Java Local variable mi defined in an enclosing scope must be final or effectively final

Question

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 lt 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

User · Answer

Yes this is happening because you are accessing mi variable from within your anonymous inner class  what happens deep inside is that another copy of your variable is created and will be use inside the anonymous inner class  so for data consistency the compiler will try  restrict you from changing the value of mi so that s why its telling you to set it to final

User · Answer

As I can see the array is of String only For each loop can be used to get individual element of the array and put them in local inner class for use   Below is the code snippet for it           WorkAround      for  String color   colors     String pos   Character toUpperCase color charAt 0     color substring 1   JMenuItem Jmi  new JMenuItem pos   Jmi setIcon new IconA color     Jmi addActionListener new ActionListener              Override         public void actionPerformed ActionEvent e                JMenuItem item    JMenuItem  e getSource                IconA icon    IconA  item getIcon                   HERE YOU USE THE String color variable and no errors                Color kolorIkony   getColour color                textArea setForeground kolorIkony                          mnForeground add Jmi

User · Answer

What you have here is a non-local variable  https   en wikipedia org wiki Non-local variable   i e  you access a local variable in a method an anonymous class   Local variables of the method are kept on the stack and lost as soon as the method ends  however even after the method ends  the local inner class object is still alive on the heap and will need to access this variable  here  when an action is performed    I would suggest two workarounds   Either you make your own class that implements actionlistenner and takes as constructor argument  your variable and keeps it as an class attribute  Therefore you would only access this variable within the same object   Or  and this is probably the best solution  just qualify a copy of the variable final to access it in the inner scope as the error suggests to make it a constant   This would suit your case since you are not modifying the value of the variable

User · Answer

The error means you cannot use the local variable mi inside an inner class      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     So your code will be like this   for  int mi 0  mi lt 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

User · Answer

One solution is to create a named class instead of using an anonymous class  Give that named class a constructor that takes whatever parameters you wish and assigns them to class fields   class MenuActionListener implements ActionListener       private Color kolorIkony       public MenuActionListener Color kolorIkony            this kolorIkony   kolorIkony             Override     public void actionPerformed ActionEvent e            JMenuItem item    JMenuItem  e getSource            IconA icon    IconA  item getIcon               Use the class field here         textArea setForeground kolorIkony               Now you can create an instance of this class as usual   Jmi addActionListener new MenuActionListener getColor colors mi

[java] Java: Local variable mi defined in an enclosing scope must be final or effectively final

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