SWT Jface Eclipse Java

import org.eclipse.swt.SWT;
import org.eclipse.swt.layout.*;
import org.eclipse.swt.events.*;
import org.eclipse.swt.graphics.Image;
import org.eclipse.swt.widgets.*;
public class TreeShellExample {    
        Display d;
        Shell s;
        TreeShellExample()    {
            d = new Display();
            s = new Shell(d);
            
            s.setSize(250,200);
            
            s.setText("A Table Shell Example");
            s.setLayout(new FillLayout());
            Tree t = new Tree(s, SWT.SINGLE | SWT.BORDER);
            TreeItem child1 = new TreeItem(t, SWT.NONE, 0);
            child1.setText("1");
            TreeItem child2 = new TreeItem(t, SWT.NONE, 1);
            child2.setText("2");
            TreeItem child2a = new TreeItem(child2, SWT.NONE, 0);
            child2a.setText("2A");
            TreeItem child2b = new TreeItem(child2, SWT.NONE, 1);
            child2b.setText("2B");
            TreeItem child3 = new TreeItem(t, SWT.NONE, 2);
            child3.setText("3");
            s.open();
            while(!s.isDisposed()){
                if(!d.readAndDispatch())
                    d.sleep();
            }
            d.dispose();
        }
        public static void main(String[] argv){
          new TreeShellExample();
        }
}