摇摆Java ActionListener

Question

I have been trying to show a message on the Frame saying that "Car is selected " After the I press the button OK ; i have been trying to fix this problem buti dont know how to can anyone please help me ?

import java.awt.Container;
import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;
import java.util.HashMap;
import java.util.Map;
import javax.swing.JButton;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JLabel;

public class SelectWindow extends JFrame implements ItemListener {

    public static void main(String[] args) {
        new SelectWindow();
    }
    Map<String, String[]> cars = new HashMap<String, String[]>();
    JComboBox brands;
    JComboBox models;

    public SelectWindow() {
        initCars();
        setTitle("Select a car");
        brands = new JComboBox();
        brands.addItem("<none>");
        for (String brand : cars.keySet()) {
            brands.addItem(brand);
        }
        brands.addItemListener(this);
        models = new JComboBox();
        models.setEnabled(false);
        models.addItemListener(this);
        Container c = getContentPane();
        c.setLayout(new FlowLayout());
        c.add(new JLabel("Select a brand: "));
        c.add(brands);
        c.add(new JLabel("Select a model: "));
        c.add(models);
        c.add(new JButton("OK"));
        setVisible(true);
    }

    @Override
    public void itemStateChanged(ItemEvent e) {
        if (e.getSource() == brands && e.getStateChange() == ItemEvent.SELECTED) {
            String[] items = cars.get(e.getItem());
            if (items == null) {
                models.removeAllItems();
                models.setEnabled(false);
            } else {
                models.removeAllItems();
                models.addItem("<none>");
                for (String item : items) {
                    models.addItem(item);
                }
                models.setEnabled(true);
            }
            JLabel texte = new JLabel("car was selected");
            JButton.addActionListener(new ActionListener() {
                public void actionPerformed(ActionEvent arg0) {
                    texte.setVisible(true);
                }
            });
        }
    }

    private void initCars() {
        cars.put("Renault", new String[]{
            "Twingo", "Clio", "Modus", "Kangoo",
            "Mégane", "Sénic", "Laguna", "Expace"});
        cars.put("Peugeot", new String[]{
            "107", "206", "207", "308", "407",
            "508", "607"});
        cars.put("Citroën", new String[]{
            "C1", "C3", "C4 Picasso", "C5", "C6", "C8",
            "Berlingo", "DS3"});
    }
}

Answer 1

Start by taking a look at How to Use Buttons, Check Boxes, and Radio Buttons and How to Write an Action Listener

Buttons provide notification via ActionListener s. You need to register an instance of ActionListener with your button and perform your required actions within it

On a slightly more advance topic, but a worth while read How to Use Actions which provides a self contained ActionListener which also carries the configuration information which can be used by buttons, including menu items, and key bindings

This...

JLabel texte = new JLabel("car was selected");
JButton.addActionListener(new ActionListener() {
    public void actionPerformed(ActionEvent arg0) {
        texte.setVisible(true);
    }
});

Isn't going to work for two reasons;

1. JButton does not provide a static method addActionListener , so this won't compile...
2. texte hasn't been added to anything, so trying to make it visible won't work...

Personally, I would initialise this in along with the rest of UI...

JLabel texte = new JLabel("car was selected");
JButton btn = new JButton("OK");
btn.addActionListener(new ActionListener() {
    public void actionPerformed(ActionEvent arg0) {
        texte.setVisible(true);
    }
});
c.add(btn);
c.add(texte);

Now, you could use your itemStateChanged method to enabled/disable the button, but you would need to make btn an instance variable...

public class SelectWindow extends JFrame implements ItemListener {
    //...
    private JButton okBtn;
    //...
    public SelectWindow() {
        //...
        okBtn = new JButton("OK");
        okBtn.addActionListener(new ActionListener() {
            //...
        });
        c.add(okBtn);
        //...

This would allow you to change the state of the button in the itemStateChanged

public void itemStateChanged(ItemEvent e) {
    //...
    okBtn.setEnabled(...);

For example...

...Side notes and comments...

• Generally, it's discouraged to extend from top level containers, like JFrame and instead use a more common level container like JPanel . This increases the re-usability of you UI, as you're not locking yourself into a single top level container and you can decided when and how your component show be used, for example...

Answer 2

There is no response on the button because you did not have a reference on it you just add to the Frame without having a reference on it;

problem:

c.add(new JButton("OK")); //wont have any reference

solution

 button = new JButton("OK")
 c.add(button );

where button is a global variable .

and in your itemStateChanged method changed the

JButton.addActionListener(new ActionListener() {
                public void actionPerformed(ActionEvent arg0) {
                }
            });

to

button.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent arg0) {
            }
        });

To register your global reference of button's actionListener

Answer 3

I've modified your code and it works now

 import java.awt.Container;
 import java.awt.FlowLayout;
 import java.awt.event.ActionEvent;
 import java.awt.event.ActionListener;
 import java.awt.event.ItemEvent;
 import java.awt.event.ItemListener;
 import java.util.HashMap;
 import java.util.Map;
 import javax.swing.JButton;
 import javax.swing.JComboBox;
 import javax.swing.JFrame;
 import javax.swing.JLabel;
 public class SelectWindow extends JFrame implements
 ItemListener {
     JButton button1;
     JLabel texte;
      Container c;
 public static void main(String[] args) {
 new SelectWindow();
 }

 Map<String, String[]> cars = new HashMap<String,
 String[]>();
 JComboBox brands;
 JComboBox models;
 public SelectWindow() {
 initCars();
 setTitle("Select a car");
 brands = new JComboBox();
 brands.addItem("<none>");
 for (String brand : cars.keySet()) {
 brands.addItem(brand);
 }
 brands.addItemListener(this);
 models = new JComboBox();
 models.setEnabled(false);
 models.addItemListener(this);
 texte = new JLabel("car was selected");
 texte.setVisible(false);
 button1 = new JButton("OK");

 button1.addActionListener(new ActionListener() {

     public void actionPerformed(ActionEvent arg0) {

         texte.setVisible(true);
        // c.add(texte);
     }
        });

 c = getContentPane();
 c.setLayout(new FlowLayout());
 c.add(new JLabel("Select a brand: "));
 c.add(brands);
 c.add(new JLabel("Select a model: "));
 c.add(models);
 c.add(button1);
 c.add(texte);
 setVisible(true);
 }
 @Override
 public void itemStateChanged(ItemEvent e) {
 if (e.getSource() == brands && e.getStateChange() == ItemEvent.SELECTED) {
   String[] items = cars.get(e.getItem());
 if (items == null) {
    models.removeAllItems();
     models.setEnabled(false);

 } else {
     models.removeAllItems();
     models.addItem("<none>");
 for (String item : items) {
     models.addItem(item);
 }
      models.setEnabled(true);

 }

 button1.setEnabled(true);



     }



 }
private void initCars() {
   cars.put("Renault", new String[] {
   "Twingo", "Clio", "Modus", "Kangoo",
     "Mégane", "Sénic", "Laguna", "Expace" });
cars.put("Peugeot", new String[] {
 "107", "206", "207", "308", "407",
 "508", "607" });
 cars.put("Citroën", new String[] {
 "C1", "C3", "C4 Picasso", "C5", "C6", "C8",
     "Berlingo", "DS3" });
   }
 }

Let me know if this was what you were looking for! Just changed the buttons and container and text to Global variables. Set the label visibility to False initially and added it to the container and later set it to True when Button clicked.