java - 如何制作对象的防御性副本？

Question

如何制作包含不可变对象(immutable对象)中可变字段的可变对象的防御性副本？

class ImmutableObject {

  private final MutableObject immutable_field;

  ImmutableObject(MutableObject y) {
    this.immutable_field = y;
  }
}

class MutableObject {

  public int mutable_field;
}

• MutableObject 没有让我设置字段的构造函数。
• MutableObject 的当前状态应该在 Immutable Object 中捕获并且永远不会改变。

Answer 1

你需要做的就在

  MutableObject return_immutable_field() {
    return immutable_field;
  }

更改为:

  MutableObject return_immutable_field() {
    MutableObject tmp = new MutableObject();
    tmp.mutable_field = immutable_field.mutable_field;
    return tmp;
  }

有关解释，请参阅 http://www.javapractices.com/topic/TopicAction.do?Id=15