ECalc is a calculator plug-in for Eclipse that provides the ability to evaluate mathematical expressions. Note the low version number. At this stage the software should be considered a prototype, although it does work pretty well.
To install, just put the jar from the zip-files in your plugin-directory and restart eclipse. To uninstall, remove the jar-file and the directory .metadata/.plugin/se.fnord.ecalc from your workspace directory/directories.
Click on this link to get more detail: http://ecalc.fnord.se/
Recommend the tutorial