Bug 54900 [rulers] Java Editor does not show ruler on external Java files
org.eclipse.jdt.ui/ui/org/eclipse/jdt/internal/ui/javaeditor/CompilationUnitDocumentProvider.java
return null;
			}
			private int getIndex(Position position) {
				Entry entry;
				int length= fList.size();
				for (int i= 0; i < length; i++) {
					entry= (Entry) fList.get(i);
					if (entry.fPosition.equals(position))
						return i;
				}
				return -1;
			}
			public void put(Position position,  Object value) {
				int index= getIndex(position);
				if (index == -1) {
					Entry entry= new Entry();
					entry.fPosition= position;
					entry.fValue= value;
					fList.add(entry);
				} else {
					Entry entry= (Entry) fList.get(index);
					entry.fValue= value;
				}
			}
			public void remove(Position position) {
				int index= getIndex(position);
				if (index > -1)
					fList.remove(index);
			}
			public void clear() {