Class SequencesComparator<T>


  • public class SequencesComparator<T>
    extends java.lang.Object
    This class allows to compare two objects sequences.

    The two sequences can hold any object type, as only the equals method is used to compare the elements of the sequences. It is guaranteed that the comparisons will always be done as o1.equals(o2) where o1 belongs to the first sequence and o2 belongs to the second sequence. This can be important if subclassing is used for some elements in the first sequence and the equals method is specialized.

    Comparison can be seen from two points of view: either as giving the smallest modification allowing to transform the first sequence into the second one, or as giving the longest sequence which is a subsequence of both initial sequences. The equals method is used to compare objects, so any object can be put into sequences. Modifications include deleting, inserting or keeping one object, starting from the beginning of the first sequence.

    This class implements the comparison algorithm, which is the very efficient algorithm from Eugene W. Myers An O(ND) Difference Algorithm and Its Variations. This algorithm produces the shortest possible edit script containing all the commands needed to transform the first sequence into the second one.

    Since:
    4.0
    See Also:
    EditScript, EditCommand, CommandVisitor
    • Nested Class Summary

      Nested Classes 
      Modifier and Type Class Description
      private static class  SequencesComparator.Snake
      This class is a simple placeholder to hold the end part of a path under construction in a SequencesComparator.
    • Field Summary

      Fields 
      Modifier and Type Field Description
      private Equator<? super T> equator
      The equator used for testing object equality.
      private java.util.List<T> sequence1
      First sequence.
      private java.util.List<T> sequence2
      Second sequence.
      private int[] vDown
      Temporary variables.
      private int[] vUp  
    • Constructor Summary

      Constructors 
      Constructor Description
      SequencesComparator​(java.util.List<T> sequence1, java.util.List<T> sequence2)
      Simple constructor.
      SequencesComparator​(java.util.List<T> sequence1, java.util.List<T> sequence2, Equator<? super T> equator)
      Simple constructor.
    • Field Detail

      • sequence1

        private final java.util.List<T> sequence1
        First sequence.
      • sequence2

        private final java.util.List<T> sequence2
        Second sequence.
      • equator

        private final Equator<? super T> equator
        The equator used for testing object equality.
      • vDown

        private final int[] vDown
        Temporary variables.
      • vUp

        private final int[] vUp
    • Constructor Detail

      • SequencesComparator

        public SequencesComparator​(java.util.List<T> sequence1,
                                   java.util.List<T> sequence2)
        Simple constructor.

        Creates a new instance of SequencesComparator using a DefaultEquator.

        It is guaranteed that the comparisons will always be done as o1.equals(o2) where o1 belongs to the first sequence and o2 belongs to the second sequence. This can be important if subclassing is used for some elements in the first sequence and the equals method is specialized.

        Parameters:
        sequence1 - first sequence to be compared
        sequence2 - second sequence to be compared
      • SequencesComparator

        public SequencesComparator​(java.util.List<T> sequence1,
                                   java.util.List<T> sequence2,
                                   Equator<? super T> equator)
        Simple constructor.

        Creates a new instance of SequencesComparator with a custom Equator.

        It is guaranteed that the comparisons will always be done as Equator.equate(o1, o2) where o1 belongs to the first sequence and o2 belongs to the second sequence.

        Parameters:
        sequence1 - first sequence to be compared
        sequence2 - second sequence to be compared
        equator - the equator to use for testing object equality
    • Method Detail

      • getScript

        public EditScript<T> getScript()
        Get the EditScript object.

        It is guaranteed that the objects embedded in the insert commands come from the second sequence and that the objects embedded in either the delete commands or keep commands come from the first sequence. This can be important if subclassing is used for some elements in the first sequence and the equals method is specialized.

        Returns:
        the edit script resulting from the comparison of the two sequences
      • buildSnake

        private SequencesComparator.Snake buildSnake​(int start,
                                                     int diag,
                                                     int end1,
                                                     int end2)
        Build a snake.
        Parameters:
        start - the value of the start of the snake
        diag - the value of the diagonal of the snake
        end1 - the value of the end of the first sequence to be compared
        end2 - the value of the end of the second sequence to be compared
        Returns:
        the snake built
      • getMiddleSnake

        private SequencesComparator.Snake getMiddleSnake​(int start1,
                                                         int end1,
                                                         int start2,
                                                         int end2)
        Get the middle snake corresponding to two subsequences of the main sequences.

        The snake is found using the MYERS Algorithm (this algorithms has also been implemented in the GNU diff program). This algorithm is explained in Eugene Myers article: An O(ND) Difference Algorithm and Its Variations.

        Parameters:
        start1 - the begin of the first sequence to be compared
        end1 - the end of the first sequence to be compared
        start2 - the begin of the second sequence to be compared
        end2 - the end of the second sequence to be compared
        Returns:
        the middle snake
      • buildScript

        private void buildScript​(int start1,
                                 int end1,
                                 int start2,
                                 int end2,
                                 EditScript<T> script)
        Build an edit script.
        Parameters:
        start1 - the begin of the first sequence to be compared
        end1 - the end of the first sequence to be compared
        start2 - the begin of the second sequence to be compared
        end2 - the end of the second sequence to be compared
        script - the edited script