getValue()))).append(":").append(Sunny.getLabel()).toString());
Weather weather = Cloudy;
System.out.println((new StringBuilder(String.valueOf(weather.getValue()))).append(":").append(weather.getLabel()).append("\n\n").toString());
List list = getEnumValues();
Weather sw;
for (Iterator iterator = list.iterator(); iterator.hasNext(); System.out.println((new StringBuilder(String.valueOf(sw.value))).append("--").append(sw.label).append("--").append(sw.test()).toString()))
sw = (Weather) iterator.next();
}
public static Weather[] values() {
Weather aweather[];
int i;
Weather aweather1[];
System.arraycopy(aweather = ENUM$VALUES, 0, aweather1 = new Weather[i = aweather.length], 0, i);
return aweather1;
}
public static Weather valueOf(String s) {
return (Weather) Enum.valueOf(Weather, s);
}
Weather(String s, int i, int j, String s1, Weather weather) {
this(s, i, j, s1);
}
public static final Weather Sunny;
public static final Weather Rainy;
public static final Weather Cloudy;
private int value;
private String label;
private static final Weather ENUM$VALUES[];
static {
Sunny = new Weather("Sunny", 0, 1, "\u6674\u5929") {
public String test() {
return "\u4ECA\u5929\u9633\u5149\u660E\u5A9A\uFF01\uFF01\uFF01\n";
}
};
Rainy = new Weather("Rainy", 1, 2, "\u96E8\u5929") {
public String test() {
return "\u51FA\u95E8\u522B\u5FD8\u5E26\u628A\u96E8\u4F1E\u54E6\uFF01\uFF01\uFF01\n";
}
};
Cloudy = new Weather("Cloudy", 2, 3, "\u591A\u4E91") {
public String test() {
return "\u522B\u51FA\u53BB\u767B\u9AD8\u671B\u8FDC\u4E86\uFF0C\u4F60\u770B\u4E0D\u8FDC\u7684\uFF0C\u5475\u5475\u5475\uFF01\uFF01\uFF01\n";
}
};
ENUM$VALUES = (new Weather[] { Sunny, Rainy, Cloudy });
}
}
由此可得出：
“不含抽象方法”的class反编译文件：public final class Weather extends Enum
“含有抽象方法”的class反编译文件：public abstract class Weather extends Enum