Bug 24199 New Classpath Variables
Why should a full rebuild of the workspace be required when you add a classpath variable? Because it's a new variable it doesn't affect any existing projects. It would be more convenient if a rebuild were not required when adding a new classpath variable. Thanks.
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/wizards/buildpaths/VariableBlock.java
private List fToRemove;
		private List fToChange;
		private boolean fDoBuild;
		
		public VariableBlockRunnable(List toRemove, List toChange, boolean doBuild) {
			fToRemove= toRemove;
			fToChange= toChange;
			fDoBuild= doBuild;
		}
		
		/*
	 	 * @see IRunnableWithProgress#run(IProgressMonitor)
		 */
		public void run(IProgressMonitor monitor) throws InvocationTargetException, InterruptedException {
			monitor.beginTask(NewWizardMessages.getString("VariableBlock.operation_desc"), fDoBuild ? 2 : 1); 
			try {
				int nVariables= fToChange.size() + fToRemove.size();