Class Differencer


  • public class Differencer
    extends Object
    A generic two-way or three-way differencing engine.

    The engine is used by calling one of the findDifferences methods and passing in the objects to compare. The engine calls the following methods on the input objects to perform the compare:

    • getChildren: for enumerating the children of an object (if any),
    • contentsEqual: for comparing the content of leaf objects, that is, objects without children,
    • visit: for every pair of compared object the compare result is passed in.
    Clients may use as is, or subclass to provide a custom implementation for the three hooks. However the default implementation already deals with the typical case:
    • getChildren: tries to apply the IStructureComparator interface to enumerate the children,
    • contentsEqual: tries to apply the IStreamContentAccessor interface to perform a byte-wise content comparison,
    • visit: creates a DiffNode for any detected difference between the compared objects and links it under a parent node effectively creating a tree of differences.
    The different kind of changes detected by the engine are decoded as follows: In the two-way case only NO_CHANGE, ADDITION, DELETION, and CHANGE are used. In the three-way case these constants are bitwise ORed with one of directional constants LEFT, RIGHT, and CONFLICTING.
    • Field Summary

      Fields 
      Modifier and Type Field Description
      static int ADDITION
      Difference constant (value 1) indicating one side was added.
      static int CHANGE
      Difference constant (value 3) indicating side changed.
      static int CHANGE_TYPE_MASK
      Bit mask (value 3) for extracting the kind of difference.
      static int CONFLICTING
      Three-way change constant (value 12) indicating a change on left and right sides.
      static int DELETION
      Difference constant (value 2) indicating one side was removed.
      static int DIRECTION_MASK
      Bit mask (value 12) for extracting the direction of a three-way change.
      static int LEFT
      Three-way change constant (value 4) indicating a change on left side.
      static int NO_CHANGE
      Difference constant (value 0) indicating no difference.
      static int PSEUDO_CONFLICT
      Constant (value 16) indicating a change on left and right side (with respect to ancestor) but left and right are identical.
      static int RIGHT
      Three-way change constant (value 8) indicating a change on right side.
    • Constructor Summary

      Constructors 
      Constructor Description
      Differencer()
      Creates a new differencing engine.
    • Field Detail

      • NO_CHANGE

        public static final int NO_CHANGE
        Difference constant (value 0) indicating no difference.
        See Also:
        Constant Field Values
      • ADDITION

        public static final int ADDITION
        Difference constant (value 1) indicating one side was added.
        See Also:
        Constant Field Values
      • DELETION

        public static final int DELETION
        Difference constant (value 2) indicating one side was removed.
        See Also:
        Constant Field Values
      • CHANGE

        public static final int CHANGE
        Difference constant (value 3) indicating side changed.
        See Also:
        Constant Field Values
      • CHANGE_TYPE_MASK

        public static final int CHANGE_TYPE_MASK
        Bit mask (value 3) for extracting the kind of difference.
        See Also:
        Constant Field Values
      • LEFT

        public static final int LEFT
        Three-way change constant (value 4) indicating a change on left side.
        See Also:
        Constant Field Values
      • RIGHT

        public static final int RIGHT
        Three-way change constant (value 8) indicating a change on right side.
        See Also:
        Constant Field Values
      • CONFLICTING

        public static final int CONFLICTING
        Three-way change constant (value 12) indicating a change on left and right sides.
        See Also:
        Constant Field Values
      • DIRECTION_MASK

        public static final int DIRECTION_MASK
        Bit mask (value 12) for extracting the direction of a three-way change.
        See Also:
        Constant Field Values
      • PSEUDO_CONFLICT

        public static final int PSEUDO_CONFLICT
        Constant (value 16) indicating a change on left and right side (with respect to ancestor) but left and right are identical.
        See Also:
        Constant Field Values
    • Constructor Detail

      • Differencer

        public Differencer()
        Creates a new differencing engine.
    • Method Detail

      • findDifferences

        public Object findDifferences​(boolean threeWay,
                                      IProgressMonitor pm,
                                      Object data,
                                      Object ancestor,
                                      Object left,
                                      Object right)
        Starts the differencing engine on the three input objects. If threeWay is true a three-way comparison is performed, otherwise a two-way compare (in the latter case the ancestor argument is ignored). The progress monitor is passed to the method updateProgress which is called for every node or leaf compare. The method returns the object that was returned from the top-most call to method visit. At most two of the ancestor, left, and right parameters are allowed to be null.
        Parameters:
        threeWay - if true a three-way comparison is performed, otherwise a two-way compare
        pm - a progress monitor which is passed to method updateProgress
        data - a client data that is passed to the top-level call to visit
        ancestor - the ancestor object of the compare (may be null)
        left - the left object of the compare
        right - the right object of the compare
        Returns:
        the object returned from the top most call to method visit, possibly null
      • visit

        protected Object visit​(Object data,
                               int result,
                               Object ancestor,
                               Object left,
                               Object right)
        Called for every node or leaf comparison. The differencing engine passes in the input objects of the compare and the result of the compare. The data object is the value returned from a call to the visit method on the parent input. It can be considered the "parent" reference and is useful when building a tree.

        The Differencer implementation returns a new DiffNode which is initialized with the corresponding values. Subclasses may override.

        Parameters:
        data - object returned from parent call to visit, possibly null
        result - the result of the compare operation performed on the three inputs
        ancestor - the compare ancestor of the left and right inputs
        left - the left input to the compare
        right - the right input to the compare
        Returns:
        the result, possibly null
      • contentsEqual

        protected boolean contentsEqual​(Object input1,
                                        char contributor1,
                                        Object input2,
                                        char contributor2)
        Performs a content compare on the two given inputs.

        The Differencer implementation returns contentsEqual(Object input1, Object input2). Subclasses may override to implement a different content compare on the given inputs.

        Parameters:
        input1 - first input to contents compare
        contributor1 - the contributor of input1
        input2 - second input to contents compare
        contributor2 - the contributor of input2
        Returns:
        true if content is equal
        Since:
        3.6
        Restriction:
        This method is not intended to be referenced by clients.
      • contentsEqual

        protected boolean contentsEqual​(Object input1,
                                        Object input2)
        Performs a content compare on the two given inputs.

        The Differencer implementation returns true if both inputs implement IStreamContentAccessor and their byte contents is identical. Subclasses may override to implement a different content compare on the given inputs.

        Parameters:
        input1 - first input to contents compare
        input2 - second input to contents compare
        Returns:
        true if content is equal
      • getChildren

        protected Object[] getChildren​(Object input)
        Returns the children of the given input or null if there are no children.

        The Differencer implementation checks whether the input implements the IStructureComparator interface. If yes it is used to return an array containing all children. Otherwise null is returned. Subclasses may override to implement a different strategy to enumerate children.

        Parameters:
        input - the object for which to return children
        Returns:
        the children of the given input or null if there are no children.
      • updateProgress

        protected void updateProgress​(IProgressMonitor progressMonitor,
                                      Object node)
        Called for every leaf or node compare to update progress information.

        The Differencer implementation shows the name of the input object as a subtask. Subclasses may override.

        Parameters:
        progressMonitor - the progress monitor for reporting progress
        node - the currently processed non-null node