“从内部类引用的局部变量必须是最终的或有效的最终变量”-如何解决？

Question

I've seen other threads with a similar issue, however in those threads the solution was to create a final variable with a copy of the values so that the variable is effectively final. However, my issue derives from the fact that the variable that produces the error is a 2D array holding instances of a class.

Here is code for the Controller class in which the error is happening:

package Controller;

import Model.Die;
import View.GameWindow;
import View.HelpWindow;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;

public class Controller {

private GameWindow view;
private static int pos[] = new int[2];
private Die diceLayout[][];
private String createdWord;

public Controller(){

    view = new GameWindow();
    addHelpListener();
    addSubmitListener();
    diceLayout = view.getDice();

}

private void submitWord(String word){
    boolean valid = checkValidWord(word);
    if(valid){
        System.out.println("The word ‘"+word+"‘ is valid.");
    }else{System.out.println("The word ‘"+word+"‘ is not valid.");}
}

private boolean checkValidWord(String word){
    boolean validSpell = validWordDic(word);
    boolean connected = checkWordConnected(word);
    if(validSpell&&connected){
        return true;
    }else{
        return false;
    }
}

private static boolean validWordDic(String word){
    word=word.toLowerCase();
    try {
        BufferedReader in = new BufferedReader(new FileReader("C:\\Users\\sambe\\Desktop\\IPT\\BoggleGame\\res\\dictionary.txt"));
        String str;
        while ((str = in.readLine()) != null) {
            if (str.indexOf(word) != -1) {
                return true;
            }
        }
        in.close();
    } catch (IOException e) {
        e.printStackTrace();
    }

    return false;
}

public boolean checkWordConnected(String word){
    word = word.toLowerCase();
    String letters[] = word.split("");
    for(int i = 0; i<4; i++){
        for(int j = 0; j<4; j++){
            if(letters[0]==diceLayout[i][j].getText()){
                pos[0]=i;
                pos[1]=j;
            }
        }
    }
    return true;
}

private void addHelpListener(){
    view.getHelpButton().addActionListener(new ActionListener(){
        @Override
        public void actionPerformed(ActionEvent e) { 
            HelpWindow helpWin = new HelpWindow();
            System.out.println("done");
        } 
    });
}

private void addSubmitListener(){
    view.getSubmitButton().addActionListener(new ActionListener(){
        @Override
        public void actionPerformed(ActionEvent e) {
            System.out.println("done");
            if(view.getSubmitField().getText()!=null){
                submitWord(view.getSubmitField().getText());
            }else{
                submitWord(createdWord);
                createdWord="";
            }
            view.getSubmitField().setText("");
        } 
    });
}

private void addDiceListeners(){
    for(int i = 0; i<4; i++){
        for(int j = 0; j<4; j++){
            diceLayout[i][j].addActionListener(new ActionListener(){
                @Override
                public void actionPerformed(ActionEvent e){
                    diceLayout[i][j].setClicked(true); //Error Occurs here
                }
            });
        }
    }
}
}

If anyone has any suggestions as to how I can fix this, it would be greatly appreciated. Thanks!

Answer 1

It is not about the array, it's about the loop counters. Since i and j are not effectively final (they are incremented by the loops), they cannot be used in the anonymous class.

diceLayout[i][j].setClicked(true);
           ^
       error here (and if you fixed that, it would appear at j)

You can extract the Die into a local variable and hence only access i and j outside the listener:

private void addDiceListeners()
{
    for (int i = 0; i < 4; i++)
    {
        for (int j = 0; j < 4; j++)
        {
            Die die = diceLayout[i][j];
            die.addActionListener(new ActionListener()
            {
                @Override
                public void actionPerformed(ActionEvent e)
                {
                    die.setClicked(true); 
                }
            });
        }
    }
}

Answer 2

Here:

diceLayout[i][j].setClicked(true); //Error Occurs here

Your problem are i and j. These are local variables from the enclosing method. And of course: those are loop counters, therefore you can't make them final.

This should do:

for(int i = 0; i<4; i++) {
    for(int j = 0; j<4; j++) {
      final int finalRow = i;
      final int finalColumn = j;

to then use the two final copies you just created instead of i and j. Or, you go as the other answer suggests and fetch the actual Die object to use (as final).