JHotDraw Pattern Language

Using Locators

Locators are used to represent (relative) positions on figures. They are useful for defining where handles or connectors should be placed on a figure.

The Locator interface is implemented by AbstractLocator which in turn defines two subclasses, OffsetLocator and RelativeLocator.

Relative Locator is used to represent positions relative to a figures boundary. Positions are specified as percentages of the figure (i.e. 50% along and 50% down will locate the centre of the figure). Relative Locator comes with a set of convenient static methods that specify the ‘compass points’ on a figure (i.e. northWest() specifies the top left hand corner of a figure, etc.)

Offset Locator is used to specify a position relative to another locator. They are often used in conjunction with relative locators, for example to specify a point a few pixels off of the centre of a figure.


Copyright Douglas KIrk