com.jaxfront.core.util.diff
Class DiffTool

java.lang.Object
  com.jaxfront.core.util.diff.DiffTool

public class DiffTool
extends java.lang.Object

A class to compare vectors of objects. The result of comparison is a list of change objects which form an edit script. The objects compared are traditionally lines of text from two files. Comparison options such as "ignore whitespace" are implemented by modifying the equals and hashcode methods for the objects compared.

The basic algorithm is described in:
"An O(ND) Difference Algorithm and its Variations", Eugene Myers, Algorithmica Vol. 1 No. 2, 1986, p 251.

This class outputs different results from GNU diff 1.15 on some inputs. Our results are actually better (smaller change list, smaller total size of changes), but it would be nice to know why. Perhaps there is a memory overwrite bug in GNU diff 1.15.

Nested Class Summary

static class	DiffTool.change The result of comparison is an "edit script": a chain of change objects.
static interface	DiffTool.ScriptBuilder

Field Summary

static DiffTool.ScriptBuilder	forwardScript Standard ScriptBuilders.
boolean	heuristic When set to true, the comparison uses a heuristic to speed it up.
boolean	no_discards When set to true, the algorithm returns a guarranteed minimal set of changes.
static DiffTool.ScriptBuilder	reverseScript Standard ScriptBuilders.

Constructor Summary

DiffTool(java.lang.Object[] a, java.lang.Object[] b)
Prepare to find differences between two arrays.

Method Summary

DiffTool.change	diff_2(boolean reverse)
DiffTool.change	diff(DiffTool.ScriptBuilder bld) Get the results of comparison as an edit script.

Methods inherited from class java.lang.Object

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

Field Detail

forwardScript

public static final DiffTool.ScriptBuilder forwardScript

Standard ScriptBuilders.

heuristic

public boolean heuristic

When set to true, the comparison uses a heuristic to speed it up. With this heuristic, for files with a constant small density of changes, the algorithm is linear in the file size.

no_discards

public boolean no_discards

When set to true, the algorithm returns a guarranteed minimal set of changes. This makes things slower, sometimes much slower.

reverseScript

public static final DiffTool.ScriptBuilder reverseScript

Standard ScriptBuilders.

Constructor Detail

DiffTool

public DiffTool(java.lang.Object[] a,
                java.lang.Object[] b)

Prepare to find differences between two arrays. Each element of the arrays is translated to an "equivalence number" based on the result of equals. The original Object arrays are no longer needed for computing the differences. They will be needed again later to print the results of the comparison as an edit script, if desired.

Method Detail

diff_2

public final DiffTool.change diff_2(boolean reverse)

diff

public DiffTool.change diff(DiffTool.ScriptBuilder bld)

Get the results of comparison as an edit script. The script is described by a list of changes. The standard ScriptBuilder implementations provide for forward and reverse edit scripts. Alternate implementations could, for instance, list common elements instead of differences.

Parameters:

bld - an object to build the script from change flags

Returns:

the head of a list of changes