java常量定义方式

应该都会遇到在项目中定义一些常量，通常有三种实现方式：
a. 接口常量
b. 类常量
c. 枚举
我们一起了解下这几种

1. 接口常量

public interface SwingConstants {
    /**
     * The central position in an area. Used for
     * both compass-direction constants (NORTH, etc.)
     * and box-orientation constants (TOP, etc.).
     */
    int CENTER  = 0;


    /**
     * Box-orientation constant used to specify the top of a box.
     */
    int TOP     = 1;
    /**
     * Box-orientation constant used to specify the left side of a box.
     */
    int LEFT    = 2;

}

或者

public interface UtilConstants {
    /**
     * 公共常量
     */
    class Public {
        public static final String ID = "TESTID";
    }

    /**
     * JSP路径
     */
    class JspFilePath {
        public static final String TESTCONTROLLER = "jsp/basic/";
        public static final String TEMPLATE_PAGEPATH = "basic/template/"; // 模板（测试）
    }

    /**
     * vo 对象的一些公共的属性名称
     */
    class VoFields {
        public static final String ACTIONTIME = "operateTime";//操作时间
        public static final String ACTIONUSERNAME = "operatorName";//操作人姓名
        public static final String CHECKTIME = "auditTime";//审核时间
        public static final String CHECKUSERID = "checkUserId";//审核人ID
        public static final String CHECKUSERNAME = "auditPerson";//审核人姓名
        public static final String CREATETIME = "createTime";        // 创建时间
        public static final String CREATEUSERID = "createUserId";// 创建人code
        public static final String INSERTUSERNAME = "createUserName";// 创建人姓名
        public static final String UPDATETIME = "updateTime";        // 修改时间
        public static final String UPDATEUSERID = "updateUserId";// 修改人CODE
        public static final String UPDATEUSERNAME = "updateUserName";// 修改人姓名
        public static final String DELFLAG = "delFlag";             // 删除标记
        public static final String DBID = "dbid";                    // 主键
    }
}

优点：

• 简洁，不用写public static final

缺点：

• 需要看注释才能知道常量对应的信息
• 《Effective Java》这本书中提到过：如果某个实现了常量接口的类被修改不再需要常量了，也会因为序列化兼容原因不得不保持该实现，而且非final类实现常量接口会导致所有子类被污染

2. 类常量

public class ResponseCode {
    /** 系统处理正常 */
    public static final int SUCCESS_HEAD = 0;

    /** 系统处理未知异常 */
    public static final int EXCEPTION_HEAD = 1;

    /** JSON解析错误 */
    public static final int JSON_RESOLVE = 2;

    /** 类型不匹配 */
    public static final int TRANSTYPE_NO = 3;

    /** Head - messageID未赋值 */
    public static final int HEAD_messageID = 4;

    /** Head - timeStamp未赋值 */
    public static final int HEAD_timeStamp = 5;

    /** Head - messengerID未赋值 */
    public static final int HEAD_messengerID = 6;

    /** Head - transactionType 未赋值 */
    public static final int HEAD_transactionType = 7;

    /** digest校验不通过 */
    public static final int HEAD_DIGEST = 8;

    /** src校验不通过 */
    public static final int HEAD_SRC_NULL = 10;

    /** 协议包含非法字符 */
    public static final int ILLEGAL_MESSAGE = 11;

    /** 数据库异常 */
    public static final int DATABASE_EXCEPTION = 9;
    public static final Map<Integer, String> RESP_INFO = new HashMap<Integer, String>();

3. 枚举

public enum Size {
    SMALL("S"),
    MEDIUM("M"),
    LARGE("L"),
    EXTRA_LARGE("XL");

    /**
     * 缩写
     */
    private String suoxie;

    private Size(String suoxie){
        this.suoxie = suoxie;
    }

    public String getSuoxie(){
        return suoxie;
    }
}

4. 个人最推荐的方式: 类内枚举

public class Constants {
    public enum Dict{
        PROSTA("PROSTA","产品状态"),
        COUNTRY("COUNTRY","国家"),

        YWLX("YWLX","业务类型"),
        INDUSTRYCOMPANYTYPE("IndustryCompanyType","公司类型"),
        JSFS("JSFS","结算方式"),
        COMMISSIONTYPE("COMMISSIONTYPE","返佣类型"),
        BALUNITTYPE("BALUNITTYPE","结算单位类型"),
        ORDERSTATS("OrderStats","订单状态"),
        BACKORDERSTATUS("BackOrderStatus","退单审核状态"),
        BUSINESSPAYMENT("BusinessPayment","业务款项"),
        ENABLESTATE("enableState","启用禁用"),
        APPROVESTATE("approveState","审批状态"),
        //        分销系统所需是商品系统的xml
        PRODUCTCONTENTTYPE("productContentType","商品内容分类"),
        IDENTITY("identity","适应人群"),
        AREA("area","领区"),
        VISATYPE("visatype","签证类型"),
        SERVICETYPE("serviceType","公证认证商品内容分类"),
        PRODUCTTYPEQUALITY("productTypeQuality","公证认证商品性质"),
        EXPRESSTYPE("expresstype","公证认证加急种类"),
        IDETIFICATIONTYPE("identificationType","认证类别"),
        QYKHLX("QYKHLX","客户类型"),
        ZILIAONAME("ziliaoName","资料名称"),
        YESORNO("yesOrNo","是否");



        Dict(String value, String name){
            this.value=value;
            this.name=name;
        }
        private final String value;
        private final String name;

        public String getValue() {
            return value;
        }

        public String getName() {
            return name;
        }
    }
    /**
     * 订单状态
     * <p>Company:rayootech</p>
     * @author zhangxueshen
     * @date 2016-6-14
     */
    public enum OrderStats{

        DELETE(0,"删除"),RESERVE(1,"订单预定"),CONFIRM(2,"订单确认"),COMPLETE(3,"订单完成"),CLOSE(4,"订单关闭");

        OrderStats(Integer value, String name){
            this.value = value;
            this.name = name;
        }
        private final Integer value;
        private final String name;

        public Integer getValue() {
            return value;
        }

        public String getName() {
            return name;
        }

    }
}

作者 @没有故事的老大爷
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