如何制作对象的防御性副本？

Question

如何制作包含不可变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没有允许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

你需要做的是在

  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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