Diffable classes can be compared with other objects for differences. The DiffResult object retrieved can be queried for a list of differences or printed using the DiffResult#toString().

The calculation of the differences is consistent with equals if and only if d1.equals(d2) implies d1.diff(d2) == "". It is strongly recommended that implementations are consistent with equals to avoid confusion. Note that null is not an instance of any class and d1.diff(null) should throw a NullPointerException.

Diffable classes lend themselves well to unit testing, in which a easily readable description of the differences between an anticipated result and an actual result can be retrieved. For example:

Assert.assertEquals(expected.diff(result), expected, result);