java - final 局部变量无法赋值，因为它是在封闭类型中定义的

Question

ratingS = new JSlider(1, 5, 3); 
ratingS.setMajorTickSpacing(1);
ratingS.setPaintLabels(true);
int vote;

class SliderMoved implements ChangeListener {
    public void stateChanged(ChangeEvent e) {
        vote = ratingS.getValue();
    }
}

ratingS.addChangeListener(new SliderMoved());

如果我写上面的代码，Eclipse 会告诉我:

Cannot refer to a non-final variable vote inside an inner class defined in a different method

但是如果我在 int vote 之前添加 final 它会给我这个错误:

The final local variable vote cannot be assigned, since it is defined in an enclosing type

那么，如何解决呢？

Answer 1

嗯，标准技巧是使用长度为 1 的 int 数组。使 var 最终并写入 var[0]。确保不造成数据竞争非常重要。以您的代码为例:

final int[] vote = {0};

class SliderMoved implements ChangeListener {
  public void stateChanged(ChangeEvent e) {
    vote[0] = ratingS.getValue();
  }
}

由于所有这些都将在 EDT 上发生，包括回调调用，您应该是安全的。您还应该考虑使用匿名类:

ratingS.addChangeListener(new ChangeListener() {
  public void stateChanged(ChangeEvent e) { vote[0] = ratingS.getValue(); }
});