使用 GUI（Java）递增/递减

Question

I am supposed to implement an application to the user that has 2 buttons(Increment/decrement) and a label. When increment is pressed the number increases and decreases by one when decrement is pressed. The number starts at 50. I have it to where it shows the buttons and they work, but they work on 2 different variables, so their is 2 number printed to the screen instead of 1. My question is how can i make the button act on only one number. I have seen people use push etc. but is there another way to do this by passing in a value to both or something? Thanks

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

public class ButtonModifier 
{
    public static void main(String[] args)
    {
        JFrame frame = new JFrame();

        FlowLayout flow = new FlowLayout();
        frame.getContentPane().setLayout(flow);

        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(400,300);
        frame.setTitle("Button Modifier");

        IncrementPanel panel = new IncrementPanel();
        DecrementPanel panel1 = new DecrementPanel();

        frame.add(panel);
        frame.add(panel1);

        frame.setVisible(true);
    }
}

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

public class DecrementPanel extends JPanel
{
    private JButton button1;
    private JLabel label;
    private int number = 50;

    public DecrementPanel()
    {
        button1 = new JButton("Decrement");
        button1.addActionListener(new /*DecrementPanel.*/ButtonListener());

        label = new JLabel("" + number);


        this.add(button1);
        this.add(label);
    }

    private class ButtonListener implements ActionListener
    {
        public void actionPerformed(ActionEvent event)
        {
            //int increment = 50;

            number--;

            label.setText("" + number);


        }
    }

}

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

public class IncrementPanel extends JPanel
{
    private JButton button;
    private JLabel label;
    int number = 50;

    public IncrementPanel()
    {
        button = new JButton("Increment");
        button.addActionListener(new ButtonListener());

        label = new JLabel("" + number);

        this.add(button);
        this.add(label);
    }

    private class ButtonListener implements ActionListener
    {
        public void actionPerformed(ActionEvent event)
        {
            //int increment = 50;

            number++;

            label.setText("" + number);
        }
    }

}

Answer 1

I am supposed to implement an application to the user that has 2 buttons(Increment/decrement) and a label."

Then why do you have two?

 IncrementPanel panel = new IncrementPanel();
 DecrementPanel panel1 = new DecrementPanel();

Just use one and change the text on that one

Should be more like this

public class ButtonModifier extends JFrame {
    private JLabel numberLabel = new JLable("50");
    private JButton decrease = new JButton("-1");
    private JButton increase = new JButton("+1");
    private static int num = 50;

    public ButtonModifier(){
        setLayout(new GridLayout(1, 3));
        add(increase);
        add(numberLabel);
        add(decrease);

        increase.addActionListener(new ActionListener(){
            public void actionPerformed(ActionEvent e){
                num++;
                numLabel.setText("" + num);               
            }
        });
        decrease.addActionListener(new ActionListener(){
            public void actionPerformed(ActionEvent e){
                num--;
                numLabel.setText("" + num);               
            }
        }); 
    }

    public static void main(String[] args){
        JFrame frame = ButtonModifier();

        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(400,300);
        frame.setTitle("Button Modifier");
        frame.setVisible(true);
    }
}

Answer 2

You should have one JLabel which will display the only number in your program.

Then your two buttons will do operations on that number and update the label.

Your mistake is that each Panel has its own number and its own Label to display the number.

public class ButtonModifier {
    private static int number = 50;
    private static JLabel label;

    public static void main(String[] args) {
        JFrame frame = new JFrame();

        label = new JLabel("" + number);

        // <SNIP>

        JButton increment = new JButton("Increment");
        increment.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent event) {
                number++;
                label.setText("" + number);
            }
        }

        JButton decrement = new JButton("Increment");
        increment.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent event) {
                number--;
                label.setText("" + number);
            }
        }

        frame.add(label);
        frame.add(increment);
        frame.add(decrement);

        frame.setVisible(true);
    }
}

---

An important note: Swing is not thread-safe , and all the operations with GUI components must be performed on Event Dispatch Thread . So your main must actually look this way:

public static void main(String[] args) {
    SwingUtilities.invokeLater(new Runnable() {
        public void run() {
            // Here you create the frame and all the components
        }
    });
}

Answer 3

Create the JLabel in the main function. Have the incrementPanel and DecrementPanel classes constructors take a JLabel as an argument that they store as a private variable. The ButtonListeners csn also be passed the JLabel as an argument. Now the button listeners csn update a common JLabel. Now, you can improve things by combining the code of IncrementPanel and DecrementPanel classes by passing an int in the constructor indicating the increment of +1 or -1. A quick and dirty way to implement the functionality is through the use of anonymous classes implementing button listeners within a single monolithic class.

Answer 4

Take a look at this program :

import java.awt.BorderLayout;
import java.awt.FlowLayout;
import java.awt.Font;
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.JPanel;

public class IncDecApp extends JFrame {

    private JButton incBtn = new JButton("Increment");
    private JButton decBtn = new JButton("Decrement");
    private JPanel lowPanel = new JPanel(new FlowLayout(FlowLayout.CENTER));
    private JLabel showLbl = new JLabel("00", JLabel.CENTER);
    private Font myFont = new Font("Tahoma", Font.BOLD, 60);

    private int valueInt;

    public IncDecApp() {

        setTitle("IncDec Application =)");
        setDefaultCloseOperation(EXIT_ON_CLOSE);

        lowPanel.add(incBtn);
        lowPanel.add(decBtn);

        incBtn.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                valueInt = Integer.parseInt(showLbl.getText());
                valueInt++;
                if (valueInt >= 10) {
                    showLbl.setText(String.valueOf(valueInt));
                } else {
                    showLbl.setText("0" + String.valueOf(valueInt));
                }
            }
        });

        decBtn.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent e) {
                valueInt = Integer.parseInt(showLbl.getText());
                if (valueInt > 0) {
                    valueInt--;
                }
                if (valueInt >= 10) {
                    showLbl.setText(String.valueOf(valueInt));
                } else {
                    showLbl.setText("0" + String.valueOf(valueInt));
                }
            }
        });

        showLbl.setFont(myFont);

        add(showLbl, BorderLayout.CENTER);
        add(lowPanel, BorderLayout.SOUTH);
        pack();
        setLocationRelativeTo(null);
        setVisible(true);

    }

    public static void main(String[] args) {
        new IncDecApp();
    }

}

Answer 5

import java.awt.*;
import java.awt.event.*;
import java.applet.*;

public class ButtonApplet extends Applet implements ActionListener{

    Button buttonInc, buttonDec;
    int x=0;

    public void init(){

        buttonInc=new Button("Increment");
        buttonDec=new Button("Decrement");
        buttonInc.addActionListener(this);
        buttonDec.addActionListener(this);

        add(buttonInc);
        add(buttonDec);
    }

    public void paint(Graphics g){

        g.drawString("Count is : "+x,50,100);
    }

    public void actionPerformed(ActionEvent ev){

            if(ev.getSource() == buttonInc)
            {
                x++;
                repaint();
            }
            else if(ev.getSource() == buttonDec){
                x--;
                repaint();
            }
        }
}

Answer 6

Make Java GUI Application using AWT

You are required to make one label (Count), one textfield, one button (Increment), one button (Decrement) and one button (Close)

When the increment button is clicked, you need to increment the value in textfield, value should be incremented again and again when the button is clicked

When the decrement button is clicked, you need to decrement the value in textfield, value should be decremented again and again when the button is clicked

When the close button is clicked, you need to close the AWT Frame