在JButton OnclickListener中编辑JLabel文本

Question

I am fairly new to programming, and I have recently begun messing with the JFrame in java. I am creating a program where the user can scroll through a pokedex using two buttons. I have two JLabels, showing the pokedex number, and the pokedex name. I have hit a roadblock, not able to change the jlabel text, based on strings and ints, which are edited within the onclick listener. Please tell me what I am doing wrong.

package window;

import java.awt.BorderLayout;
import java.awt.Canvas;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;

import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingConstants;

import javax.imageio.ImageIO;
import javax.swing.Icon;
import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFrame;

public class RunWindow extends Canvas implements Runnable{

    private static final long serialVersionUID = 1L;

    public static final int WIDTH = 800;
    public static final int HEIGHT = 600;
    public static final int SCALE = 1;
    public static final String NAME = "Pokedex";
    public int pokedexNum = 1;
    public String pokedexName = "Bulbasaur";
    private JFrame frame;
    private JPanel panel = new JPanel();
    private JButton b1;
    private JButton b2;
    private boolean update = true;

    JLabel label;
    JLabel label2;
    public boolean running = false;

    public RunWindow(){
        BufferedImage imgUP = null;
        do {
            switch(pokedexNum){
                case 1:
                    pokedexName = "Bulbasaur";
                    break;
                case 2:
                    pokedexName = "Ivysaur";
                    break;
                case 3:
                    pokedexName = "Venisaur";
                    break;

            }
            label = new JLabel("Pokemon #"+pokedexNum+"-"+pokedexName);
            label2 = new JLabel("#"+pokedexNum);
            update = false;
        }while (update);

        label = new JLabel("Pokemon #"+pokedexNum+"-"+pokedexName);
        label2 = new JLabel("#"+pokedexNum);

        label.setLocation(50, 50);
        frame = new JFrame(NAME);
        b1 = new JButton("Up");
        b2 = new JButton("Down");
        frame.setMinimumSize(new Dimension(WIDTH * SCALE, HEIGHT * SCALE));
        frame.setPreferredSize(new Dimension(WIDTH*SCALE,HEIGHT*SCALE));
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setLayout(new BorderLayout());
        frame.add(this,BorderLayout.CENTER);
        frame.setResizable(false);
        frame.add(label);
        frame.add(label2);
        frame.add(panel);
        frame.add(b1);
        frame.add(b2);
        frame.pack();
        frame.setVisible(true);
        frame.setLocationRelativeTo(null);

        b1.setBounds(300, 400, 40, 20);
        b1.addActionListener(new ActionListener() { 
                public void actionPerformed(ActionEvent e) { 

                System.out.println(pokedexNum);
                if(pokedexNum <= 3){
                pokedexNum++;
                switch(pokedexNum){
                case 1:
                pokedexName = "Bulbasaur";
                break;
                case 2:
                pokedexName = "Ivysaur";
                break;
                case 3:
                pokedexName = "Venisaur";
                break;

                }
                label = new JLabel("Pokemon #"+pokedexNum+"-"+pokedexName);
                label2 = new JLabel("#"+pokedexNum);
                update = false;
                System.out.println(pokedexName);
                label.setText("Pokemon #"+pokedexNum+"-"+pokedexName);
                label2.setText("#"+pokedexNum);
                label.setText(label.getText());

                }
                }

        } );
        b2.addActionListener(new ActionListener() { 
                public void actionPerformed(ActionEvent e) {
                pokedexNum--;
                System.out.println("Down");
                }
                } );
        b2.setBounds(300, 420, 40, 20);
        b1.setHorizontalTextPosition(JButton.CENTER);
        b1.setVerticalTextPosition(JButton.CENTER);
        label.setBounds(300, 50, 200, 24); 
        label2.setBounds(340,400,80,20);
        frame.add( label, BorderLayout.NORTH );
        frame.add( panel , BorderLayout.CENTER);

    }
    public void run() {

    }
    public synchronized void start(){
        running = true;
        new Thread(this).start();

    }
    public void updatePokedex(){
        do {
            switch(pokedexNum){
                case 1:
                    pokedexName = "Bulbasaur";
                    break;
                case 2:
                    pokedexName = "Ivysaur";
                    break;
                case 3:
                    pokedexName = "Venisaur";
                    break;

            }
            label = new JLabel("Pokemon #"+pokedexNum+"-"+pokedexName);
            label2 = new JLabel("#"+pokedexNum);
            update = false;
        }while (update);
    }
    public synchronized void stop(){
        running = false;
    }
    public static void main(String[] args){
        new RunWindow().start();
    }

}

Answer 1

I did not look at your code in full detail, but from what I've seen, you seem to be creating JLabels a lot, and this can be the cause of the problem, because the labels you have initially created are the ones which you added to your Swing components, and which are being displayed inside the JFrame.

You should reuse these labels and simply use their setText methods, to change the text they are displaying.

Answer 2

You already have 2 Label variables and you only want to change the text, but you create new labels everytime:

label = new JLabel("Pokemon #"+pokedexNum+"-"+pokedexName);

instead you should just do:

label.setText("....");

As you do some lines later anyways. The problem is that you never add the newly created labels to the frame (you add them at the start, but when you override "label" and "label2" those are NEW labels and you'd need to also add them to your frame, resulting in 2 labels added everytime you click a button)

Just remove:

    label = new JLabel("Pokemon #"+pokedexNum+"-"+pokedexName);
    label2 = new JLabel("#"+pokedexNum);

I would also advise you to not use switch statements, you should rather use a string array and just call

setText(pokemonNames[pokedexNum]);

This way you don't need hundreds of codelines for different pokedex cases.

You can create a String[] easily like this way:

private static String[] pokeNames = new String[]{"","Bulbasaur","Ivysaur"};

I included an empty String at the start so that the index of the array is the same as the number in the pokedex (index starts at 1 so to say).