Eclipse cannot compile some packages in rt. Jar

I have been writing someCodeIf some packages in rt. jar are referenced, for example:

Import
Sun. Misc. base64decoder 

Import
Com.sun.net. httpserver. headers;

The error message is:Access restriction: The type base64decoder is not accessible due
Restriction 
On required library D:/Java/JRE/lib/RT. Jar 

The solution is as follows: 
1. Open project properties. 
2. Select Java build path node. 
3. Select libraries tab. 
4. Remove JRE system library once 
5. Add library JRE system library again