Java 基础之枚举类及常见用法

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Java 枚举类（Enum）是一种特殊的数据类型，用于定义一组常量。

例如 web 请求状态码枚举类如下：

public enum ResultCode {

    /**
     * 请求成功状态码
     */
    SUCCESS(200, "成功"),

    /**
     * 请求失败状态码
     */
    FAIL(1000, "失败");

    private int code;
    private String msg;
    private static final Map<Integer, ResultCode> codeMsgMap = new HashMap<>();
    private static final Map<String, ResultCode> msgCodeMap = new HashMap<>();

    static {
        for (ResultCode resultCode : ResultCode.values()) {
            codeMsgMap.put(resultCode.getCode(), resultCode);
            msgCodeMap.put(resultCode.getMsg(), resultCode);
        }
    }

    ResultCode(int code, String msg){
        this.code = code;
        this.msg = msg;
    }
    public int getCode() {
        return code;
    }
    public String getMsg() {
        return msg;
    }

    public static Map<Integer, ResultCode> getCodeMsgMap() {
        return codeMsgMap;
    }
    public static Map<String, ResultCode> getMsgCodeMap() {
        return msgCodeMap;
    }

    public static ResultCode getMsgByCode(int code){
        for (ResultCode resultCode : ResultCode.values()) {
           if(resultCode.getCode() == code){
               return resultCode;
           }
        }
        return null;
    }
}

常见用法，一下列举出了枚举类的常见用法：

public class EmunTest {

    /**
     * 枚举类基本使用
     */
    @Test
    public void test1() {
        System.out.println(ResultCode.SUCCESS.getMsg() + ": " + ResultCode.SUCCESS.getCode());
    }

    /**
     * 枚举类遍历
     */
    @Test
    public void test2() {
        for (ResultCode resultCode : ResultCode.values()) {
            System.out.println("Code: " + resultCode.getCode());
            System.out.println("Message: " + resultCode.getMsg());
            System.out.println("--------------------------");
        }
    }

    /**
     * 测试自己写的 getByCode 方法获取枚举常量
     */
    @Test
    public void test3() {
        int code = 1000;
        ResultCode resultCode = ResultCode.getByCode(code);
        if (resultCode != null) {
            System.out.println(resultCode.getMsg() + ": " + resultCode.getCode());
        }
    }

    /**
     * 通过静态代码块，通过 map 获取枚举常量
     */
    @Test
    public void test4() {
        // 通过 code 获取枚举常量
        int code = 200;
        ResultCode resultCode = ResultCode.getCodeMsgMap().get(code);
        if (resultCode != null) {
            System.out.println(resultCode.getMsg() + ": " + resultCode.getCode());
        }

        // 通过 msg 获取枚举常量
        String msg = "失败";
        ResultCode resultCode2 = ResultCode.getMsgCodeMap().get(msg);
        if (resultCode2 != null) {
            System.out.println(resultCode2.getMsg() + ": " + resultCode2.getCode());
        }
    }
}

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