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

public class TestSeason {

    public static void main(String[] args) {
        Season spring = Season.Spring;
        System.out.println(spring);
    }
}
public class Season {
    //将属性定义为私有常量
    private final String seasonName;
    private final String seasonDes;
    
    //将构造器设置为私有的
    private Season (String seasonName, String seasonDes) {
        this.seasonName = seasonName;
        this.seasonDes = seasonDes;
    }
    //利用构造器构造春夏秋冬四个对象
    public static final Season Spring = new Season("春天","万物复苏");
    public static final Season Summer = new Season("夏天","骄阳似火");
    public static final Season Fall = new Season("秋天","秋高气爽");
    public static final Season Winter = new Season("冬天","白雪皑皑");
    //因为属性是常量，所以不能赋值
    public String getSeasonName() {
        return seasonName;
    }
    public String getSeasonDes() {
        return seasonDes;
    }
    //重写toString方法
    @Override
    public String toString() {
        return "Season [seasonName=" + seasonName + ", seasonDes=" + seasonDes + "]";
    }
    
}

 

二、通过关键字enum定义一个枚举类并使用方法

public class TestSeason {

    public static void main(String[] args) {
        Season1 spring = Season1.Spring;
        System.out.println(spring);
        //使用values()方法将所有对象存入一个数组中
        Season1[] season = Season1.values();
        for (int i = 0; i < season.length; i++) {
            System.out.println(season[i]);
        }
        //使用valueOf(String name)方法将指定对象名的对象取出来
        String name = "Winter";
        Season1 winter = Season1.valueOf(name);
        System.out.println(winter);
    }
}
public enum Season1 {
    Spring("春天","万物复苏"),
    Summer("夏天","骄阳似火"),
    Fall("秋天","秋高气爽"),
    Winter("冬天","白雪皑皑");
    
    private final String seasonName;
    private final String seasonDes;
    
    private Season1 (String seasonName, String seasonDes) {
        this.seasonName = seasonName;
        this.seasonDes = seasonDes;
    }

    public String getSeasonName() {
        return seasonName;
    }
    public String getSeasonDes() {
        return seasonDes;
    }

    @Override
    public String toString() {
        return "Season1 [seasonName=" + seasonName + ", seasonDes=" + seasonDes + "]";
    }
    
}

 

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

public class TestSeason {

    public static void main(String[] args) {
        Season1 spring = Season1.Spring;
        System.out.println(spring);
        //使用values()方法将所有对象存入一个数组中
        Season1[] season = Season1.values();
        for (int i = 0; i < season.length; i++) {
            System.out.println(season[i]);
        }
        //使用valueOf(String name)方法将指定对象名的对象取出来
        String name = "Winter";
        Season1 winter = Season1.valueOf(name);
        System.out.println(winter);
        //调用接口中的方法
        spring.Show();
    }
}
public interface Show {
    void Show();
}
public enum Season1 implements Show {
    Spring("春天","万物复苏"){
        @Override
        public void Show() {
            System.out.println("春天："+Spring.toString());
        }
    },
    Summer("夏天","骄阳似火"){
        @Override
        public void Show() {
            System.out.println("夏天："+Spring.toString());
        }
    },
    Fall("秋天","秋高气爽"){
        @Override
        public void Show() {
            System.out.println("秋天："+Spring.toString());
        }
    },
    Winter("冬天","白雪皑皑"){
        @Override
        public void Show() {
            System.out.println("冬天："+Spring.toString());
        }
    };
    
    private final String seasonName;
    private final String seasonDes;
    
    private Season1 (String seasonName, String seasonDes) {
        this.seasonName = seasonName;
        this.seasonDes = seasonDes;
    }

    public String getSeasonName() {
        return seasonName;
    }
    public String getSeasonDes() {
        return seasonDes;
    }

    @Override
    public String toString() {
        return "Season1 [seasonName=" + seasonName + ", seasonDes=" + seasonDes + "]";
    }
}

 

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