Creating New Components In Swing

import javax.swing.*;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

/**
 * "Code early, Code often."
 */
public class SimpleFrame extends JFrame {

    int frameCount = 1;

    public SimpleFrame(){
        super("SimpleFrame");

        final JPanel centerPanel = new JPanel();//this panel will hold the new components we create.

        final JPanel topPanel = new JPanel();
        final String[] choices = new String[]{"Label", "Button", "Frame"};
        final JComboBox comboBox = new JComboBox(choices);
        final JButton addComponentButton = new JButton("Add");
        addComponentButton.addActionListener(new ActionListener(){
            public void actionPerformed(ActionEvent e) {
                //When the button addComponentButton is pressed, this code will execute.
                final Object selectedItem = comboBox.getSelectedItem();     // See what's selected in the combobox.
                if(null != selectedItem){
                    if("Label".equals(selectedItem)){
                        centerPanel.add(new JLabel("This is a label"));
                    }else if("Button".equals(selectedItem)){
                        centerPanel.add(new JButton("This is a Button"));
                    }else if("Frame".equals(selectedItem)){
                        JFrame newFrame = new JFrame("This is Frame#"+(frameCount));
                        frameCount++;
                        newFrame.setLocation(frameCount*20, frameCount*20);
                        newFrame.setSize(new Dimension(100,100));
                        newFrame.setVisible(true);
                    }else{
                        JOptionPane.showMessageDialog(null, "Button was pressed, but nothing was selected!");
                    }
                    topPanel.revalidate();
                }
            }
        });


        //add our combobox and button to the top panel
        topPanel.add(comboBox);
        topPanel.add(addComponentButton);


        //now we'll add our two panels to the frame's content pane, and we're done.
        getContentPane().setLayout(new BorderLayout());
        getContentPane().add(topPanel, BorderLayout.NORTH);
        getContentPane().add(centerPanel, BorderLayout.CENTER);

    }


    public static void main(String[] args) {
        SimpleFrame sf = new SimpleFrame();
        sf.setSize(new Dimension(800,600));
        sf.setVisible(true);
        sf.addWindowListener(new WindowAdapter() {
            @Override
            public void windowClosed(WindowEvent e) {
                System.exit(1);
            }
        });
    }

}