You place data tips only by clicking data objects on graphs. You cannot place them programmatically (by executing code to position a data cursor).

Well, this has never stopped us before, has it?

Creating new data tips

Under the hood, data tips use a data-cursor mode, which shares many similarities in behavior and programming code with the other plot modes (zoom, pan, data-brushing, etc.). At any one time, only a single such mode can be active in any figure window (this is a known limitation of the design). The code itself it actually quite complex and handles numerous edge-cases. Understanding it by simply reading the code (under %matlabroot%\toolbox\matlab\graphics\) is actually pretty difficult. A much easier way to understand the programming flow is to liberally distribute breakpoints (start in datacursormode.m) and interactively activate the functionality, then debug the code step-by-step.
Luckily, it turns out that the code to create a new data-tip is actually quite simple: first get the data-cursor mode object, then create a new data tip using the mode’s createDatatip() method, update some data-tip properties and finally update the data-tip’s position:

% First plot the data
hLine = plot(xdata, ydata);
% First get the figure's data-cursor mode, activate it, and set some of its properties
cursorMode = datacursormode(gcf);
set(cursorMode, 'enable','on', 'UpdateFcn',@setDataTipTxt);
% Note: the optional @setDataTipTxt is used to customize the data-tip's content text
% Note: the following code was adapted from %matlabroot%\toolbox\matlab\graphics\datacursormode.m
% Create a new data tip
hTarget = handle(hLine);
hDatatip = cursorMode.createDatatip(hTarget);
% Create a copy of the context menu for the datatip:
set(hDatatip,'UIContextMenu',get(cursorMode,'UIContextMenu'));
set(hDatatip,'HandleVisibility','off');
set(hDatatip,'Host',hTarget);
set(hDatatip,'ViewStyle','datatip');
% Set the data-tip orientation to top-right rather than auto
set(hDatatip,'OrientationMode','manual');
set(hDatatip,'Orientation','top-right');
% Update the datatip marker appearance
set(hDatatip, 'MarkerSize',5, 'MarkerFaceColor','none', ...
              'MarkerEdgeColor','k', 'Marker','o', 'HitTest','off');
% Move the datatip to the right-most data vertex point
position = [xdata(end),ydata(end),1; xdata(end),ydata(end),-1];
update(hDatatip, position);

Note: If you don’t like messing with the code, consider using Tim Farajian’s MakeDataTip utility, which basically does all this behind the scenes. It is much easier to use as a stand-alone utility, although it does not give you the flexiblility with all the data-tip properties as in the code above.

Updating an existing data tip

To modify the appearance of a data-tip, we first need to get access to the hDatatip object that we created earlier, either programmatically, or interactively (or both). Since we can access pre-stored handles only of programmatically-created (not interactively-created) data-tips, we need to use a different method. There are actually two ways to do this:
The basic way is to search the relevant axes for objects that have Tag=’DataTipMarker’. For each data-tip, we will get two such handles: one for the marker (Type=’line’) and the other for the text box tooltip (Type=’text’). We can use these to update (for example) the marker size, color and style; and the text’s font, border and colors.
A better way is to access the graphics.datatip object itself. This can be done using two hidden properties of the datacursormode object:

% Get the list of all data-tips in the current figure
>> cursorMode = datacursormode(gcf)
cursorMode =
	graphics.datacursormanager
>> cursorMode.DataCursors
ans =
	graphics.datatip: 2-by-1
>> cursorMode.CurrentDataCursor
ans =
	graphics.datatip
>> cursorMode.CurrentDataCursor.get
            Annotation: [1x1 hg.Annotation]
           DisplayName: ''
           HitTestArea: 'off'
          BeingDeleted: 'off'
         ButtonDownFcn: []
              Children: [2x1 double]
              Clipping: 'on'
             CreateFcn: []
             DeleteFcn: []
            BusyAction: 'queue'
      HandleVisibility: 'off'
               HitTest: 'off'
         Interruptible: 'on'
                Parent: 492.005493164063
    SelectionHighlight: 'on'
                   Tag: ''
                  Type: 'hggroup'
              UserData: []
              Selected: 'off'
             FontAngle: 'normal'
              FontName: 'Helvetica'
              FontSize: 8
             FontUnits: 'points'
            FontWeight: 'normal'
             EdgeColor: [0.8 0.8 0.8]
       BackgroundColor: [1 1 0.933333333333333]
             TextColor: [0 0 0]
                Marker: 'o'
            MarkerSize: 5
       MarkerEdgeColor: 'k'
       MarkerFaceColor: 'none'
       MarkerEraseMode: 'normal'
             Draggable: 'on'
                String: {'Date: 01/09/11'  'Value: 573.24'}
               Visible: 'on'
             StringFcn: []
             UpdateFcn: []
         UIContextMenu: [1x1 uicontextmenu]
                  Host: [1x1 graph2d.lineseries]
           Interpolate: 'off'

We can see that the returned graphics.datatip object includes properties of both the text-box and the marker, making it easy to modify. Moreover, we can use its aforementioned update method to move the datatip to a different plot position (see example in the code above). In addition, we can also use the self-explanatory getCursorInfo(), getaxes(), makeCurrent(), movetofront() methods, and a few others.

Cursor mode and data-tip properties

The graphics.datacursormanager and the graphics.datatip objects have several public properties that we can use:

>> cursorMode.get
              Enable: 'off'
    SnapToDataVertex: 'on'
        DisplayStyle: 'datatip'
           UpdateFcn: @setDataTipTxt
              Figure: [1x1 figure]
>> cursorMode.CurrentDataCursor.get
            Annotation: [1x1 hg.Annotation]
           DisplayName: ''
           HitTestArea: 'off'
      ... % See the list above

Both these objects have plenty of additional hidden properties. You can inspect them using my uiinspect utility. Here is a brief list for reference (R2011b):
graphics.datacursormanager:

• CurrentDataCursor
• DataCursors
• Debug
• DefaultExportVarName
• DefaultPanelPosition
• EnableAxesStacking
• EnableZStacking
• ExternalListeners
• HiddenUpdateFcn
• NewDataCursorOnClick
• OriginalRenderer
• OriginalRendererMode
• PanelDatatipHandle
• PanelHandle
• PanelTextHandle
• UIContextMenu
• UIState
• ZStackMinimum

graphics.datatip:

• ALimInclude
• ApplicationData
• Behavior
• CLimInclude
• DataCursorHandle
• DataManagerHandle
• Debug
• DoThrowStartDragEvent
• EmptyArgUpdateFcn
• EnableAxesStacking
• EnableZStacking
• EraseMode
• EventObject
• ExternalListenerHandles
• HelpTopicKey
• HostAxes
• HostListenerHandles
• IncludeRenderer
• Invalid
• IsDeserializing
• MarkerHandle
• MarkerHandleButtonDownFcn
• Orientation
• OrientationMode
• OrientationPropertyListener
• OriginalDoubleBufferState
• PixelBounds
• PointsOffset
• Position
• SelfListenerHandles
• Serializable
• TextBoxHandle
• TextBoxHandleButtonDownFcn
• Version
• ViewStyle
• XLimInclude
• YLimInclude
• ZLimInclude
• ZStackMinimum
• uistate

As can be seen, if we really want, we can always use the MarkerHandle or TextBoxHandle directly.

Deleting data tips

To delete a specific data-tip, simply call the cursor mode’s removeDataCursor() method; to delete all data-tips, call its removeAllDataCursors() method:

% Delete the current data-tip
cursorMode.removeDataCursor(cursorMode.CurrentDataCursor)
% Delete all data-tips
cursorMode.removeAllDataCursors()

Have you used plot data-tips in some nifty way? If so, please share your experience in a comment below.
p.s. – did you notice that Java was not mentioned anywhere above? Mode managers use pure-Matlab functionality.

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