JLabel and AbstractButton's imageUpdate method should be better specified

Summary

Update the java doc for the imageUpdate method of JLabel and AbstractButton to better describe the handling of the image parameter.

Problem

The imageUpdate method for both JLabel and AbstractButton currently states that "if the current {@code Icon}'s image is not equal to the passed in image the method will return false".

This is not correct since Icons don't have an image, it would be an instance of ImageIcon that contains an image.

Nor is that sufficiently precise. In the case of JLabel if it is not showing then also this method return false. Similarly in the case of AbstractButton if the button for current button state is null then this method also returns false.

Solution

Update the documentation for these methods to be more accurate.

Specification

javax.swing.JLabel.imageUpdate(Image img, int infoflags, int x, int y, int w, int h) :

/**
-     * This is overridden to return false if the current Icon's Image is
-     * not equal to the passed in Image <code>img</code>.
+     * If the component is not showing or either the icon or disabled
+     * icon is not an {@code ImageIcon} with an  {@code Image}
+     * equal to the passed in {@code Image}, return {@code false};
+     * otherwise it will delegate to the super-class.

 public boolean imageUpdate(Image img, int infoflags, int x, int y, int w, int h)

javax.swing.AbstractButton.imageUpdate(Image img, int infoflags, int x, int y, int w, int h) :

/**
-     * This is overridden to return false if the current <code>Icon</code>'s
-     * <code>Image</code> is not equal to the
-     * passed in <code>Image</code> <code>img</code>.
+     * If the button icon for the current button state is either  {@code null}
+     * or not an {@code ImageIcon} with an {@code Image} equal to the
+     * passed in {@code Image}, return {@code false}; otherwise it
+     * will delegate to the super-class.

 public boolean imageUpdate(Image img, int infoflags, int x, int y, int w, int h)