这个类是完全不可变的吗？

Question

我正在尝试按照Effective Java Item 15(Minimize Mutability)中给出的建议将可变类转换为Immutable类.谁能告诉我我创建的类是否完全不可变？

可变类

public class Record {
    public int sequenceNumber;
    public String id;
    public List<Field> fields;

    /**
     * Default Constructor
     */
    public Record() {
        super();
    }

    public Record addField(Field fieldToAdd) {
        fields.add(fieldToAdd);
        return this;
    }

    public Record removeField(Field fieldToRemove) {
        fields.remove(fieldToRemove);
        return this;
    }

    public int getSequenceNumber() {
        return sequenceNumber;
    }

    public String getId() {
        return id;
    }

    public List<Field> getFields() {
        return fields;
    }

    public void setSequenceNumber(int sequenceNumber) {
        this.sequenceNumber = sequenceNumber;
    }

    public void setFields(List<Field> fields) {
        this.fields = fields;
    }

    public void setId(String id) {
        this.id = id;
    }
}

实地班

public class Field {
    private String name;
    private String value;

    public Field(String name,String value) {
        this.name = name;
        this.value = value;
    }

    public String getName() {
        return name;
    }

    public String getValue() {
        return value;
    }
}

不变的阶级

public class ImmutableRecord {
    private final int sequenceNumber;
    private final String id;
    private final List<Field> fields;

    private ImmutableRecord(int sequenceNumber, List<Field> fields) {
        this.sequenceNumber = sequenceNumber;
        this.fields = fields;
        this.id = UUID.randomUUID().toString();
    }

    public static ImmutableRecord getInstance(int sequenceNumber, List<Field> fields) {
        return new ImmutableRecord(sequenceNumber, fields);
    }

    /********************* Only Accessor No Mutator *********************/

    public int getSequenceNumber() {
        return sequenceNumber;
    }

    public String getId() {
        return id;
    }

    public List<Field> getFields() {
        return Collections.unmodifiableList(fields);
    }

    /********************* Instance Methods *********************/

    public ImmutableRecord addField(Field fieldToAdd) {
        Field field = new Field(fieldToAdd.getName(), fieldToAdd.getValue());
        List<Field> newFields = new ArrayList<Field>(fields);
        newFields.add(field);
        Collections.unmodifiableList(newFields);
        ImmutableRecord immutableRecord = new ImmutableRecord(sequenceNumber, newFields);  
        return immutableRecord;
    }

    public ImmutableRecord removeField(Field fieldToRemove) {
        Field field = new Field(fieldToRemove.getName(), fieldToRemove.getValue());
        List<Field> newFields = new ArrayList<Field>(fields);
        newFields.remove(field);
        Collections.unmodifiableList(newFields);
        ImmutableRecord immutableRecord = new ImmutableRecord(sequenceNumber, newFields);  
        return immutableRecord;
    }
}

谢谢

谢卡尔

Answer 1

不可以,列表字段应该被复制而不是存储直接引用

private ImmutableRecord(int sequenceNumber, List<Field> fields) {
    this.sequenceNumber = sequenceNumber;
    this.fields = fields; // breaks immutability!!!
    this.id = UUID.randomUUID().toString();
}

如果某人修改了List字段引用,那么您的类也会反映它.在指定this.fields之前,最好将集合的内容复制到另一个集合中

此外,您的类似乎是可变的,因为它有添加和删除方法:)