Package ca.cgjennings.algo

Class Diff<E>

  • Type Parameters:
    E - the type of the elements that may be inserted, deleted, or changed; for example, in a text file each element might be a String representing a single line
    public class Diff<E>
extends java.lang.Object
    A generic implementation of the diff algorithm. This algorithm describes the changes needed to convert one sequence of objects into another. It is most commonly used to determine the changes between two text files by comparing their lines.

    The algorithm is used in combination with a DiffListener. The listener's methods will be called in the order of the original sequence and will describe a combined version of both the original and changed sequences, with insertions and deletions at the appropriate points in order to describe the actions that would covert the original sequence to the new sequence in the minimal number of steps.

    Since:
    2.0
    Author:
    Chris Jennings

    • Constructor Summary

      Constructors 
      Constructor Description
      Diff()
      Create a new Diff instance that uses a default listener that is useful for diagnostic purposes.
      Diff​(DiffListener<E> listener)
      A diff engine that posts differences to the specified listener.

    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      boolean equal​(E a, E b, int originalIndex, int changedIndex)
      The method used to compare two entries for equality.
      void findChanges​(E[] original, E[] changed)
      Determine the difference between the original and changed element sequences, posting them to the listener supplied at construction.

      • Methods inherited from class java.lang.Object

        clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

    • Constructor Detail

      • Diff

        public Diff()
        Create a new Diff instance that uses a default listener that is useful for diagnostic purposes. For each element in the combined collection, this listener prints to the output stream one of the following followed by the string value of the element in question:
        "> "
        this element must be inserted
        "X "
        this element must be deleted
        "  "
        this element is unchanged
        This listener prints the string value of each element from the combined collection

      • Diff

        public Diff​(DiffListener<E> listener)
        A diff engine that posts differences to the specified listener.
        Parameters:
        listener - a listener to be notified of the sequence of changes required to modify the original version of an entity to the changed version

    • Method Detail

      • findChanges

        public void findChanges​(E[] original,
                        E[] changed)
        Determine the difference between the original and changed element sequences, posting them to the listener supplied at construction.
        Parameters:
        original - the original sequence of elements
        changed - the changed sequence of elements

      • equal

        public boolean equal​(E a,
                     E b,
                     int originalIndex,
                     int changedIndex)
        The method used to compare two entries for equality. The default implementation is equivalent to: 
         if( a == null ) {
     return b == null;
 } else {
     return a.equals( b );
 }
        Parameters:
        a - an item from the original collection being compared
        b - an item from the changed collection being compared
        originalIndex - the index of a in the original sequence
        changedIndex - the index of b in the changed sequence
        Returns:
        true if the objects should be considered equal for the purposes of the diff operation