Effective Java 第二版 Enum

Posted 2020-11-06 翔鹤岭

/**
 * Effective Java 第二版
 *   第30条：用enum代替int常量 
 */

import java.util.HashMap;
import java.util.Map;

public class EnumTest {

    /*媒体操作*/
    public final static int START = 1;
    public final static int PAUSE = 2;
    public final static int RESUME = 3;
    public final static int STOP = 4;

    /*返回结果*/
    public final static int RET_OK = 1;

    private static int playWithInt(int fun)
    {
        switch (fun)
        {
            case START:
            case PAUSE:
            case RESUME:
            case STOP:
                System.out.println("playWithInt do " + fun);
                break;
            default:
        }
        return RET_OK;
    }


    public enum PlayEm
    {
        START,PAUSE,RESUME,STOP //命名空间使得他可以重名
    }

    private static void playWithEnum(PlayEm fun)
    {
        switch (fun)
        {
            case START:
            case PAUSE:
            case RESUME:
            case STOP:
                System.out.println("playWithEnum do " + fun);
                break;
            default:

        }
    }

    public enum SuperPlayEm
    {
        START(1,"START"),PAUSE(2,"PAUSE"),RESUME(3,"RESUME"),STOP(4,"STOP");

        private final int code;
        private final String name;

        SuperPlayEm(int code, String name) {
            this.code = code;
            this.name = name;
        }

        @Override
        public String toString() {
            return "SuperPlayEm{" +
                    "code=" + code +
                    ", name=‘" + name + ‘\‘‘ +
                    ‘}‘;
        }

        public void doPlay(String player)
        {
            switch (this)
            {
                case START:
                case PAUSE:
                case RESUME:
                case STOP:
                    System.out.println("player : "+ player + " exec " + this.name());
                    break;
                default:
            }


        }
    }

    private static void playWithSuperEnum(SuperPlayEm fun)
    {
        switch (fun)
        {
            case START:
            case PAUSE:
            case RESUME:
            case STOP:
            default:
                System.out.println("playWithSuperEnum do " + fun);
        }
    }


    public enum SuperPlayApplyEm
    {
        START(1,"START"){void doPlay(String player){System.out.println("player : "+ player + " exec START" );}},
        PAUSE(2,"PAUSE"){void doPlay(String player){System.out.println("player : "+ player + " exec PAUSE" );}},
        RESUME(3,"RESUME"){void doPlay(String player){System.out.println("player : "+ player + " exec RESUME" );}},
        STOP(4,"STOP"){void doPlay(String player){System.out.println("player : "+ player + " exec STOP" );}};

        private final int code;
        private final String name;

        SuperPlayApplyEm(int code, String name) {
            this.code = code;
            this.name = name;
        }

        @Override
        public String toString() {
            return "SuperPlayEm{" +
                    "code=" + code +
                    ", name=‘" + name + ‘\‘‘ +
                    ‘}‘;
        }

        abstract void doPlay(String player);
    }

    public enum MixEnum
    {
        START("400100","1001"),
        PAUSE("400100","1002"),
        RESUME("400100","1003"),
        STOP("400100","1004")
        ;
        private final String baseCode;
        private final String followCode;

        private static final Map<String,MixEnum> map = new HashMap<String,MixEnum>();

        static {
            for (MixEnum mixEnum : MixEnum.values()) {
                map.put(mixEnum.baseCode+mixEnum.followCode,mixEnum);
            }
        }

        MixEnum(String baseCode, String followCode) {
            this.baseCode = baseCode;
            this.followCode = followCode;

        }

        public static MixEnum fromCode(String code)
        {
            return map.get(code);
        }
    }


    public static void main(String[] args) {
　　　　/*P128-P134*/

        //传统C做法
        playWithInt(START);  //打印无法识别
        playWithInt(RET_OK); //编译器不能报错

        //普通java枚举
        playWithEnum(PlayEm.START);
//        playWithEnum(RET_OK);


        /**
         * 自定义java枚举
         */
        SuperPlayEm aaa = SuperPlayEm.START;
        playWithSuperEnum(aaa);

        /**
         * 打印所有枚举信息
         * 如果有人要一份接口文档时，是不是会很好用
         */
        for (SuperPlayEm superPlayEm : SuperPlayEm.values()) {
            System.out.println(superPlayEm);
        }

        /**
         * 这个枚举可以做的很强大，给他设置很多参数，也可以定义函数
         * 但这样做可能在加一个枚举的时候，忘记加case分支
         */
        aaa.doPlay("camera");
        /**
         * 防止忘记加case
         * 但这样导致代码变多，各有利弊吧。
         */
        SuperPlayApplyEm superPlayApplyEm = SuperPlayApplyEm.PAUSE;
        superPlayApplyEm.doPlay("camera");

        /**
         * 生成枚举的方法 1  valueOf
         */
        SuperPlayEm superPlayEm = SuperPlayEm.valueOf("START");
        System.out.println(superPlayEm);

        /**
         * 生成枚举的方法 2   自定义
         *
         */
        MixEnum mixEnum = MixEnum.fromCode("4001001002");
        System.out.println(mixEnum);
    }

}