java - 不能引用非最终变量和计时器

Question

我正在尝试编写一个静态类，它可以更改控制背景，该控制背景将传递给参数。所以我实现了这个:

public static void wrong(final Component component) {

        component.setBackground(Color.RED);
        Timer   timer = new Timer(2, wrongAction);

        wrongAction = new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {

                int green = component.getBackground().getGreen();
                int blue = component.getBackground().getBlue();
                component.setBackground(new Color(255, green + 1, blue + 1));
                if (component.getBackground() == Color.WHITE) {
                    timer.stop();
                }
            }
        };

        timer.start();

    }  

我遇到了一个错误:

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

当然，我们可以将计时器更改为最终计时器，但这样做后方法将停止工作。
我尝试用 google 搜索并在其他 stackoverflow 主题中找到答案，但没有任何帮助。

提前非常感谢大家!

Answer 1

问题是您使用了不同的错误操作引用。

public static void wrong(final Component component) {

    component.setBackground(Color.RED);
    Timer   timer = new Timer(2, wrongAction);// <-- Here wrongAction is not the one you
                                              // define on the next line

    wrongAction = new ActionListener() { // <-- This is a new ActionListener but Timer
                                         // has no knowledge about it.
        @Override
        public void actionPerformed(ActionEvent e) {

            int green = component.getBackground().getGreen();
            int blue = component.getBackground().getBlue();
            component.setBackground(new Color(255, green + 1, blue + 1));
            if (component.getBackground() == Color.WHITE) {
                timer.stop();
            }
        }
    };

    timer.start();

}

下面的代码将立即运行(但我觉得不太干净，最好将所有这些封装在一个专用对象中，以便 Timer 可以成为类的变量并且监听器可以引用它) :

public static void wrong(final Component component) {
        class MyActionListener implements ActionListener {
            private Timer timer;

            public void setTimer(Timer timer) {
                this.timer = timer;
            }

            @Override
            public void actionPerformed(ActionEvent e) {

                int green = component.getBackground().getGreen();
                int blue = component.getBackground().getBlue();
                component.setBackground(new Color(255, green + 1, blue + 1));
                if (component.getBackground().equals(Color.WHITE)) {
                    if (timer == null) {
                        System.err.println("This sucks, I got no timer");
                    } else {
                        timer.stop();
                    }
                }

            }
        }
        MyActionListener wrongAction = new MyActionListener();
        component.setBackground(Color.RED);
        Timer timer = new Timer(2, wrongAction);
        wrongAction.setTimer(timer);


        timer.start();

    }