enum(枚舉)類介紹
**java枚舉類是一組預定義常量的集合，使用enum關鍵字聲明這個類，常量名稱官方建議大寫 **
1.enum類基本用法
舉一個常見的例子，例如星期就可以描述為一個枚舉類，如下
public enum Day {
SUNDAY, MONDAY, TUESDAY, WEDNESDAY,THURSDAY, FRIDAY, SATURDAY
}
怎么調用呢，Java switch語句參數就支持enum類
public class EnumTest {
Day day;
public EnumTest(Day day) {
this.day = day;
}
public void tellItLikeItIs() {
switch (day) {
case MONDAY:
System.out.println("周一各種不在狀態");
break;
case FRIDAY:
System.out.println("周五感覺還不錯");
break;
case SATURDAY: case SUNDAY:
System.out.println("周末給人的感覺是最棒的");
break;
default:
System.out.println("周內感覺就那樣吧。。。");
break;
}
}
public static void main(String[] args) {
EnumTest firstDay = new EnumTest(Day.MONDAY);
firstDay.tellItLikeItIs();
EnumTest thirdDay = new EnumTest(Day.WEDNESDAY);
thirdDay.tellItLikeItIs();
EnumTest fifthDay = new EnumTest(Day.FRIDAY);
fifthDay.tellItLikeItIs();
EnumTest sixthDay = new EnumTest(Day.SATURDAY);
sixthDay.tellItLikeItIs();
EnumTest seventhDay = new EnumTest(Day.SUNDAY);
seventhDay.tellItLikeItIs();
}
}
運行結果
EnumTest類運行結果.png
2.enum類和static常量區別
看了上面的例子，有些小伙伴就嗤之以鼻孔了，這沒什么嘛，java靜態常量也一樣可以辦到
public class EnumTest2 {
public static final int MONDAY= 1;
public static final int WEDNESDAY= 3;
public static final int FRIDAY= 5;
public static final int SATURDAY= 6;
public static final int SUNDAY= 7;
public void tellItLikeItIs(int day) {
switch (day) {
case 1:
System.out.println("周一各種不在狀態");
break;
case 5:
System.out.println("周五感覺還不錯");
break;
case 6: case 7:
System.out.println("周末給人的感覺是最棒的");
break;
default:
System.out.println("周內感覺就那樣吧。。。");
break;
}
}
public static void main(String[] args) {
EnumTest2 firstDay = new EnumTest2();
firstDay.tellItLikeItIs(MONDAY);
EnumTest2 thirdDay = new EnumTest2();
thirdDay.tellItLikeItIs(WEDNESDAY);
EnumTest2 fifthDay = new EnumTest2();
fifthDay.tellItLikeItIs(FRIDAY);
EnumTest2 sixthDay = new EnumTest2();
sixthDay .tellItLikeItIs(SATURDAY);
EnumTest2 seventhDay = new EnumTest2();
seventhDay.tellItLikeItIs(SUNDAY);
}
}
在這個使用方式效果上來看是沒有區別的，其實enum類的每一個枚舉值也是 static final的，但是我們為什么要選擇使用enum枚舉類呢
1.static方式的靜態變量類型不安全，我們可以在調用的時候傳入其他值，導致錯誤
例如： seventhDay.tellItLikeItIs(999);
2.static方式的靜態變量不支持屬性擴展，每一個key對應一個值，而enum的每一個key可以擁有自己的屬性
3.enum類自定義屬性
這就是enum比static靜態變量好用的地方了，可以賦予每一個枚舉值若干個屬性，例如
public enum Day {
MONDAY(1, "星期一", "星期一各種不在狀態"),
TUESDAY(2, "星期二", "星期二依舊犯困"),
WEDNESDAY(3, "星期三", "星期三感覺半周終于過去了"),
THURSDAY(4, "星期四", "星期四期待這星期五"),
FRIDAY(5, "星期五", "星期五感覺還不錯"),
SATURDAY(6, "星期六", "星期六感覺非常好"),
SUNDAY(7, "星期日", "星期日感覺周末還沒過夠。。。");
Day(int index, String name, String value) {
this.index = index;
this.name = name;
this.value = value;
}
private int index;
private String name;
private String value;
public int getIndex() {
return index;
}
public void setIndex(int index) {
this.index = index;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getValue() {
return value;
}
public void setValue(String value) {
this.value = value;
}
}
這次測試類就有些些變化了，更靈活了
public class EnumTest {
Day day;
public EnumTest(Day day) {
this.day = day;
}
public void tellItLikeItIs() {
switch (day) {
case MONDAY:
System.out.println(day.getName()+day.getValue());
break;
case FRIDAY:
System.out.println(day.getName()+day.getValue());
break;
case SATURDAY: case SUNDAY:
System.out.println(day.getName()+day.getValue());
break;
default:
System.out.println(day.getName()+day.getValue());
break;
}
}
public static void main(String[] args) {
EnumTest firstDay = new EnumTest(Day.MONDAY);
firstDay.tellItLikeItIs();
EnumTest thirdDay = new EnumTest(Day.WEDNESDAY);
thirdDay.tellItLikeItIs();
EnumTest fifthDay = new EnumTest(Day.FRIDAY);
fifthDay.tellItLikeItIs();
EnumTest sixthDay = new EnumTest(Day.SATURDAY);
sixthDay.tellItLikeItIs();
EnumTest seventhDay = new EnumTest(Day.SUNDAY);
seventhDay.tellItLikeItIs();
}
}
執行結果
EnumTest類運行結果.png
4.enum類高級玩法
你以為enum這樣就完了么，還有更好玩的東西，每一個enum枚舉值還可以擁有各自的內部方法！二話不說，上栗子
public enum Day {
MONDAY(1, "星期一", "各種不在狀態"){
@Override
public Day getNext() {
return TUESDAY;
}
},
TUESDAY(2, "星期二", "依舊犯困"){
@Override
public Day getNext() {
return WEDNESDAY;
}
},
WEDNESDAY(3, "星期三", "感覺半周終于過去了"){
@Override
public Day getNext() {
return THURSDAY;
}
},
THURSDAY(4, "星期四", "期待這星期五"){
@Override
public Day getNext() {
return FRIDAY;
}
},
FRIDAY(5, "星期五", "感覺還不錯"){
@Override
public Day getNext() {
return SATURDAY;
}
},
SATURDAY(6, "星期六", "感覺非常好"){
@Override
public Day getNext() {
return SUNDAY;
}
},
SUNDAY(7, "星期日", "感覺周末還沒過夠。。。"){
@Override
public Day getNext() {
return MONDAY;
}
};
Day(int index, String name, String value) {
this.index = index;
this.name = name;
this.value = value;
}
private int index;
private String name;
private String value;
public abstract Day getNext();
public int getIndex() {
return index;
}
public void setIndex(int index) {
this.index = index;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getValue() {
return value;
}
public void setValue(String value) {
this.value = value;
}
}
調用下看看
public class EnumTest {
Day day;
public EnumTest(Day day) {
this.day = day;
}
public void tellItLikeItIs() {
switch (day) {
case MONDAY:
System.out.println(day.getName()+day.getValue());
System.out.println(day.getName()+"的下一天是"+day.getNext().getName());
break;
case FRIDAY:
System.out.println(day.getName()+day.getValue());
System.out.println(day.getName()+"的下一天是"+day.getNext().getName());
break;
case SATURDAY: case SUNDAY:
System.out.println(day.getName()+day.getValue());
System.out.println(day.getName()+"的下一天是"+day.getNext().getName());
break;
default:
System.out.println(day.getName()+day.getValue());
System.out.println(day.getName()+"的下一天是"+day.getNext().getName());
break;
}
}
public static void main(String[] args) {
EnumTest firstDay = new EnumTest(Day.MONDAY);
firstDay.tellItLikeItIs();
EnumTest thirdDay = new EnumTest(Day.WEDNESDAY);
thirdDay.tellItLikeItIs();
EnumTest fifthDay = new EnumTest(Day.FRIDAY);
fifthDay.tellItLikeItIs();
EnumTest sixthDay = new EnumTest(Day.SATURDAY);
sixthDay.tellItLikeItIs();
EnumTest seventhDay = new EnumTest(Day.SUNDAY);
seventhDay.tellItLikeItIs();
}
}
執行結果
EnumTest類運行結果.png
5.參照文檔
http://docs.oracle.com/javase/tutorial/java/javaOO/enum.html
