帶有線程安全集合的Java類不可變

Question

假設我有以下課程：

public final class Person {

   final private String personFirstName;
   final private String personLastName;
   final private ConcurrentMap<Double, String> phoneMessages;

    public Person(String firstname, String lastname) {
       phoneMessages = new ConcurrentHashMap<Double, String>();
       this.personFirstName = firstname;
       this.personLastName = lastname;
    }

    public void add(Double key, String item) {
        phoneMessages.put(key, item);
    }

    public String getPersonFirstName() {
        return personFirstName;
    }

    public String getPersonLastName() {
        return personLastName;
    }

}

即使我創建了一個帶有私有最終線程安全集合的類，但我的類是不可變的嗎？ 我的猜測不是。

如果在對象中沒有集合是不正確的做法，那么Java中的正確做法是什么？ 我將如何設計包含集合的類？

Answer 1

正如其他人指出的那樣， 如何使用您的類將確定使其不可變是否合適。

也就是說，您的Person類的此版本是不可變的：

public final class Person {

   final private  String personFirstName;
   final private  String personLastName;
   final private ConcurrentMap<Double,String> phoneMessages;

    public Person(String firstname, String lastname) {
       this.phoneMessages = new ConcurrentHashMap<Double,String> ();
       this.personFirstName = firstname;
       this.personLastName  = lastname;
    }

    private Person(String firstname, String lastname, ConcurrentHashMap<Double,String> phoneMessages) {
       this.personFirstName = firstname;
       this.personLastName  = lastname;
       this.phoneMessages = phoneMessages;
    }

    public Person add(Double Key, String item){
        ConcurrentHashMap<Double, String> newMap = new ConcurrentHashMap<>(this.phoneMessages);
        newMap.put(Key, item);
        return new Person(this.personFirstName, this.personLastName, newMap);
    }

    public String getPersonFirstName() {
        return personFirstName;
    }

    public String getPersonLastName() {
        return personLastName;
    }

    public Map<Double, String> getPhoneMessages() {
        return Collections.unmodifiableMap(this.phoneMessages);
    }

}

注意， add方法返回一個不同的Person實例，以便當前的Person實例保持不變（不可變）。