如何制作对象的防御性副本？

Question

如何制作在不可变对象中包含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，并且永远不要更改。

Answer 1

您需要做的是

  MutableObject return_immutable_field() {
    return immutable_field;
  }

改成：

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

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