private DifferenceEngineContract getDifferenceEngine ( ) { if ( differenceEngine == null ) { if ( XMLUnit . getIgnoreAttributeOrder ( ) && ( ! usesUnknownElementQualifier ( ) || XMLUnit . getCompareUnmatched ( ) ) ) { return new NewDifferenceEngine ( this , matchTrackerDelegate ) ; } return new DifferenceEngine ( this , matchTrackerDelegate ) ; } return differenceEngine ; }
Lazily initializes the difference engine if it hasn t been set via a constructor .