java - 缩短一段代码会产生错误；我该如何解决这个问题？

Question

这个问题已经有答案了:

A final counter in a for loop? (6 个回答)

已关闭 8 年前。

我在一个方法中有这段代码:

switches[0].addMouseListener(new MouseAdapter(){
        public void mouseClicked(MouseEvent e)
        {
            if(switchstate[0] == false)
            {
                if((e.getX() >= OFFBUTTONLEFT && e.getX() <= OFFBUTTONRIGHT) && (e.getY() >= OFFBUTTONTOP && e.getY() <= OFFBUTTONDOWN))
                    switchstate[0] = true;
            }else
            {
                if((e.getX() >= ONBUTTONLEFT && e.getX() <= ONBUTTONRIGHT) && (e.getY() >= ONBUTTONTOP && e.getY() <= ONBUTTONDOWN))
                    switchstate[0] = false;
            }

            paintStuff();
        }
    });

switches[1].addMouseListener(new MouseAdapter(){
        public void mouseClicked(MouseEvent e)
        {
            if(switchstate[1] == false)
            {
                if((e.getX() >= OFFBUTTONLEFT && e.getX() <= OFFBUTTONRIGHT) && (e.getY() >= OFFBUTTONTOP && e.getY() <= OFFBUTTONDOWN))
                    switchstate[1] = true;
            }else
            {
                if((e.getX() >= ONBUTTONLEFT && e.getX() <= ONBUTTONRIGHT) && (e.getY() >= ONBUTTONTOP && e.getY() <= ONBUTTONDOWN))
                    switchstate[1] = false;
            }

            paintStuff();
        }
    });

switches[2].addMouseListener(new MouseAdapter(){
        public void mouseClicked(MouseEvent e)
        {
            if(switchstate[2] == false)
            {
                if((e.getX() >= OFFBUTTONLEFT && e.getX() <= OFFBUTTONRIGHT) && (e.getY() >= OFFBUTTONTOP && e.getY() <= OFFBUTTONDOWN))
                    switchstate[2] = true;
            }else
            {
                if((e.getX() >= ONBUTTONLEFT && e.getX() <= ONBUTTONRIGHT) && (e.getY() >= ONBUTTONTOP && e.getY() <= ONBUTTONDOWN))
                    switchstate[2] = false;
            }

            paintStuff();
        }
    });

变量(类的字段)在哪里

JLabel[] switches = new JLabel[3];      //I've initialized each index
boolean[] switchstate = new boolean[3]; //Indices Initialized to 'false'

和

final static int OFFBUTTONTOP   = 75;
final static int OFFBUTTONLEFT  = 30;
final static int OFFBUTTONRIGHT = 65;
final static int OFFBUTTONDOWN  = 115;

final static int ONBUTTONTOP   = 35;
final static int ONBUTTONLEFT  = 25;
final static int ONBUTTONRIGHT = 60;
final static int ONBUTTONDOWN  = 75;

我想缩短那段代码，所以我做到了

for(final int i=0; i<switchstate.length; i++)
    switches[i].addMouseListener(new MouseAdapter(){
        public void mouseClicked(MouseEvent e)
        {
            if(switchstate[i])
            {
                if(ON_RECTANGLE.contains(e.getX(), e.getY()))
                    switchstate[i] = false;
            }
            else
            {
                if(OFF_RECTANGLE.contains(e.getX(), e.getY()))
                    switchstate[i] = true;
            }
        }
    });

两个新变量是

final static Rectangle OFF_RECTANGLE = new Rectangle(30, 75, 35, 40); 
final static Rectangle ON_RECTANGLE  = new Rectangle(25, 35, 35, 30);

但是缩短的代码给了我一个错误:

error: local variable i is accessed from within inner class; needs to be declared final

但是如果我声明 i如final ，我无法使用i++正如它给出的那样

error: cannot assign a value to final variable i

如何避免这个问题？

Answer 1

使用另一个变量 -

for(int i = 0; i < switchstate.length; i++) {
    final int j = i;
    switches[i].addMouseListener(new MouseAdapter(){
        public void mouseClicked(MouseEvent e)
        {
            if(switchstate[j])
            {
                if(ON_RECTANGLE.contains(e.getX(), e.getY()))
                    switchstate[j] = false;
            }
            else
            {
                if(OFF_RECTANGLE.contains(e.getX(), e.getY()))
                    switchstate[j] = true;
            }

            paintStuff();
        }
    });
}

通过这种方式，您可以在 mouseClicked 方法中捕获 i 的值，而不是捕获变量本身(不幸的是 Java 还不允许)。