Bug 31374 Package Explorer does not show children of linked directories
org.eclipse.jdt.ui/ui/org/eclipse/jdt/ui/StandardJavaElementContentProvider.java
if (element instanceof IPackageFragment) {
			IPackageFragmentRoot parent= (IPackageFragmentRoot)((IPackageFragment)element).getParent();
			return skipProjectPackageFragmentRoot(parent);
		}
		if (element instanceof IJavaElement) {
			IJavaElement candidate= ((IJavaElement)element).getParent();
			
			
			if (candidate != null && candidate.getElementType() == IJavaElement.COMPILATION_UNIT) {
				candidate= JavaModelUtil.toOriginal((ICompilationUnit) candidate);
			}
			return candidate;
		}
		return null;
	}
	
	/**
	 * Note: This method is for internal use only. Clients should not call this method.
	 */
	protected static Object[] concatenate(Object[] a1, Object[] a2) {
		int a1Len= a1.length;
		int a2Len= a2.length;
		Object[] res= new Object[a1Len + a2Len];
		System.arraycopy(a1, 0, res, 0, a1Len);
		System.arraycopy(a2, 0, res, a1Len, a2Len); 
		return res;
	}
}