Bug 319509 [Viewers] Empty rows in CheckboxTableViewer with virtual table
bundles/org.eclipse.jface/src/org/eclipse/jface/viewers/CheckboxTableViewer.java
*
     * @param state <code>true</code> if the element should be checked,
     *  and <code>false</code> if it should be unchecked
     */
    public void setAllChecked(boolean state) {
        TableItem[] children = getTable().getItems();
        for (int i = 0; i < children.length; i++) {
            TableItem item = children[i];
            item.setChecked(state);
        }
    }
    /**
     * Sets to the given value the grayed state for all elements in this viewer.
     *
     * @param state <code>true</code> if the element should be grayed,
     *  and <code>false</code> if it should be ungrayed
     */
    public void setAllGrayed(boolean state) {
        TableItem[] children = getTable().getItems();
        for (int i = 0; i < children.length; i++) {
            TableItem item = children[i];
            item.setGrayed(state);
        }
    }
    /* (non-Javadoc)
     * Method declared on ICheckable.
     */
    public boolean setChecked(Object element, boolean state) {
        Assert.isNotNull(element);
        Widget widget = findItem(element);