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

Hi everyone, here is the code:

Code:

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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

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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.

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,

Code:

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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);
  }
}

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Thanks for the quick and very clear answer.

Quote:

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Originally Posted by fatabass

Thanks for the quick and very clear answer.

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You are quite welcome!

Moved from 'New to Java'

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