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org.eclipse.compare.structuremergeviewer
Class Differencer

java.lang.Object
  org.eclipse.compare.structuremergeviewer.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

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

Differencer()
Creates a new differencing engine.

Method Summary

protected boolean	contentsEqual(Object input1, Object input2) Performs a content compare on the two given inputs.
Object	findDifferences(boolean threeWay, IProgressMonitor pm, Object data, Object ancestor, Object left, Object right) Starts the differencing engine on the three input objects.
protected Object[]	getChildren(Object input) Returns the children of the given input or null if there are no children.
protected void	updateProgress(IProgressMonitor progressMonitor, Object node) Called for every leaf or node compare to update progress information.
protected Object	visit(Object data, int result, Object ancestor, Object left, Object right) Called for every node or leaf comparison.

Methods inherited from class java.lang.Object

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

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,
                                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

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