getting a JScrollPane to display its scrollbars

[chinomso ikwuagwu]

public Object [] showDeleteTableOptions() {
Vector listData = getListData();// This retrieves a vector containing the options
listData.trimToSize();
int size = listData.size();

JCheckBox [] checkBoxes = new JCheckBox[size];

JPanel panel = new JPanel();
panel.setLayout(new GridLayout(size, 1));

for (int i=0; i< size; i++) {
checkBoxes[i] = new JCheckBox(listData.get(i).toString());
panel.add(checkBoxes[i]);
}
int dialogResult = JOptionPane.showOptionDialog(this, new JScrollPane(panel), " Select table(s) to delete",
JOptionPane.DEFAULT_OPTION, JOptionPane.INFORMATION_MESSAGE, null, okAllCancel, okAllCancel[0]);

if (dialogResult ==0 ) {// Process...}
}

Question. Why doesn't the JScrollPane's scrollbar show when the panel contains a large list which is almost the height of the screen.

[marc weber]

Moving to Swing forum...

[Michael Dunn]

run this as is, then comment out the indicated line, and uncomment the block
run it again, then uncomment the preferredSize() line, and run it again

    
import javax.swing.*;
import java.awt.*;
class Testing extends JFrame
{
  JPanel p = new JPanel(new GridLayout(0,1));
  JScrollPane sp = new JScrollPane(p);
  public Testing()
  {
    setSize(600,400);
    setLocation(200,100);
    setDefaultCloseOperation(EXIT_ON_CLOSE);
    for(int x = 0; x < 50; x++)
    {
       p.add(new JLabel("Hello World"));
    }
    /*
    //sp.setPreferredSize(new Dimension(500,300));//test without this line, then with the line
    JPanel p1 = new JPanel();
    p1.add(sp);
    getContentPane().add(p1);
    */
    getContentPane().add(sp);//comment out this line, uncomment above block
  }
  public static void main(String[] args){new Testing().setVisible(true);}
}

[chinomso ikwuagwu]

Thanks! Learnt something new.