If you have many projects in a workspace but only work on a few at a time, you might want to explore the Working Sets feature to control the visibility of projects. You can configure one or more working sets and quickly switch between them.
To do this, click the downward-pointing triangle in the toolbar of the COBOL Explorer, and click Select Working Set. Click New, select Resource as the Working set type and specify which projects and files should be part of it.
Once you have created a working set, it appears on the menu displayed by clicking the downward-pointing triangle in the toolbar of the COBOL Explorer view, as does Deselect Working Set (which takes you back to the default view of the workspace).
When you are have enabled a working set, Eclipse performs a full build of the projects that are part of that working set or have a file that is part of the working set.