我想在Java中单击组合框名称时更改组合框颜色

Question

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class combodemo implements ActionListener {
    JFrame f;
    JPanel p;
    JTextField tf;
    JButton b1;
    JButton b2;
    JRadioButton rb1;
    JRadioButton rb2;
    JLabel l;
    JComboBox cb;
    JCheckBox c1, c2, c3;
    ButtonGroup bg;

    combodemo() {
        String[] h = {
            "red",
            "yellow",
            "green"
        };
        cb = new JComboBox(h);
        f = new JFrame();
        p = new JPanel();
        tf = new JTextField(30);
        b1 = new JButton("OK");
        b2 = new JButton("Clear");
        rb1 = new JRadioButton("male");
        rb2 = new JRadioButton("Female");
        l = new JLabel("Enter Text");
        c1 = new JCheckBox("java");
        c2 = new JCheckBox("C++");
        c3 = new JCheckBox("Microsoft");
        bg = new ButtonGroup();

        f.add(p);
        p.add(l);
        p.add(tf);
        b1.addActionListener(this);
        b2.addActionListener(this);
        p.add(b1);
        p.add(b2);
        bg.add(rb1);
        bg.add(rb2);
        p.add(rb1);
        p.add(rb2);
        p.add(cb);
        p.add(c1);
        p.add(c2);
        p.add(c3);

        f.setVisible(true);
        f.pack();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    }
    public void actionPerformed(ActionEvent ae)

    {
        String str = (String) cb.getSelectedItem();
        '
        if (str.equals("red"))
            p.setBackground(Color.red);

        if (str.equals("green"))
            p.setBackground(Color.green);

        if (str.equals("yellow"))
            p.setBackground(Color.yellow);

        if (ae.getActionCommand() == "OK") {
            tf.setText("This is example of swing");
        }
        if (ae.getActionCommand() == "Clear") {
            tf.setText("");
        }
    }
    public static void main(String[] args)

    {
        combodemo cd = new combodemo();
    }
}

Actually when I run this code and to change the color of panel when I click on "RED", "GREEN" or "YELLOW", it requires me to click on "OK" in order to change the color of panel. I want to change the color while clicking on the name on "RED", "GREEN" or "Yellow" please help me to get rid of this problem.

I learn this code from NIIT in today's lecture and when I coded it then many errors has occurred. But now I have completed the code but the problem I'm facing now I already written above.

Help will be appreciated.

Answer 1

You need to do two things..

first add actionlistner to jcombobox

cb.addActionListener(this);

second, implement logic for handling the event.

public void actionPerformed(ActionEvent ae)

{
    if(ae.getSource() instanceof JComboBox) {
            String str = (String)cb.getSelectedItem();
            if(str.equals("red"))
            p.setBackground(Color.red);

            if(str.equals("green"))
            p.setBackground(Color.green);

            if(str.equals("yellow"))
            p.setBackground(Color.yellow);
        }
          /////

Complete code

package test;
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class combodemo implements ActionListener
{
JFrame f;
JPanel p;
JTextField tf;
JButton b1;
JButton b2;
JRadioButton rb1;
JRadioButton rb2;
JLabel l;
JComboBox cb;
JCheckBox c1,c2,c3;
ButtonGroup bg;

combodemo()
{
String  []h = {"red","yellow","green"};
cb = new JComboBox(h);
f = new JFrame();
p = new JPanel();
tf = new JTextField(30);
b1 = new JButton("OK");
b2 = new JButton("Clear");
rb1 = new JRadioButton("male");
rb2 = new JRadioButton("Female");
l = new JLabel("Enter Text");
c1 = new JCheckBox("java");
c2 = new JCheckBox("C++");
c3 = new JCheckBox("Microsoft");
bg = new ButtonGroup();

f.add(p);
p.add(l);
p.add(tf);
b1.addActionListener(this);
b2.addActionListener(this);
cb.addActionListener(this);
p.add(b1);
p.add(b2);
bg.add(rb1);
bg.add(rb2);
p.add(rb1);
p.add(rb2);
p.add(cb);
p.add(c1);
p.add(c2);
p.add(c3);

f.setVisible(true);
f.pack();
f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
}
public void actionPerformed(ActionEvent ae)

{
    if(ae.getSource() instanceof JComboBox) {
        String str = (String)cb.getSelectedItem();
        if(str.equals("red"))
        p.setBackground(Color.red);

        if(str.equals("green"))
        p.setBackground(Color.green);

        if(str.equals("yellow"))
        p.setBackground(Color.yellow);
    }


if(ae.getActionCommand()=="OK")
{
tf.setText("This is example of swing");
}
if(ae.getActionCommand()=="Clear")
{
tf.setText("");
}
}
public static void main (String [] args)

{
combodemo cd = new combodemo();
} 
}