有没有办法可以将其放入for循环中？

Question

I updated the code to use for loops, and an arrayList for the buttons. now it has given me an error.

java.lang.NullPointerException

BlueJ editor is pointing to this line.

for(int i=0; i<=buttonsList.size(); i++){

I think it has something to do with instance variables not existing or something before the arrayList. Also, it compiles perfectly, but when I run main, it then goes back to the line in the code!

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.util.ArrayList;

//Created class the extends JFrame, and implements action listener
public class Board extends JFrame implements ActionListener 
{
//Instance variables 
private JButton b1, b2, b3, b4, b5, b6, b7, b8, b9, reset;
private ArrayList<JButton> buttonsList;

//'playerO' uses the letter 'O', not the number zero
Icon playerO = new ImageIcon("images/playerO.jpg");
Icon playerX = new ImageIcon("images/playerX.jpg");
Icon playerN = new ImageIcon("images/reset.jpg");

//Instance variable to determine player turn
boolean firstPlayer = true;

//Constructor
public Board()
{
    //Title of Frame
    super("Gui7 - TicTacToe || Jose Reyes");

    //Created container and set the layout
    Container c = getContentPane();
    c.setLayout(new BorderLayout());

    //Created a panel, and set the layout
    JPanel gridPanel = new JPanel();
    gridPanel.setLayout(new GridLayout(3,3));

    //Created new JButtons and added them to the array list 
    for(int i=0; i<=buttonsList.size(); i++){
        JButton jBut = new JButton(playerN);
        buttonsList.add(jBut);
    }

    //Created reset button and title
    reset = new JButton("Play Again?");

    //Added buttons to panel with for loop
    for(int i=0; i<=buttonsList.size(); i++){
        gridPanel.add(buttonsList.get(i));
    }

    //Added panel and reset button to container
    c.add(gridPanel);
    c.add(reset, BorderLayout.PAGE_END);

    //Added Action Listeners with loop
    for(int i=0; i<=buttonsList.size(); i++){
        buttonsList.get(i).addActionListener(this);
    }

    //Added action listener to reset button
    reset.addActionListener(this);

    //Set the window size and set visibility
    setSize(600,600);
    setVisible(true);
}

//ActionEvents
public void actionPerformed(ActionEvent e)
{
    //Grab source
    Object src = e.getSource();

    for (int i = 0; i<=buttonsList.size(); i++){
        if(src == buttonsList.get(i)){
            if(firstPlayer){
                buttonsList.get(i).setIcon(playerO);
                firstPlayer = false;
            } else {
                buttonsList.get(i).setIcon(playerX);
                firstPlayer = true;
            }
        }
    }


    //Reset button icons with loop
    if(src == reset){
        for (int i = 0; i < 9; i++){
            buttonsList.get(i).setIcon(playerN);
        }

        firstPlayer = true;
    }

}

//Main method
public static void main (String args[])
{
    Board t = new Board();
    t.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
}

Answer 1

Rather than have a bunch of variables named b1 ... b9 , make an array of whatever type b1 is. Then you can iterate over the array like this:

for (int i = 0; i < 9; i++){
    if(src == bArray[i]){
       if(firstPlayer){
          bArray[i].setIcon(playerO);
          firstPlayer = false;
       } else {
          bArray[i].setIcon(playerX);
          firstPlayer = true;
       }
    }
}

Answer 2

Yes you can do this with a for loop.

First, store all your buttons in an array or arraylist. Since the other answer is an array, I'll do arraylist.

ArrayList<Button> buttonsList = new ArrayList<>();
buttonsList.add(b1);
buttonsList.add(b2);

etc. Then,

for (Button b: buttonsList){
    if (src == b) {
        if (firstPlayer) {
            b.setIcon(playerO);
            firstPlayer = false;
        } else {
            b.setIcon(playerX);
            firstPlayer = true;
        }
    }
}

EDIT: I suggest you just use an arraylist instead of array. Its much easier to work with since you don't need to specify a size before hand.

Instead of this line:

private JButton buttons[];

Do

private ArrayList<Button> buttonList = new Arraylist()<>;

Additionally change,

for(int i=0; i<10; i++){
        buttons[i] = new JButton(playerN);
}
//do this instead
for(int i=0; i<10; i++){
    JButton jBut = new JButton(playerN);
    buttonsList.add(jBut);
}

//Added buttons to panel with for loop
for(int i=0; i<10; i++){
    gridPanel.add(buttons[i]);
}
//Do this instead
//Added buttons to panel with for loop
for(int i=0; i<10; i++){
    gridPanel.add(buttonsList.get(i));
}

EDIT2: This is almost definitely causing one of your problems lol

//Added Action Listeners with loop
for(int i=0; i<10; i++){
    buttons[1].addActionListener(this);
}

You are adding the listener to the second button- buttons[1] every time. Change that to buttons[i].addActionListener(this); and it will probably work.

Answer 3

something like below should work.

JButton[] buttons = new JButton[9]; // i'll leave you to fill it

for(int i = 0; i < buttons.length; i++){ // assuming the array is filled
 if(src == buttons[i]){
   if(firstPlayer){
      buttons[i].setIcon(playerO);
      firstPlayer = false;
   } else {
      buttons[i].setIcon(playerX);
      firstPlayer = true;
   }
 }
}