public abstract class AbstractSpreedsheetEditorPart extends EditorPart {

@Override
public void createPartControl(Composite parent) {
    initializeTableViewer(parent);
    populateTable(this);
    if (tableDecorator != null) {
        tableDecorator.decorate(this)
    }
}
}


public class MarkedItemTableDecorator implements TableDecoratorInterface  {
    editorPart AbstractSpreedsheetEditorPart;

    public decorate(AbstractSpreedsheetEditorPart part){
        editorPart = part;
        addKeysListeners(); // this works
        addButtons();       // this does not
    }

    private void addKeysListeners() {
    editorPart.getTable().addKeyListener(new KeyListener() {

        @Override
        public void keyReleased(KeyEvent e) {
            // TODO Auto-generated method stub
        }

        @Override
        public void keyPressed(KeyEvent e) {
            switch (e.keyCode) {
                case SWT.INSERT: onInsert();
                break;
            }
        }
    });
}

private void addButtons() {
    Composite canvas = editorPart.getCanvas();
    Button button = new Button(canvas, SWT.PUSH);
    button.setLayoutData(new GridData(SWT.LEFT, SWT.BOTTOM, false, false, 1, 1));
    button.setText("Insert");
    button.setToolTipText("Shortcut: [insert]");
    button.addMouseListener(new MouseListener() {

        @Override
        public void mouseUp(MouseEvent e) {
            onInsert();
        }

        @Override
        public void mouseDown(MouseEvent e) {
            // TODO Auto-generated method stub
        }

        @Override
        public void mouseDoubleClick(MouseEvent e) {
            // TODO Auto-generated method stub
        }
    });
}