JDT Core 

JDT Core (org.eclipse.jdt.core) is the plug-in that defines the core Java elements and API. You should always list this plug-in as a prerequisite when you are developing Java specific features.

JDT Core packages give you access to the Java model objects and headless Java IDE infrastructure.  The JDT Core packages include:

Manipulation of the structure of a compilation unit should be done using org.eclipse.jdt.core.dom instead of org.eclipse.jdt.core.jdom. org.eclipse.jdt.core.jdom will be deprecated in the 2.2. stream and replaced with org.eclipse.jdt.core.dom.

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