使用swing，JButtons等在程序上显示信息的问题

Question

I'm making a multiplication table using swing.Its basically made up of JButtons. The table is formed from input from the user. The user selects the size of the table by entering a number. The last thing i need to do with this is create a heading that displays the numbers of the table created. Here is my sample code, if you run it, you'll see that its done for the vertical numbers. How can i get the numbers above and properly formatted to represent each column. Thank you.

package lab7;

import java.awt.BorderLayout;
import java.awt.GridBagLayout;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

public class GUIMultiplicationTable{
JFrame theFrame;
int number = 0;
JPanel panel, answerPanel, topPanel, leftPanel;
JLabel answerLabel, topLabel, leftLabel;

private void createAndShowGui(){
    String x;
    do{
        x = JOptionPane.showInputDialog(null, "Enter the number");
        number = Integer.parseInt(x);
    }while (number <= 0);
    theFrame = new JFrame("Multiplication Table");
    panel = new JPanel(new GridLayout(number, number));

    answerPanel = new JPanel();     
    answerLabel = new JLabel();

    topPanel = new JPanel();
    topLabel = new JLabel();

    leftPanel = new JPanel();
    leftLabel = new JLabel();


    for (int i = 0; i < number; i++){
        JLabel blah = new JLabel(Integer.toString(i + 1));
        panel.add(blah);//add center to label
        for (int j = 0; j < number; j++){

            JButton button = new JButton();
            if (i == 0){

                button.setText(String.valueOf(j + 1));
            }
            if (j == 0){
                button.setText(String.valueOf(i + 1));
            }
            for (int k = 1; k < number; k++)
            {
                if (i == k)
                {
                    button.setText(String.valueOf((j + 1) * (k + 1)));
                }
            }
            button.addActionListener(new ButtonsTableActionListener(i, j));
            panel.add(button);
        }   
    }

    answerPanel.add(answerLabel);
    theFrame.add(answerPanel, BorderLayout.SOUTH);

    topPanel.add(topLabel);
    theFrame.add(topPanel, BorderLayout.NORTH);

    theFrame.add(panel);
    theFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    theFrame.pack();
    theFrame.setLocationRelativeTo(null);
    theFrame.setVisible(true);
}
public static void main(String[] args){
    SwingUtilities.invokeLater(new Runnable(){
        public void run(){
            GUIMultiplicationTable h = new GUIMultiplicationTable();
            h.createAndShowGui();
        }
    });
}

private class ButtonsTableActionListener implements ActionListener{
    private int theRow, theColumn;

    public ButtonsTableActionListener(int row, int column){
        theRow = row;
        theColumn = column;
    }

    @Override
    public void actionPerformed(ActionEvent e){
        int value = (theRow + 1) * (theColumn + 1);
        answerLabel.setText("The value is: " + value + ".\nI got that by multiplying \n" +    (theRow + 1) + "x" + (theColumn + 1));
    }
};
}

Answer 1

The loop in your actionListener is not required, the source of the event is the button that triggered it, so you can simply do...

JButton source = (JButton) e.getSource();
JOptionPane.showMessageDialog(theFrame, source.getText());

Instead.

Now having said that, I would, personally, use some kind of Map to link the JButton to the value, removing the need to have to try and cast the text of the button back to a numeric value (which I believe would be your next step), or store other information you might need to work with for the button (such as the values required to produce the answer)...

private Map<JButton, int[]> answers = new HashMap<JButton, int[]>(25);
//...

for(int i = 0; i < number; i++){
    for(int j = 0; j < number; j++){
        buttons[i][j] = new JButton();
        if(i ==  0) {
            buttons[i][j].setText(String.valueOf(j+1));
        }
        if(j == 0) {
            buttons[i][j].setText(String.valueOf(i+1));
        }
        for(int k = 1; k < number; k++){
            if(i == k){
                buttons[i][j].setText(String.valueOf((j+1) * (k+1)));
            }
        }
        panel.add(buttons[i][j]);
        // Store the answer here...
        answers.put(buttons[i][j], new int[]{i, j});
    }
}

//...

public void actionPerformed(ActionEvent evt) {
    JButton source = (JButton) e.getSource();
    int[] answer = answers.get(source);
    JPanel panel = new JPanel();
    JTextField[] fields = new JTextField[]{
        new JTextField(2),
        new JTextField(2)
    };
    panel.add(fields[0]);
    panel.add(new JLabel("x"));
    panel.add(fields[1]);
    panel.add(new JLabel(" = " + source.getText()));
    JOptionPane.showMessageDialog(theFrame, panel);
    // check the values of the fields against the
    // values of the answer
}

Answer 2

Everything you need to do is just putting a JLabel somewhere.

final JLabel resultLabel = new JLabel("Select a button!");

Note that it should be final to be able to use it in the ActionListener . In the ActionListener you already had the right way, just look at these few lines to make it happen:

ActionListener first = new ActionListener(){
    @Override
    public void actionPerformed(ActionEvent e) {
         for(int i = 0; i < number; i++){
                for(int j = 0; j < number; j++){
                    if(buttons[i][j] == e.getSource()){

                       // write the equation to the label
                        resultLabel.setText(buttons[i][j].getText() 
                                          + " = " + (i+1) + " * " 
                                          + (j+1));
                       // since you found the button you can now break
                        break;
                    }
                }
         }
    }
};

Note the i+1 and j+1 . The buttons are indexed from 0 to number-1, so the button at (0,0) actually shows the result of 1*1.

This is also important for your next two lines of code:

// you used i=1 and j=1, but you have to start with 0 to make it work for all buttons
for(int i = 0; i < number; i++){
    for(int j = 0; j < number; j++){
        buttons[i][j].addActionListener(first);
    }
}

At a last step you also have to show the the label. If you just add it to the frame, as you do with the panel, you will see that you will not see it.

theFrame.add(resultLabel);
theFrame.add(panel);

The problem is that theFrame doesn't have a layoutmanager yet. So use a new Layout here as well:

theFrame.setLayout(new GridLayout(2,1));

Of course there will be better choices or some nice tweeks to make the layout more beautiful.

So as in sum how to change your code from top to bottom:

• set a Layout for theFrame
• create a new JLabel for the result of the click, make it final
• set the label's text in the actionPerformed() method
• add the label to theFrame

You can also consider putting the Label into a new JPanel and add that Panel to theFrame.

Answer 3

An easy way to do this is to store the position of the button in the ActionListener , you can accomplish this by making your own class extending ActionListener , instead of doing an anonymous class. This way the code executed by the button will already have the information it needs to accomplish whatever you want.

Also you don't need the array of buttons, just add a button in the panel at a time, and at the same time add the actionListener.

This is your code cleaned up and working properly. Now, instead of showing a dialog do whatever you want to do.

import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

public class GUIMultiplicationTable
{
    JFrame theFrame;
    int number = 0;
    JPanel panel;

    private void createAndShowGui()
    {
        String x;
        do
        {
            x = JOptionPane.showInputDialog(null, "Enter the number");
            number = Integer.parseInt(x);
        } while (number <= 0);
        theFrame = new JFrame("Multiplication Table");
        panel = new JPanel(new GridLayout(number, number));
        for (int i = 0; i < number; i++)
        {
            for (int j = 0; j < number; j++)
            {
                JButton button = new JButton();
                if (i == 0)
                {
                    button.setText(String.valueOf(j + 1));
                }
                if (j == 0)
                {
                    button.setText(String.valueOf(i + 1));
                }
                for (int k = 1; k < number; k++)
                {
                    if (i == k)
                    {
                        button.setText(String.valueOf((j + 1) * (k + 1)));
                    }
                }
                button.addActionListener(new ButtonsTableActionListener(i, j));
                panel.add(button);
            }
        }
        theFrame.add(panel);
        theFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        theFrame.pack();
        theFrame.setLocationRelativeTo(null);
        theFrame.setVisible(true);

    }

    public static void main(String[] args)
    {
        SwingUtilities.invokeLater(new Runnable() {
            public void run()
            {
                GUIMultiplicationTable h = new GUIMultiplicationTable();
                h.createAndShowGui();
            }
        });

    }

    private class ButtonsTableActionListener implements ActionListener
    {
        private int _row, _column;

        public ButtonsTableActionListener(int row, int column)
        {
            _row = row;
            _column = column;
        }

        @Override
        public void actionPerformed(ActionEvent e)
        {
            // /do something
            int value = (_row + 1) * (_column + 1);
            String message = "I'm the button in the position (" + _row + ", " + _column + ")\nMy value is " + value + " = " + (_row + 1) + "*" + (_column + 1);
            JOptionPane.showMessageDialog(theFrame, message);
        }
    };
}