Performing Builds Automatically
  To indicate that you want the Workbench to perform incremental builds whenever resources are saved:
  
    - Open the 
     General > Workspace
    preference page. General > Workspace
    preference page.
- Select the Build automatically checkbox.
- Click OK to close the Preferences page. The Workbench will automatically perform incremental builds of
    resources modified since the last build. Whenever a resource is modified, another incremental build occurs.
Builds
  Performing builds manually
  Changing build order