第三章之枚举、注解

2019-01-22

内容：枚举、注解

一、自定义一个枚举类

 1 public class TestSeason {
 2 
 3     public static void main(String[] args) {
 4         Season spring = Season.Spring;
 5         System.out.println(spring);
 6     }
 7 }
 8 public class Season {
 9     //将属性定义为私有常量
10     private final String seasonName;
11     private final String seasonDes;
12     
13     //将构造器设置为私有的
14     private Season (String seasonName, String seasonDes) {
15         this.seasonName = seasonName;
16         this.seasonDes = seasonDes;
17     }
18     //利用构造器构造春夏秋冬四个对象
19     public static final Season Spring = new Season("春天","万物复苏");
20     public static final Season Summer = new Season("夏天","骄阳似火");
21     public static final Season Fall = new Season("秋天","秋高气爽");
22     public static final Season Winter = new Season("冬天","白雪皑皑");
23     //因为属性是常量，所以不能赋值
24     public String getSeasonName() {
25         return seasonName;
26     }
27     public String getSeasonDes() {
28         return seasonDes;
29     }
30     //重写toString方法
31     @Override
32     public String toString() {
33         return "Season [seasonName=" + seasonName + ", seasonDes=" + seasonDes + "]";
34     }
35     
36 }

二、通过关键字enum定义一个枚举类并使用方法

 1 public class TestSeason {
 2 
 3     public static void main(String[] args) {
 4         Season1 spring = Season1.Spring;
 5         System.out.println(spring);
 6         //使用values()方法将所有对象存入一个数组中
 7         Season1[] season = Season1.values();
 8         for (int i = 0; i < season.length; i++) {
 9             System.out.println(season[i]);
10         }
11         //使用valueOf(String name)方法将指定对象名的对象取出来
12         String name = "Winter";
13         Season1 winter = Season1.valueOf(name);
14         System.out.println(winter);
15     }
16 }
17 public enum Season1 {
18     Spring("春天","万物复苏"),
19     Summer("夏天","骄阳似火"),
20     Fall("秋天","秋高气爽"),
21     Winter("冬天","白雪皑皑");
22     
23     private final String seasonName;
24     private final String seasonDes;
25     
26     private Season1 (String seasonName, String seasonDes) {
27         this.seasonName = seasonName;
28         this.seasonDes = seasonDes;
29     }
30 
31     public String getSeasonName() {
32         return seasonName;
33     }
34     public String getSeasonDes() {
35         return seasonDes;
36     }
37 
38     @Override
39     public String toString() {
40         return "Season1 [seasonName=" + seasonName + ", seasonDes=" + seasonDes + "]";
41     }
42     
43 }

三、让枚举类实现一个接口，并且让枚举类的每个对象都重写接口中的抽象方法

 1 public class TestSeason {
 2 
 3     public static void main(String[] args) {
 4         Season1 spring = Season1.Spring;
 5         System.out.println(spring);
 6         //使用values()方法将所有对象存入一个数组中
 7         Season1[] season = Season1.values();
 8         for (int i = 0; i < season.length; i++) {
 9             System.out.println(season[i]);
10         }
11         //使用valueOf(String name)方法将指定对象名的对象取出来
12         String name = "Winter";
13         Season1 winter = Season1.valueOf(name);
14         System.out.println(winter);
15         //调用接口中的方法
16         spring.Show();
17     }
18 }
19 public interface Show {
20     void Show();
21 }
22 public enum Season1 implements Show {
23     Spring("春天","万物复苏"){
24         @Override
25         public void Show() {
26             System.out.println("春天："+Spring.toString());
27         }
28     },
29     Summer("夏天","骄阳似火"){
30         @Override
31         public void Show() {
32             System.out.println("夏天："+Spring.toString());
33         }
34     },
35     Fall("秋天","秋高气爽"){
36         @Override
37         public void Show() {
38             System.out.println("秋天："+Spring.toString());
39         }
40     },
41     Winter("冬天","白雪皑皑"){
42         @Override
43         public void Show() {
44             System.out.println("冬天："+Spring.toString());
45         }
46     };
47     
48     private final String seasonName;
49     private final String seasonDes;
50     
51     private Season1 (String seasonName, String seasonDes) {
52         this.seasonName = seasonName;
53         this.seasonDes = seasonDes;
54     }
55 
56     public String getSeasonName() {
57         return seasonName;
58     }
59     public String getSeasonDes() {
60         return seasonDes;
61     }
62 
63     @Override
64     public String toString() {
65         return "Season1 [seasonName=" + seasonName + ", seasonDes=" + seasonDes + "]";
66     }
67 }

四、JDK常用注释
　　@Override:显示表明方法重写
　　@Deprecated:表明方法或者类过时，但依旧可以使用
　　@SuppressWarnings:抑制编译器警告，即不让编译器发出警告
五、自定义注解
　　使用@interface
六、元注解
　　释义：修饰注解的注解
　　@Retention:*用来指定某个Annotation存在的时间长短
    　　　　　　 *使用格式：@Retention(RetentionPolicy.成员变量)
      　　　　　　　　　　　 @Retention(RetentionPolicy.SOURCE)表明该注释在编译时不会保留
       　　　　　　　　　　　@Retention(RetentionPolicy.CLASS)表明在编译时被记录在.class文件中,运行不会保留，这是默认值
     　　　　　　　　　　　  @Retention(RetentionPolicy.RUNTIME)表明在编译时被记录在.class文件中，运行时也保留，程序可以通过反射获取该注释
　　@Target:*用来指定某个Annotation能修饰的地方，默认是所有地方都能修饰
 　　　　　   *使用格式@Target(地方)，地方可以是FIELD,METHOD,CONSTRUCTION,TYPE,LOCAL_VARIABLE,PACKAGE,PARAMETER,ANNOTATION_TYPE中的任意个
　　@Documented:*用来指定某个Annotation在生成文档的时候会被保留
   　　　　　　　　*格式：@Documented
　　@Inherited:*用来指定某个Annotation具有继承性