Enum 枚举基础

１　定义一个枚举

enum Weekend {

    Monday,

    Tuesday,

    Wednesday,

    Thursday,

    Friday,

    Saturday,

    Sunday

}

 

 

２　得到每个枚举值

 for (Weekend weekend : Weekend.values())

 

３　返回枚举在集合中顺序（从０开始）

public final int ordinal() {

    return ordinal;

}

 

４　当前枚举名字

public final String name() {

    return name;

}

 

 

５　根据名字返回相应的enum实例

public static <T extends Enum<T>> T valueOf(Class<T> enumType,

                                            String name) {

    T result = enumType.enumConstantDirectory().get(name);

    if (result != null)

        return result;

    if (name == null)

        throw new NullPointerException("Name is null");

    throw new IllegalArgumentException(

        "No enum constant " + enumType.getCanonicalName() + "." + name);

}

 

 

６　怎么使用枚举

enum Weekend {

    Monday,

    Tuesday,

    Wednesday,

    Thursday,

    Friday,

    Saturday,

    Sunday

}



public class AppTest {

    Weekend weekend;



    public AppTest(Weekend weekend) {

        this.weekend = weekend;

    }



    public String toString() {

    return "the day is " + weekend;

    }



    public static void main(String[] args) {

        System.out.println(new AppTest(Weekend.Monday));

        System.out.println(new AppTest(Weekend.Tuesday));

        System.out.println(new AppTest(Weekend.Wednesday));

    }

}

 

７　枚举不能被继承（下面的代码报错，提示不能从final的test.Weekday继承）

enum WeekendSon extends Weekend {



}

 

 

８　定义enum构造函数

enum Step {
　　// Instances must be defined first, before methods:

    First("this is the first step"),

    Second("this is the second step"),

    Third("this is the third step"),

    Fourth("this is the fourth step");



    private String description;



    public String getDescription() {

        return description;

    }

    

    Step(String description) {

        this.description = description;

    }

}



public class AppTest {

    public static void main(String[] args) {

        for (Step step : Step.values()) {

            System.out.println(step + ":" + step.getDescription());

        }

    }

}

 

输出结果：

First:this is the first step

Second:this is the second step

Third:this is the third step

Fourth:this is the fourth step