Java：在封闭范围内定义的局部变量mi必须是最终的或有效的最终 [英] Java: Local variable mi defined in an enclosing scope must be final or effectively final

问题描述

我得到了错误，就像在主题中一样，我恳请你如何修复它...
ERROR在menuItem-loop中，我尝试将textArea前景色设置为从menuItem中选择的颜色： （colors [mi]）

I get the error, as in subject, and I kindly ask you how to repair it... ERROR is in menuItem-loop, where I try to set the textArea foreground colour to one picked from menuItem: (colors[mi])

    String[] colors = {
            "blue", 
            "yellow",
            "orange",
            "red", 
            "white", 
            "black", 
            "green", 
            };

JMenu mnForeground = new JMenu("Foreground");
            for (int mi=0; mi<colors.length; mi++){
                String pos = Character.toUpperCase(colors[mi].charAt(0)) + colors[mi].substring(1);
                JMenuItem Jmi =new JMenuItem(pos);
                Jmi.setIcon(new IconA(colors[mi]));

                Jmi.addActionListener(new ActionListener() {
                    @Override
                    public void actionPerformed(ActionEvent e) {
                        JMenuItem item = (JMenuItem) e.getSource();
                        IconA icon = (IconA) item.getIcon();
                        Color kolorIkony = getColour(colors[mi]); // ERROR HERE: (colors[mi])
                        textArea.setForeground(kolorIkony);
                    }
                });

                mnForeground.add(Jmi);
            }

public Color getColour(String colour){
  try {
      kolor = Color.decode(colour);
  } catch (Exception e) {
      kolor = null; 
  }
  try {
        final Field f = Color.class.getField(colour);
        kolor = (Color) f.get(null);
      } catch (Exception ce) {
        kolor = Color.black;
      }
return kolor;
}

推荐答案

错误表示你不能在内部类中使用局部变量 mi 。

The error means you cannot use the local variable mi inside an inner class.

要在内部类中使用变量，必须声明它 final 。只要 mi 是循环的计数器并且 final 变量无法分配，您必须创建一个变通方法来获取 mi 可以在内部类中访问的 final 变量中的值：

To use a variable inside an inner class you must declare it final. As long as mi is the counter of the loop and final variables cannot be assigned, you must create a workaround to get mi value in a final variable that can be accessed inside inner class:

final Integer innerMi = new Integer(mi);

所以你的代码是这样的：

So your code will be like this:

for (int mi=0; mi<colors.length; mi++){

    String pos = Character.toUpperCase(colors[mi].charAt(0)) + colors[mi].substring(1);
    JMenuItem Jmi =new JMenuItem(pos);
    Jmi.setIcon(new IconA(colors[mi]));

    // workaround:
    final Integer innerMi = new Integer(mi);

    Jmi.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                JMenuItem item = (JMenuItem) e.getSource();
                IconA icon = (IconA) item.getIcon();
                // HERE YOU USE THE FINAL innerMi variable and no errors!!!
                Color kolorIkony = getColour(colors[innerMi]); 
                textArea.setForeground(kolorIkony);
            }
        });

        mnForeground.add(Jmi);
    }
}

这篇关于Java：在封闭范围内定义的局部变量mi必须是最终的或有效的最终的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！