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
* on hash value.
		 */
		protected static class ReverseMap {
			static class Entry {
				Position fPosition;
				Object fValue;
			}
			private List fList= new ArrayList(2);
			private int fAnchor= 0;
			public ReverseMap() {
			}
			public Object get(Position position) {
				Entry entry;
				
				int length= fList.size();
				for (int i= fAnchor; i < length; i++) {
					entry= (Entry) fList.get(i);
					if (entry.fPosition.equals(position)) {
						fAnchor= i;
						return entry.fValue;
					}
				}
				
				for (int i= 0; i < fAnchor; i++) {
					entry= (Entry) fList.get(i);
					if (entry.fPosition.equals(position)) {
						fAnchor= i;
						return entry.fValue;
					}
				}