第三章之枚舉、注解

2019-01-22

內容：枚舉、注解

一、自定義一個枚舉類

public class TestSeason {

    public static void main(String[] args) {
        Season spring = Season.Spring;
        System.out.println(spring);
    }
}
public class Season {
    //將屬性定義為私有常量
    private final String seasonName;
    private final String seasonDes;
    
    //將構造器設置為私有的
    private Season (String seasonName, String seasonDes) {
        this.seasonName = seasonName;
        this.seasonDes = seasonDes;
    }
    //利用構造器構造春夏秋冬四個對象
    public static final Season Spring = new Season("春天","萬物復蘇");
    public static final Season Summer = new Season("夏天","驕陽似火");
    public static final Season Fall = new Season("秋天","秋高氣爽");
    public static final Season Winter = new Season("冬天","白雪皚皚");
    //因為屬性是常量，所以不能賦值
    public String getSeasonName() {
        return seasonName;
    }
    public String getSeasonDes() {
        return seasonDes;
    }
    //重寫toString方法
    @Override
    public String toString() {
        return "Season [seasonName=" + seasonName + ", seasonDes=" + seasonDes + "]";
    }
    
}

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二、通過關鍵字enum定義一個枚舉類并使用方法

public class TestSeason {

    public static void main(String[] args) {
        Season1 spring = Season1.Spring;
        System.out.println(spring);
        //使用values()方法將所有對象存入一個數組中
        Season1[] season = Season1.values();
        for (int i = 0; i < season.length; i++) {
            System.out.println(season[i]);
        }
        //使用valueOf(String name)方法將指定對象名的對象取出來
        String name = "Winter";
        Season1 winter = Season1.valueOf(name);
        System.out.println(winter);
    }
}
public enum Season1 {
    Spring("春天","萬物復蘇"),
    Summer("夏天","驕陽似火"),
    Fall("秋天","秋高氣爽"),
    Winter("冬天","白雪皚皚");
    
    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 + "]";
    }
    
}

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三、讓枚舉類實現一個接口，并且讓枚舉類的每個對象都重寫接口中的抽象方法

public class TestSeason {

    public static void main(String[] args) {
        Season1 spring = Season1.Spring;
        System.out.println(spring);
        //使用values()方法將所有對象存入一個數組中
        Season1[] season = Season1.values();
        for (int i = 0; i < season.length; i++) {
            System.out.println(season[i]);
        }
        //使用valueOf(String name)方法將指定對象名的對象取出來
        String name = "Winter";
        Season1 winter = Season1.valueOf(name);
        System.out.println(winter);
        //調用接口中的方法
        spring.Show();
    }
}
public interface Show {
    void Show();
}
public enum Season1 implements Show {
    Spring("春天","萬物復蘇"){
        @Override
        public void Show() {
            System.out.println("春天："+Spring.toString());
        }
    },
    Summer("夏天","驕陽似火"){
        @Override
        public void Show() {
            System.out.println("夏天："+Spring.toString());
        }
    },
    Fall("秋天","秋高氣爽"){
        @Override
        public void Show() {
            System.out.println("秋天："+Spring.toString());
        }
    },
    Winter("冬天","白雪皚皚"){
        @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 + "]";
    }
}

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四、JDK常用注釋
　　@Override:顯示表明方法重寫
　　@Deprecated:表明方法或者類過時，但依舊可以使用
　　@SuppressWarnings:抑制編譯器警告，即不讓編譯器發出警告
五、自定義注解
　　使用@interface
六、元注解
　　釋義：修飾注解的注解
　　@Retention:*用來指定某個Annotation存在的時間長短
????　　　　　　 *使用格式：@Retention(RetentionPolicy.成員變量)
??????　　　　　　　　　　　 @Retention(RetentionPolicy.SOURCE)表明該注釋在編譯時不會保留
?????? 　　　　　　　　　　　@Retention(RetentionPolicy.CLASS)表明在編譯時被記錄在.class文件中,運行不會保留，這是默認值
?????　　　　　　　　　　　? @Retention(RetentionPolicy.RUNTIME)表明在編譯時被記錄在.class文件中，運行時也保留，程序可以通過反射獲取該注釋
　　@Target:*用來指定某個Annotation能修飾的地方，默認是所有地方都能修飾
?　　　　　 ? *使用格式@Target(地方)，地方可以是FIELD,METHOD,CONSTRUCTION,TYPE,LOCAL_VARIABLE,PACKAGE,PARAMETER,ANNOTATION_TYPE中的任意個
　　@Documented:*用來指定某個Annotation在生成文檔的時候會被保留
???　　　　　　　　*格式：@Documented
　　@Inherited:*用來指定某個Annotation具有繼承性