8263472: Specification of JComponent::updateUI should document that t…

…he default implementation does nothing

Reviewed-by: aivanov, darcy

src/java.desktop/share/classes/javax/swing/JComponent.java

@@ -656,15 +656,18 @@ public JComponent() {
 
 
     /**
-     * Resets the UI property to a value from the current look and feel.
-     * <code>JComponent</code> subclasses must override this method
+     * This method is called to update the UI property to a value from the
+     * current look and feel.
+     * {@code JComponent} subclasses must override this method
      * like this:
      * <pre>
      *   public void updateUI() {
      *      setUI((SliderUI)UIManager.getUI(this);
      *   }
      *  </pre>
      *
+     * @implSpec The default implementation of this method does nothing.
+     *
      * @see #setUI
      * @see UIManager#getLookAndFeel
      * @see UIManager#getUI