org.eclipse.jgit.diff

Class SimilarityIndex

java.lang.Object

org.eclipse.jgit.diff.SimilarityIndex

public class SimilarityIndex
extends Object

Index structure of lines/blocks in one file.

This structure can be used to compute an approximation of the similarity between two files. The index is used by SimilarityRenameDetector to compute scores between files.

To save space in memory, this index uses a space efficient encoding which will not exceed 1 MiB per instance. The index starts out at a smaller size (closer to 2 KiB), but may grow as more distinct blocks within the scanned file are discovered.

Since:

4.0

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	SimilarityIndex.TableFullException Thrown by create() when file is too large.

Field Summary

Fields

Modifier and Type	Field and Description
static SimilarityIndex.TableFullException	TABLE_FULL_OUT_OF_MEMORY A special SimilarityIndex.TableFullException used in place of OutOfMemoryError.

Method Summary

Modifier and Type	Method and Description
static SimilarityIndex	create(ObjectLoader obj) Create a new similarity index for the given object
int	score(SimilarityIndex dst, int maxScore) Compute the similarity score between this index and another.

Methods inherited from class java.lang.Object

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

Field Detail

TABLE_FULL_OUT_OF_MEMORY

public static final SimilarityIndex.TableFullException TABLE_FULL_OUT_OF_MEMORY

A special SimilarityIndex.TableFullException used in place of OutOfMemoryError.

Method Detail

create

public static SimilarityIndex create(ObjectLoader obj)
                              throws IOException,
                                     SimilarityIndex.TableFullException

Create a new similarity index for the given object

Parameters:

obj - the object to hash

Returns:

similarity index for this object

Throws:

IOException - file contents cannot be read from the repository.

SimilarityIndex.TableFullException - object hashing overflowed the storage capacity of the SimilarityIndex.

score

public int score(SimilarityIndex dst,
                 int maxScore)

Compute the similarity score between this index and another.

A region of a file is defined as a line in a text file or a fixed-size block in a binary file. To prepare an index, each region in the file is hashed; the values and counts of hashes are retained in a sorted table. Define the similarity fraction F as the count of matching regions between the two files divided between the maximum count of regions in either file. The similarity score is F multiplied by the maxScore constant, yielding a range [0, maxScore]. It is defined as maxScore for the degenerate case of two empty files.

The similarity score is symmetrical; i.e. a.score(b) == b.score(a).

Parameters:

dst - the other index

maxScore - the score representing a 100% match

Returns:

the similarity score