regex - Java : Checking if 2 text-paragraphs are different giving error at delete sentence -

i working on java application note-taking. now, whenever user edits text in note, want find difference between oldtext , newtext can add history of note.

for dividing each paragraph multiple strings splitting them @ dot. comparing sentences in string-list using diff-match-patch.

as of works fine add, edit in text, delete sentence, gives problem.

situation

old text : sentence1, sentence2, sentence3, sentence4 new text : sentence1, sentence3, sentence4. 

but because of that, comparator sees sentence2 replaced sentence3, sentence3 sentence4 , so-on , so-forth.

this not desired behaviour, don't know how remedy situation. post code, kindly let me know how can differences between them properly.

groupnotehistory object in saving oldtext , newtext changes only. hope code understandable.

// below list of oldtext , newtext splitted @ dot.         list<string> oldtextlist = arrays.aslist(mnotes1.getmnotetext().split("(\\.|\\n)"));             list<string> newtextlist = arrays.aslist(mnotes.getmnotetext().split("(\\.|\\n)"));  // calculating size of loop.             int counter = math.max(oldtextlist.size(), newtextlist.size());             string oldstring;             string newstring;             (int current = 0; current < counter; current++) {                 oldstring = "";                 newstring = "";                 if (oldtextlist.size() <= current) {                     oldstring = "";                     newstring = newtextlist.get(current);                  } else if (newtextlist.size() <= current) {                     oldstring = oldtextlist.get(current);                     newstring = "";                 } else { // islinedifferent comes diff_match_patch                     if (islinedifferent(oldtextlist.get(current), newtextlist.get(current))) {                         noedit = true;                         groupnotehistory.setwhathaschanged("textchange");                         oldstring += oldtextlist.get(current);                         newstring += newtextlist.get(current);                     }                 }                  if (oldstring != null && newstring != null) {                     if (!(groupnotehistory.getnewnotetext() == null)) {                         if (!(newstring.isempty())) {                             groupnotehistory.setnewnotetext(groupnotehistory.getnewnotetext() + " " + newstring);                         }                     } else {                         groupnotehistory.setnewnotetext(newstring);                     }                     if (!(groupnotehistory.getoldtext() == null)) {                         if (!(oldstring.isempty())) {                             groupnotehistory.setoldtext(groupnotehistory.getoldtext() + " " + oldstring);                         }                     } else {                         groupnotehistory.setoldtext(oldstring);                     }                 } 

kindly let me know can do. lot. :-)

instead of reinventing wheel can use library, i.e one: https://code.google.com/p/java-diff-utils/

you use it's diffutils.diff method adding sentences input, should want achieve, see test below.

import difflib.delta; import difflib.diffutils; import difflib.patch; import org.junit.test;  import java.util.arrays;  public class diffutilstest {     public string note1 = "sentence 1, sentence 2, sentence 3, sentence 4";     public string note2 = "sentence 1, sentence 3, sentence 5";      @test     public void testdiff() {         patch<string> patch = diffutils.diff(arrays.aslist(note1.split("[\\.,]")), arrays.aslist(note2.split("[\\.,]")));          (delta<string> delta: patch.getdeltas()) {             system.out.println(delta);         };         //outputs         //[deletedelta, position: 1, lines: [ sentence 2]]         //[changedelta, position: 3, lines: [ sentence 4] [ sentence 5]]      } }