How to perform string Diffs in Java?

Question

I need to perform Diffs between Java strings. I would like to be able to rebuild a string using the original string and diff versions. Has anyone done this in Java? What library do you use?

String a1; // This can be a long text
String a2; // ej. above text with spelling corrections
String a3; // ej. above text with spelling corrections and an additional sentence

Diff diff = new Diff();
String differences_a1_a2 = Diff.getDifferences(a,changed_a);
String differences_a2_a3 = Diff.getDifferences(a,changed_a);    
String[] diffs = new String[]{a,differences_a1_a2,differences_a2_a3};
String new_a3 = Diff.build(diffs);
a3.equals(new_a3); // this is true

Also see stackoverflow.com/questions/479654/…

Stewart
– Stewart

2013-06-17 16:40:37 +00:00
Commented Jun 17, 2013 at 16:40 — Stewart
– Stewart, Commented Jun 17, 2013 at 16:40

user7610 · Accepted Answer · 2018-02-19 11:59:26Z

58

This library seems to do the trick: google-diff-match-patch. It can create a patch string from differences and allow to reapply the patch.

edit: Another solution might be to https://code.google.com/p/java-diff-utils/

edited Feb 19, 2018 at 11:59

user7610

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answered Sep 25, 2008 at 10:41

bernardn

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5 Comments

Kerinin Over a year ago

Those are different libs, FWIW

fracz Over a year ago

Maven repository for the google-diff-match-patch is there.

koppor Over a year ago

The actively maintained fork of java-diff-utils seems to be github.com/bkromhout/java-diff-utils

isapir Over a year ago

google-diff-match-patch on github: github.com/GerHobbelt/google-diff-match-patch

golimar Over a year ago

The maintained fork seems to be now github.com/java-diff-utils/java-diff-utils

Paul Whelan · Accepted Answer · 2008-09-25 10:22:22Z

27

Apache Commons has String diff

org.apache.commons.lang.StringUtils

StringUtils.difference("foobar", "foo");

answered Sep 25, 2008 at 10:22

Paul Whelan

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3 Comments

Sergio del Amo Over a year ago

It returns the remainder of the second String, starting from where it's different from the first. Which is not efficient enough for me since i would be working with big texts. See: StringUtils.difference("ab", "abxyz") -> "xyz" StringUtils.difference("ab", "xyzab") -> "xyzab";

Alec Over a year ago

Also beware this gotcha: StringUtils.difference("abc", "") = "" StringUtils.difference("abc", "abc") = ""

PatS Over a year ago

I'm looking for the wdiff (unix command) in Java, see man page at docs.oracle.com/cd/E88353_01/html/E37839/wdiff-1.html, and SO answer here stackoverflow.com/a/17290563/3281336

dnaumenko · Accepted Answer · 2016-02-28 11:41:28Z

4

The java diff utills library might be useful.

edited Feb 28, 2016 at 11:41

answered Jul 18, 2009 at 8:36

dnaumenko

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1 Comment

koppor Over a year ago

The repo github.com/bkromhout/java-diff-utils forked indirectly from the original GitHub repository and is better maintained. Maybe you can join forces there?

Paul Whelan · Accepted Answer · 2008-09-25 10:46:16Z

3

As Torsten Says you can use

org.apache.commons.lang.StringUtils;

System.err.println(StringUtils.getLevenshteinDistance("foobar", "bar"));

answered Sep 25, 2008 at 10:46

Paul Whelan

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3 Comments

Dr. Hans-Peter Störr Over a year ago

Thank you, but getLevenshteinDistance just returns an integer. That's not enough to rebuild the strings.

Paul Whelan Over a year ago

@hstoerr you are correct I must of missed this part in the original question. Long time ago now :)

Constantino Cronemberger Over a year ago

That method is also deprecated.

Alexander · Accepted Answer · 2008-09-25 14:36:44Z

1

If you need to deal with differences between big amounts of data and have the differences efficiently compressed, you could try a Java implementation of xdelta, which in turn implements RFC 3284 (VCDIFF) for binary diffs (should work with strings too).

answered Sep 25, 2008 at 14:36

Alexander

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Comments

Joshua Goldberg · Accepted Answer · 2022-11-16 16:02:59Z

1

I found it useful to discover, (for a regression test, where I didn't need diffing support in production) that assertj provides built-in access for java-diff-utils. See its DiffUtils, InputStream, or Diff classes, for example.

answered Nov 16, 2022 at 16:02

Joshua Goldberg

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Comments

Torsten Marek · Accepted Answer · 2008-09-25 10:40:02Z

0

Use the Levenshtein distance and extract the edit logs from the matrix the algorithm builds up. The Wikipedia article links to a couple of implementations, I'm sure there's a Java implementation among in.

Levenshtein is a special case of the Longest Common Subsequence algorithm, you might also want to have a look at that.

answered Sep 25, 2008 at 10:40

Torsten Marek

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Comments

Ahmed Ashour · Accepted Answer · 2020-02-12 14:58:11Z

0

Apache Commons Text now has StringsComparator:

StringsComparator c = new StringsComparator(s1, s2);
c.getScript().visit(new CommandVisitor<Character>() {

    @Override
    public void visitKeepCommand(Character object) {
        System.out.println("k: " + object);
    }

    @Override
    public void visitInsertCommand(Character object) {
        System.out.println("i: " + object);
    }

    @Override
    public void visitDeleteCommand(Character object) {
        System.out.println("d: " + object);
    }
});

answered Feb 12, 2020 at 14:58

Ahmed Ashour

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Comments

Sandeep Raj Urs · Accepted Answer · 2016-11-29 18:30:26Z

-7

public class Stringdiff {
public static void main(String args[]){
System.out.println(strcheck("sum","sumsum"));
}
public static String strcheck(String str1,String str2){
    if(Math.abs((str1.length()-str2.length()))==-1){
        return "Invalid";
    }
    int num=diffcheck1(str1, str2);
    if(num==-1){
        return "Empty";
    }
    if(str1.length()>str2.length()){
        return str1.substring(num);
    }
    else{
        return str2.substring(num);
    }

}

public static int diffcheck1(String str1,String str2)
{
    int i;
    String str;
    String strn;
    if(str1.length()>str2.length()){
        str=str1;
        strn=str2;
    }
    else{
        str=str2;
        strn=str1;
    }
    for(i=0;i<str.length() && i<strn.length();i++){
            if(str1.charAt(i)!=str2.charAt(i)){
                return i;
            }
    }
        if(i<str1.length()||i<str2.length()){
            return i;
        }

    return -1;

   }
   }

answered Nov 29, 2016 at 18:30

Sandeep Raj Urs

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1 Comment

Kalle Richter Over a year ago

Untested plain text code like this almost never makes sense. Create a project on a FLOSS code hosting page and provide the code + tests there.

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