StringDiff

This java application highlights text differences between two plain strings by generating html fragment to show changes.

The buildLcsList() method finds longest substrings common to both text1 and text2 recursively producing a list of longest common substrings used in markTextDiff() to markup changes between text1 and text2.

Java 8 or later is required to run the application.

Compile

Run following command to build the application:

javac lcs\StringDiff.java

Run

Just use the following command to run the application:

java lcs.StringDiff

Example

Setting the following strings:

text1 = "Do not change this section. Please check any misqelling! Note that this section is obsolete.";
text2 = "New section added. Do not change this section. Please check any mispelling!";

running the command "java lcs.StringDiff" will generate the following html fragment:

<ins style='background-color:#00ff66'>New section added. </ins>Do not change this section. Please check any mis<del style='background-color:#ff9933'>q</del><ins style='background-color:#00ff66'>p</ins>elling!<del style='background-color:#ff9933'> Note that this section is obsolete.</del>

If you load the html fragment with a browser, you get the following result:

Credits

The longest common substrings are found using the LongestCommonSubstring (LCS) algorithm credited to https://algs4.cs.princeton.edu/code/edu/princeton/cs/algs4/LongestCommonSubstring.java.html

Credits go to Robert Sedgewick and Kevin Wayne that provide the LCS algorithm with GNU General Public License

Caveat

This algorithm based on LCS works well with ordinary texts. In case of specific domains it may produce sub-optimal results.

As an example, consider the string "abceabceabce". If we remove the second 'b' letter, we get the string "abceaceabce". Using the LCS algorithm on these two strings, we get "ceabce" as LCS, i.e. the result from markTextDiff() is "abceaceabceabce", instead the optimal result should be "abceabceabce".