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org.eclipse.compare.structuremergeviewer
Class Differencer  

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

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public class Differencer

extends java.lang.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.

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Nested Class Summary
(package private) static class	Differencer.Node

 

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
private  int	compare(boolean threeway, java.lang.Object ancestor, java.lang.Object left, java.lang.Object right)           Performs a 2-way or 3-way compare of the given leaf elements and returns an integer describing the kind of difference.
protected  boolean	contentsEqual(java.lang.Object input1, java.lang.Object input2)           Performs a content compare on the two given inputs.
java.lang.Object	findDifferences(boolean threeWay, org.eclipse.core.runtime.IProgressMonitor pm, java.lang.Object data, java.lang.Object ancestor, java.lang.Object left, java.lang.Object right)           Starts the differencing engine on the three input objects.
protected  java.lang.Object[]	getChildren(java.lang.Object input)           Returns the children of the given input or null if there are no children.
private  java.io.InputStream	getStream(java.lang.Object o)           Tries to return an InputStream for the given object.
private  int	traverse(boolean threeWay, Differencer.Node parent, org.eclipse.core.runtime.IProgressMonitor pm, java.lang.Object ancestor, java.lang.Object left, java.lang.Object right)           Traverse tree in postorder.
protected  void	updateProgress(org.eclipse.core.runtime.IProgressMonitor progressMonitor, java.lang.Object node)           Called for every leaf or node compare to update progress information.
protected  java.lang.Object	visit(java.lang.Object data, int result, java.lang.Object ancestor, java.lang.Object left, java.lang.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

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ADDITION

public static final int ADDITION

Difference constant (value 1) indicating one side was added.

See Also:

Constant Field Values

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DELETION

public static final int DELETION

Difference constant (value 2) indicating one side was removed.

See Also:

Constant Field Values

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CHANGE

public static final int CHANGE

Difference constant (value 3) indicating side changed.

See Also:

Constant Field Values

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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

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LEFT

public static final int LEFT

Three-way change constant (value 4) indicating a change on left side.

See Also:

Constant Field Values

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RIGHT

public static final int RIGHT

Three-way change constant (value 8) indicating a change on right side.

See Also:

Constant Field Values

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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

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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

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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 java.lang.Object findDifferences(boolean threeWay,
                                        org.eclipse.core.runtime.IProgressMonitor pm,
                                        java.lang.Object data,
                                        java.lang.Object ancestor,
                                        java.lang.Object left,
                                        java.lang.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.

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traverse

private int traverse(boolean threeWay,
                     Differencer.Node parent,
                     org.eclipse.core.runtime.IProgressMonitor pm,
                     java.lang.Object ancestor,
                     java.lang.Object left,
                     java.lang.Object right)

Traverse tree in postorder.

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visit

protected java.lang.Object visit(java.lang.Object data,
                                 int result,
                                 java.lang.Object ancestor,
                                 java.lang.Object left,
                                 java.lang.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.

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compare

private int compare(boolean threeway,
                    java.lang.Object ancestor,
                    java.lang.Object left,
                    java.lang.Object right)

Performs a 2-way or 3-way compare of the given leaf elements and returns an integer describing the kind of difference.

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contentsEqual

protected boolean contentsEqual(java.lang.Object input1,
                                java.lang.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.

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getStream

private java.io.InputStream getStream(java.lang.Object o)

Tries to return an InputStream for the given object. Returns null if the object not an IStreamContentAccessor or an error occured.

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getChildren

protected java.lang.Object[] getChildren(java.lang.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.

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updateProgress

protected void updateProgress(org.eclipse.core.runtime.IProgressMonitor progressMonitor,
                              java.lang.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.

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Overview  Package   Class  Use  Deprecated  Index
Home >> All >> org >> eclipse >> compare >> [ structuremergeviewer overview ]	PREV CLASS  NEXT CLASS
SUMMARY:  JAVADOC |  SOURCE |  DOWNLOAD | NESTED | FIELD | CONSTR | METHOD	DETAIL: FIELD | CONSTR | METHOD

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