SWT Jface Eclipse Java

//Send questions, comments, bug reports, etc. to the authors:
//Rob Warner (rwarner@interspatial.com)
//Robert Harris (rbrt_harris@yahoo.com)
import org.eclipse.swt.events.*;
import org.eclipse.swt.widgets.*;
import org.eclipse.swt.custom.StackLayout;
import org.eclipse.swt.SWT;
public class StackLayoutTest {
  public static void main(String[] args) {
    Display display = new Display();
    Shell shell = new Shell(display);
    StackLayout layout = new StackLayout();
    shell.setLayout(layout);
    StackLayoutSelectionAdapter adapter = new StackLayoutSelectionAdapter(shell,
        layout);
    Button one = new Button(shell, SWT.PUSH);
    one.setText("one");
    one.addSelectionListener(adapter);
    Button two = new Button(shell, SWT.PUSH);
    two.setText("two");
    two.addSelectionListener(adapter);
    Button three = new Button(shell, SWT.PUSH);
    three.setText("three");
    three.addSelectionListener(adapter);
    layout.topControl = one;
    shell.open();
    while (!shell.isDisposed()) {
      if (!display.readAndDispatch()) {
        display.sleep();
      }
    }
    display.dispose();
  }
}
class StackLayoutSelectionAdapter extends SelectionAdapter {
  Shell shell;
  StackLayout layout;
  public StackLayoutSelectionAdapter(Shell shell, StackLayout layout) {
    this.shell = shell;
    this.layout = layout;
  }
  public void widgetSelected(SelectionEvent event) {
    Control control = layout.topControl;
    Control[] children = shell.getChildren();
    int i = 0;
    for (int n = children.length; i < n; i++) {
      Control child = children[i];
      if (child == control) {
        break;
      }
    }
    ++i;
    if (i >= children.length) {
      i = 0;
    }
    layout.topControl = children[i];
    shell.layout();
  }
}