Java Code:
import org.eclipse.swt.SWT;
import org.eclipse.swt.layout.FormAttachment;
import org.eclipse.swt.layout.FormData;
import org.eclipse.swt.layout.FormLayout;
import org.eclipse.swt.widgets.Button;
import org.eclipse.swt.widgets.Display;
import org.eclipse.swt.widgets.Shell;

public class FormLayoutSample {

  Display display = new Display();
  Shell shell = new Shell(display);

  public FormLayoutSample() {

    shell.setLayout(new FormLayout());
    Button button1 = new Button(shell, SWT.PUSH);
    button1.setText("button1");

    FormData formData = new FormData();
    formData.left = new FormAttachment(20);
    formData.top = new FormAttachment(20);
    button1.setLayoutData(formData);    
    Button button2 = new Button(shell, SWT.PUSH);
    button2.setText("button number 2");
    formData = new FormData();
    formData.left = new FormAttachment(button1, 0, SWT.CENTER);
    formData.top = new FormAttachment(button1, 0, SWT.CENTER);
    button2.setLayoutData(formData);
//    Button button3 = new Button(shell, SWT.PUSH);
//    button3.setText("3");
//    
//    formData = new FormData();
//    formData.top = new FormAttachment(button2, 10);
//    formData.left = new FormAttachment(button2, 0, SWT.LEFT);
//    button3.setLayoutData(formData);

    shell.pack();
    //shell.setSize(500, 600);
    shell.open();
    //textUser.forceFocus();
    //System.out.println("Button3: " + button3.getBounds());

    // Set up the event loop.
    while (!shell.isDisposed()) {
      if (!display.readAndDispatch()) {
        // If no more entries in event queue
        display.sleep();
      }
    }

    display.dispose();
  }

  private void init() {

  }

  public static void main(String[] args) {
    new FormLayoutSample();
  }
}