无法分配最终的局部变量，因为它是在封闭类型中定义的 [英] The final local variable cannot be assigned, since it is defined in an enclosing type

问题描述

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告诉我：

If i write the above code Eclipse tells me this:

不能引用以不同方法定义的内部类
内的非最终变量投票

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

但如果我在 int vote 之前添加最终，则会出现此错误：

But if i add final before int vote it gives me this error:

无法分配最终的局部变量投票，因为它是在封闭类型中定义的

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

那么，如何解决？

推荐答案

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

Well, the standard trick is to use an int array of length one. Make the var final and write to var[0]. It is very important to make sure you don't create a data race. Using your code as an example:

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，你应该是安全的。您还应该考虑使用匿名类：

Since all this will be happenenig on the EDT, including the callback invocation, you should be safe. You should also consider using the anonymous class:

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

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