Option Explicit

Private Declare Function SetWindowLong Lib "user32" Alias "SetWindowLongA" (ByVal hwnd As Long, ByVal nIndex As Long, ByVal dwNewLong As Long) As Long

Private Sub Form_KeyDown(KeyCode As Integer, Shift As Integer)
    Static fHeight As Single
    Static fWidth  As Single
    Static fLeft   As Single
    Static fTop    As Single
    Static fStyle  As Long
    If (KeyCode = vbKeyReturn) And (Shift And vbAltMask) Then
        If fStyle Then
            SetWindowLong hwnd, -16&, fStyle
            WindowState = vbNormal
            Height = fHeight
            Width = fWidth
            Left = fLeft
            Top = fTop
            fStyle = 0
        Else
            fTop = Top
            fLeft = Left
            fWidth = Width
            fHeight = Height
            fStyle = SetWindowLong(hwnd, -16&, &H16000000)
            WindowState = vbMaximized
        End If
    End If
End Sub

import java.awt.Dimension;
import java.awt.Event;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.KeyStroke;
public class FullScreen extends JPanel implements ActionListener {
    private static final long        serialVersionUID    = -4312447806272150211L;
    private static final Dimension    DEFAULT_SIZE        = new Dimension(300, 300);
    private boolean                    isFullScreen        = false; // pas super elegant mais  bon
    private JFrame                    parent                = null;
    public FullScreen(JFrame parent) {
        super();
        this.parent = parent;// pour les changements de taille
        registerKeyboardAction(this, KeyStroke.getKeyStroke(KeyEvent.VK_ENTER,
                Event.ALT_MASK), JComponent.WHEN_IN_FOCUSED_WINDOW);
    }
    /**
     * pout le test
     */
    public static void main(String[] args) {
        JFrame f = new JFrame("Test Ctrl+Enter");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.setSize(DEFAULT_SIZE);
        f.setLocationRelativeTo(null);
        f.setContentPane(new FullScreen(f));
        f.setVisible(true);
    }
    public void actionPerformed(ActionEvent e) {
        if (e.getSource().equals(this)) {// pour le cas ou il y ai d'autres  composants
            if (!isFullScreen) {
                parent.setSize(getToolkit().getScreenSize());
                parent.setLocation(0, 0);// pour eviter les decalages
                isFullScreen = true;
            } else {
                parent.setSize(DEFAULT_SIZE);
                parent.setLocationRelativeTo(null);// pour eviter les decalages
                isFullScreen = false;
            }
        }
    }
}

Maximise()