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Java methods can be overloaded (i.e. allow for multi-valued declaration with various argument patterns -- see e.g. move() method) in a similar way as class constructors.
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Canvas inherits move() method, and overrides inverse() method (by adding color inversion, i.e. "inverse video").
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paint() method operates on Graphics object from Sun's Java class library which is included via the import statement.
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We used the interface construct to separate 2D translational degrees of freedoms (which are handled as Movable methods) from the internal coordinates (which are handled by individual classes).
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Note that interfaces can only contain static (global) variables (here, x=0.0, y=0.0 which is the default origin for Point() constructor).
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This allows one to avoid the usual ambiguities with multiply inherited instance variables in case of closed loops in the inheritance graph.
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