Why can't I add both a JList and a JScrollPane to my JFrame?

**fatabass** · 12-27-2011, 10:24 PM

Hi everyone, here is the code:

Java Code:

public class ListFrame extends JFrame
{
	JList myJList;
	String[] colorrs;
	
	public ListFrame()
	{
		super("This is a List Frame");
		this.setLayout(new FlowLayout());
		
		colorrs = new String[6];
		colorrs[0] = "Red";
		colorrs[1] = "Blue";
		colorrs[2] = "Green";
		colorrs[3] = "Black";
		colorrs[4] = "White";
		colorrs[5] = "Purple";
		
		myJList = new JList();
		myJList.setListData(colorrs);
		myJList.setVisibleRowCount(4);
		
		JScrollPane scrollPane = new JScrollPane(myJList);
		this.add(scrollPane);
		
		
		//this.add(myJList);
		
		
	}// end Constructor
}//end Class

With this code, I get a nice JScrollPane that includes myJList with the options.

But:
If I remove the comment slashes from last statement I have(//this.add(myJList);), I am expecting to see both the JScrollPane and myJList.

However I only get an ugly JList with no scrolling option. JScrollPane gets invisible.

Any help?

Thanks.

**Fubarable** · 12-27-2011, 10:27 PM

A component can only be added once to a visible GUI. If you try to add it twice, the last component only is seen. To remedy the situation, use two JLists that share the same model.

For example,

Java Code:

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

public class ListFrame extends JFrame
{
    JList myJList;
    String[] colorrs;
     
    public ListFrame()
    {
        super("This is a List Frame");
        this.setLayout(new FlowLayout());
         
        colorrs = new String[6];
        colorrs[0] = "Red";
        colorrs[1] = "Blue";
        colorrs[2] = "Green";
        colorrs[3] = "Black";
        colorrs[4] = "White";
        colorrs[5] = "Purple";
         
        myJList = new JList();
        myJList.setListData(colorrs);
        myJList.setVisibleRowCount(4);
         
        JScrollPane scrollPane = new JScrollPane(myJList);
        this.add(scrollPane);
         
         JList newList = new JList(myJList.getModel());
        this.add(newList);
         
         
    }
    
    public static void main(String[] args) {
      ListFrame listFrame = new ListFrame();
      listFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      listFrame.pack();
      listFrame.setLocationRelativeTo(null);
      listFrame.setVisible(true);
   }
}