Eclipse and Restrict Access to rt.jar

Edit project properties.
Under the "Libraries Tab" select the "JRE System Libary" > to expand.

Then click to select the "Acces rules:" item and click the "Edit" button.

Add a rule, by selecting the "Add Button"

Enter the rule pattern.  For example, I am trying to use sun.misc.BASE64Encoder.  Therefore, I add the rule pattern "sun/misc/**"

The Eclipse Editor should no long complain about accessing the sun.misc.BASE64Encoder.