如何制作对象的防御性副本？ [英] How do I make defensive copy of an object?

问题描述

如何制作包含不可变对象中可变字段的Mutable对象的防御性副本？

How do I make defensive copies of a Mutable Object which contains a mutable field in an Immutable Object?

class ImmutableObject {

  private final MutableObject immutable_field;

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

class MutableObject {

  public int mutable_field;
}

• MutableObject没有允许的构造函数我设置了字段。


• MutableObject的当前状态应该在Immutable Object中捕获并且永远不会改变。



推荐答案

您需要做的是

  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

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