Bug 4240 Can't edit class path entry (1GKEPIF)
There is no way to edit an existing entry for a library on the Java Build Path project properties page (other than editing the .classpath file directly). NOTES: EG (9/22/2001 11:42:11 AM) this is particularly annoying for variables. we should have an Edit button when a variable is selected.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/wizards/buildpaths/LibrariesWorkbookPage.java
public IPath getSourceAttachmentPath() {
			return fSourceAttachmentBlock.getSourceAttachmentPath();
		}
		
		public IPath getSourceAttachmentRootPath() {
			return fSourceAttachmentBlock.getSourceAttachmentRootPath();
		}
				
	}
	
	/*
	 * @see BuildPathBasePage#getSelection
	 */
	public List getSelection() {
		return fLibrariesList.getSelectedElements();
	}
	/*
	 * @see BuildPathBasePage#setSelection
	 */	
	public void setSelection(List selElements) {
		for (int i= selElements.size()-1; i >= 0; i--) {
			CPListElement curr= (CPListElement) selElements.get(i);
			if (!isLibraryKind(curr.getEntryKind())) {
				selElements.remove(i);
			}
		}
		fLibrariesList.selectElements(new StructuredSelection(selElements));
	}	
}