مشكلة في الـ JComboBox

فقط أضف الشرط if (e.getStateChange() == ItemEvent.SELECTED)

import java.awt.Dimension;
import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;
import java.io.IOException;


import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;

public class JComboBoxTest extends JFrame implements ItemListener {

	private String[] numbers = {"Choose number to display", "10", "100", "1000"};
	private JComboBox chart = new JComboBox(numbers);

	public static void main(String[] args) throws IOException {

		JComboBoxTest frame = new JComboBoxTest();
		frame.setSize(250, 100);
		frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		frame.setVisible(true);
	}

	public JComboBoxTest() {
		JPanel p = new JPanel();
		p.add(chart);
		chart.setSelectedIndex(0);
		chart.setPreferredSize(new Dimension(200, 40));

		// add combo box to the frame
		getContentPane().add(p);

		// Register listeners
		chart.addItemListener(this);
	}

	public void itemStateChanged(ItemEvent e) {
		if (e.getStateChange() == ItemEvent.SELECTED) {
			String ItemSelectd = (String) e.getItem();

			if (e.getSource() instanceof JComboBox) {
				if ("10".equals(ItemSelectd)) {
					JOptionPane.showMessageDialog(null, "the number is ten",
									null, JOptionPane.INFORMATION_MESSAGE);
				}

				if ("100".equals(ItemSelectd)) {
					JOptionPane.showMessageDialog(null, "the number is hundred",
									null, JOptionPane.INFORMATION_MESSAGE);
				}

				if ("1000".equals(ItemSelectd)) {
					JOptionPane.showMessageDialog(null, "the number is thousend",
									null, JOptionPane.INFORMATION_MESSAGE);
				}
			}
		}
	}
}

ودا حل اخر باستخدم الـ ActionListener

تفضل

import java.awt.Dimension;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.IOException;
import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;

public class JComboBoxTest extends JFrame implements ActionListener {

	private String[] numbers = {"Choose number to display", "10", "100", "1000"};
	private JComboBox chart = new JComboBox(numbers);

	public static void main(String[] args) throws IOException {

    	JComboBoxTest frame = new JComboBoxTest();
    	frame.setSize(250, 100);
    	frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    	frame.setLocationRelativeTo(null);
    	frame.setVisible(true);
	}

	public JComboBoxTest() {
    	JPanel p = new JPanel();
    	p.add(chart);
    	chart.setSelectedIndex(0);
    	chart.setPreferredSize(new Dimension(200, 40));

    	// add combo box to the frame
    	getContentPane().add(p);

    	// Register listeners
    	chart.addActionListener(this);
	}

	@Override
	public void actionPerformed(ActionEvent e) {
    	String item = (String) chart.getSelectedItem();
    	if (numbers[1].equals(item)) {
        	JOptionPane.showMessageDialog(null, "the number is ten",
                	null, JOptionPane.INFORMATION_MESSAGE);
    	} else if (numbers[2].equals(item)) {
        	JOptionPane.showMessageDialog(null, "the number is hundred",
                	null, JOptionPane.INFORMATION_MESSAGE);
    	} else if (numbers[3].equals(item)) {
        	JOptionPane.showMessageDialog(null, "the number is thousend",
                	null, JOptionPane.INFORMATION_MESSAGE);
    	}
	}
}

أو قم باستخدام ActionListener، وكل ما عليك تغييره هو:

chart.addActionListener(this);

public void actionPerformed(ActionEvent e)
    {
        if(((String) ((JComboBox) e.getSource()).getSelectedItem()).equals("10"))
        { 
            JOptionPane.showMessageDialog(null, "the number is ten", null,JOptionPane.INFORMATION_MESSAGE); 
        } 
        else if(((String) ((JComboBox) e.getSource()).getSelectedItem()).equals("100"))
        { 
            JOptionPane.showMessageDialog(null, "the number is hundred", null,JOptionPane.INFORMATION_MESSAGE); 
        } 
        else if(((String) ((JComboBox) e.getSource()).getSelectedItem()).equals("1000"))
        { 
            JOptionPane.showMessageDialog(null, "the number is thousend", null,JOptionPane.INFORMATION_MESSAGE); 
        }
    }