java - 从继承的 protected Java 字段创建公共(public)访问器

Question

我怎样才能完成以下工作:

class Foo extends javax.swing.undo.UndoManager {
  // increase visibility - works for method
  override def editToBeUndone: javax.swing.undo.UndoableEdit = super.editToBeUndone

  // fails for field
  def edits: java.util.Vector[javax.swing.undo.UndoableEdit] = super.edits
}

请注意，edits 是 CompoundEdit(UndoManager 的父类(super class))中的 protected 字段。我想要一个读取该字段的同名公共(public)访问器。我该怎么做？

<console>:8: error: super may be not be used on variable edits
         def edits: java.util.Vector[javax.swing.undo.UndoableEdit] = super.edits
                                                                            ^

Answer 1

嗯，总有反射(reflection)。

class Foo extends javax.swing.undo.UndoManager {
  def edits(): java.util.Vector[javax.swing.undo.UndoableEdit] =
    classOf[javax.swing.undo.CompoundEdit].
    getDeclaredField("edits").get(this).
    asInstanceOf[java.util.Vector[javax.swing.undo.UndoableEdit]]
}

你也可以通过嵌套来消除这两个调用的歧义，尽管这很丑陋:

class PreFoo extends javax.swing.undo.UndoManager {
  protected def editz = edits
}
class RealFoo extends PreFoo {
  def edits() = editz
}

您确实需要 ()，但它不会与字段本身冲突(并且您不能用 def< 覆盖 val/)。