The following elements (methods and variables) of class javax.swing.plaf.metal.MetalToolTipUI are present in JavaDoc but lack any specification except signature:

protected boolean isAcceleratorHidden()
public String getAcceleratorString()
public static ComponentUI createUI(JComponent c)
public MetalToolTipUI()
public static final int padSpaceBetweenStrings

Please note that 4 of 5 elements are PUBLIC.