Erro na aplicacao

<blockquote><div class="quote-author">dapim:</div>import java.awt.Toolkit;

import java.awt.Dimension;

import java.awt.GridBagLayout;

import java.awt.GridBagConstraints;

import javax.swing.JFrame;

import javax.swing.JButton;

import javax.swing.BorderFactory;

import javax.swing.border.Border;

public class TryGridBagLayout {

// The window object

static JFrame aWindow = new JFrame(?This is a Gridbag Layout?);

public static void main(String[] args) {

Toolkit theKit = aWindow.getToolkit(); // Get the window toolkit

Dimension wndSize = theKit.getScreenSize(); // Get screen size

// Set the position to screen center & size to half screen size

aWindow.setBounds(wndSize.width/4, wndSize.height/4, // Position

wndSize.width/2, wndSize.height/2); // Size

aWindow.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

GridBagLayout gridbag = new GridBagLayout(); // Create a layout manager

GridBagConstraints constraints = new GridBagConstraints();

aWindow.getContentPane().setLayout(gridbag); // Set the container layout mgr

// Set constraints and add first button

constraints.weightx = constraints.weighty = 10.0;

constraints.fill = constraints.BOTH; // Fill the space

addButton(? Press ?, constraints, gridbag); // Add the button

// Set constraints and add second button

constraints.gridwidth = constraints.REMAINDER; // Rest of the row

addButton(?GO?, constraints, gridbag); // Create and add button

aWindow.setVisible(true); // Display the window

}

static void addButton(String label,

GridBagConstraints constraints,

GridBagLayout layout) {

// Create a Border object using a BorderFactory method

Border edge = BorderFactory.createRaisedBevelBorder();

JButton button = new JButton(label); // Create a button

button.setBorder(edge); // Add its border

layout.setConstraints(button, constraints); // Set the constraints

aWindow.getContentPane().add(button); // Add button to content pane

}

}