java枚举小结

1. 如何定义一个枚举类？

    //定义了4个等级
    enum Level{
        A，B，C，D
    }

2. 枚举类的实质：

    class Level{
        public static final Level A = new Level();
        public static final Level B = new Level();
        public static final Level C = new Level();
        public static final Level D = new Level();
    }

3. 枚举类可以定义构造方法，属性，方法

    enum Level{
        A("85~100","优"),
        B("75~84","良"),
        C("60~74","中"),
        D("60以下","差");
        private String score;
        private String ctype;
        private  Level(String score,String ctype){     //构造方法必须是私有的
            this.score = score ;
            this.ctype = ctype;
        }
        public String getscore(){
            return this.score;
        }
        public String getctpye(){
            return this.ctype;
        }
    }
    public class Enumation {
        public static void main(String[] args) {
            System.out.println(Level.A.getscore());
            System.out.println(Level.A.getctpye());
            Level[] ls = Level.values();
        }
    }
    //输出结果
    //85~100
    //优

4. 带抽象方法的枚举类

    enum Level{
        A("85~100"){
            @Override
            public String getctpye() {
                return "优";
            }
        },
        B("75~84") {
            @Override
            public String getctpye() {
                return "良";
            }
        },
        C("60~74") {
            @Override
            public String getctpye() {
                return "中";
            }
        },
        D("60以下") {
            @Override
            public String getctpye() {
                return "差";
            }
        };
        private String score;
        private  Level(String score){
            this.score = score ;
        }
        public String getscore(){
            return this.score;
        }
        public abstract String getctpye();  //每个对象都要重写抽象方法
    
    }

5. 常用方法

    public class Enumation {
        public static void main(String[] args) {
            System.out.println(Level.C.name()); //返回枚举常量的名称
            System.out.println(Level.C.ordinal()); //返回枚举常量的序号（下标从0开始）
            Level[] ls = Level.values();        //遍历枚举类型
            for(Level l :ls){
                System.out.println(l);
            }
            String letter = "B" ;
            //返回带指定名称的指定枚举类型的枚举常量，若letter为非枚举类型会抛异常java.lang.IllegalArgumentException: No enum constant
            Level b = Level.valueOf(letter);
            System.out.println(b.B);
        }
    }
   　　

   输出：
   C
   2
   A
   B
   C
   D
   B