Java Code:
import org.eclipse.swt.SWT;
import org.eclipse.swt.events.*;
import org.eclipse.swt.graphics.*;
import org.eclipse.swt.layout.*;
import org.eclipse.swt.widgets.*;

/**
 * This class demonstrates a Canvas
 */
public class SimpleCanvas {
  /**
   * Runs the application
   */
  public void run() {
    Display display = new Display();
    Shell shell = new Shell(display);
    shell.setText("Canvas Example");
    createContents(shell);
    shell.open();
    while (!shell.isDisposed()) {
      if (!display.readAndDispatch()) {
        display.sleep();
      }
    }
    display.dispose();
  }

  /**
   * Creates the main window's contents
   * 
   * @param shell the main window
   */
  private void createContents(Shell shell) {
    shell.setLayout(new FillLayout());

    // Create a canvas
    Canvas canvas = new Canvas(shell, SWT.NONE);

    // Create a button on the canvas
    Button button = new Button(canvas, SWT.PUSH);
    button.setBounds(10, 10, 300, 40);
    button.setText("You can place widgets on a canvas");

    // Create a paint handler for the canvas
    canvas.addPaintListener(new PaintListener() {
      public void paintControl(PaintEvent e) {
        // Do some drawing
        Rectangle rect = ((Canvas) e.widget).getBounds();
        e.gc.setForeground(e.display.getSystemColor(SWT.COLOR_RED));
        e.gc.drawFocus(5, 5, rect.width - 10, rect.height - 10);
        e.gc.drawText("You can draw text directly on a canvas", 60, 60);
      }
    });
  }

  /**
   * The application entry point
   * 
   * @param args the command line arguments
   */
  public static void main(String[] args) {
    new SimpleCanvas().run();
  }
}