Java 制作不可变的子类

Question

我有以下摘要class：

    public abstract class Client {

       final private String anonymousCilentID;
       final private String anonymousCilentFirstName;
       final private String anonymousCilentLastName;
       final private String gender;

            protected Client(String anonymousCilentID, String anonymousCilentFirstName, String anonymousCilentLastName, String gender) {
                this.anonymousCilentID = anonymousCilentID;
                this.anonymousCilentFirstName = anonymousCilentFirstName;
                this.anonymousCilentLastName = anonymousCilentLastName;
                this.gender = gender;
            }

        public String getAnonymousCilentID() {
            return anonymousCilentID;
        }

        public String getAnonymousCilentFirstName() {
            return anonymousCilentFirstName;
        }

        public String getAnonymousCilentLastName() {
            return anonymousCilentLastName;
        }

        public String getGender() {
            return gender;
        }
    }

和以下子class：

final public class AnonymousCilent extends Client {


   final private Date arrivalDate;
   final private String immStatus;
   final private Date registrationDate;
   final private String registrationSite;
   final private String siteName;
   final private String comments;



final public class AnonymousCilent extends Client {


   final private Date arrivalDate;
   final private String immStatus;
   final private Date registrationDate;
   final private String registrationSite;
   final private String siteName;
   final private String comments;

    public AnonymousCilent(String anonymousCilentID, String anonymousCilentFirstName, String anonymousCilentLastName, String gender, Date arrivalDate, String immStatus, Date registrationDate, String registrationSite, String siteName, String comments) {

        super(anonymousCilentID,anonymousCilentFirstName, anonymousCilentLastName, gender);

        this.arrivalDate = arrivalDate;
        this.immStatus = immStatus;
        this.registrationDate = registrationDate;
        this.registrationSite = registrationSite;
        this.siteName = siteName;
        this.comments = comments;
    }


    public Date getArrivalDate() {

        return new Date (arrivalDate.getTime());
    }

    public String getImmStatus() {
        return immStatus;
    }

    public Date getRegistrationDate() {
        return new Date (registrationDate.getTime());
    }

    public String getRegistrationSite() {
        return registrationSite;
    }

    public String getSiteName() {
        return siteName;
    }

    public String getComments() {
        return comments;
    }
}

我需要创建一个子class，但我想做的是制作不可变 classes 时的最佳实践。我将我的抽象构造函数设置为受保护，将我的变量声明为私有 final/no setter。我的 subclass 是不可变的吗？我做了一些不好的事情吗？如果是这样，我该如何解决？

Answer 1

你的classAnonymousCilent不是一成不变的，因为classjava.util.Date不是一成不变的。我可以这样做：

AnonymousCilent object = ...;

// Modifies the Date object held by the AnonymousCilent object
object.getArrivalDate().setDate(23);

为了防止这种情况，Date 对象的 getter 应该 return 成员变量的副本，例如：

public Date getArrivalDate() {
    // Return a copy of member variable arrivalDate
    return new Date(arrivalDate.getTime());
}

但是最好使用Java 8 java.time classes，它们是不可变的，而不是java.util.Date，或者使用Joda Time如果你没有使用 Java 8.

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