Occurrences of substring in a string

Question

Why is the following algorithm not halting for me   str is the string I am searching in  findStr is the string I am trying to find   String str    helloslkhellodjladfjhello   String findStr    hello   int lastIndex   0  int count   0   while  lastIndex    -1        lastIndex   str indexOf findStr lastIndex        if  lastIndex    -1          count         lastIndex    findStr length       System out println count

User · Answer

Your lastIndex    findStr length    was placed outside the brackets  causing an infinite loop  when no occurence was found  lastIndex was always to findStr length       Here is the fixed version    String str    helloslkhellodjladfjhello   String findStr    hello   int lastIndex   0  int count   0   while  lastIndex    -1         lastIndex   str indexOf findStr  lastIndex        if  lastIndex    -1            count            lastIndex    findStr length            System out println count

User · Answer

public static int getCountSubString String str   String sub   int n   0  m   0  counter   0  counterSub   0  while n  lt  str length       counter   0    m   0    while m  lt  sub length    amp  amp  str charAt n     sub charAt m        counter        m    n          if  counter    sub length         counterSub        continue        else if counter  gt  0       continue        n       return  counterSub

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Based on the existing answer s  I d like to add a  shorter  version without the if   String str    helloslkhellodjladfjhello   String findStr    hello    int count   0  lastIndex   0  while  lastIndex   str indexOf findStr  lastIndex      -1        lastIndex    findStr length   - 1      count       System out println count      output  3

User · Answer

String str    helloslkhellodjladfjhello   String findStr    hello   int lastIndex   0  int count   0   while  lastIndex   str indexOf findStr  lastIndex      -1         count         lastIndex    findStr length   - 1    System out println count     at the end of the loop count is 3  hope it helps

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If you need the index of each substring within the original string  you can do something with indexOf like this    private static List lt Integer gt  getAllIndexesOfSubstringInString String fullString  String substring        int pointIndex   0      List lt Integer gt  allOccurences   new ArrayList lt Integer gt         while fullPdfText indexOf substring pointIndex   gt   0          allOccurences add fullPdfText indexOf substring  pointIndex           pointIndex   fullPdfText indexOf substring  pointIndex    substring length              return allOccurences

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Here it is  wrapped up in a nice and reusable method   public static int count String text  String find            int index   0  count   0  length   find length            while   index   text indexOf find  index      -1                                     index    length  count                      return count

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This solution prints the total number of occurrence of a given substring throughout the string  also includes the cases where overlapping matches do exist   class SubstringMatch      public static void main String   args             String str    aaaaabaabdcaa             String sub    aa             String str    caaab             String sub    aa           String str  abababababaabb           String sub    bab            int n   str length            int m   sub length                index -1 in case of no match  otherwise  gt  0 first match position          int index str indexOf sub   i index 1  count  index gt  0  1 0          System out println i     index     count               i will traverse up to only  m-n  position         while index  -1  amp  amp  i lt   n-m                   index str substring i  n  indexOf sub               count  index gt  0  count 1 count              i i index 1                System out println i     index                     System out println  count    count

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This below method show how many time substring repeat on ur whole string  Hope use full to you -      String searchPattern  aaa      search string     String str  aaaaaababaaaaaa      whole string     int searchLength   searchPattern length         int totalLength   str length         int k   0      for  int i   0  i  lt  totalLength - searchLength   1  i              String subStr   str substring i  searchLength   i           if  subStr equals searchPattern                k

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You can number of occurrences using inbuilt library function   import org springframework util StringUtils  StringUtils countOccurrencesOf result   R-

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public int countOfOccurrences String str  String subStr      return  str length   - str replaceAll Pattern quote subStr       length      subStr length

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Do you really have to handle the matching yourself   Especially if all you need is the number of occurences  regular expressions are tidier    String str    helloslkhellodjladfjhello   Pattern p   Pattern compile  hello    Matcher m   p matcher str   int count   0  while  m find         count   1    System out println count

User · Answer

Try this one  It replaces all the matches with a -   String str    helloslkhellodjladfjhello   String findStr    hello   int numberOfMatches   0  while  str contains findStr        str   str replaceFirst findStr   -        numberOfMatches        And if you don t want to destroy your str you can create a new string with the same content   String str    helloslkhellodjladfjhello   String strDestroy   str  String findStr    hello   int numberOfMatches   0  while  strDestroy contains findStr        strDestroy   strDestroy replaceFirst findStr   -        numberOfMatches        After executing this block these will be your values   str    helloslkhellodjladfjhello  strDestroy    -slk-djladfj-  findStr    hello  numberOfMatches   3

User · Answer

here is the other solution without using regexp patterns matchers  or even not using StringUtils   String str    helloslkhellodjladfjhelloarunkumarhelloasdhelloaruhelloasrhello           String findStr    hello           int count  0          int findStrLength   findStr length            for int i 0 i lt str length   i                 if findStr startsWith Character toString str charAt i                      if str substring i  length    gt   findStrLength                       if str substring i  i findStrLength  equals findStr                            count                                                                            System out println count

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A lot of the given answers fail on one or more of    Patterns of arbitrary length Overlapping matches  such as counting  232  in  23232  or  aa  in  aaa   Regular expression meta-characters   Here s what I wrote   static int countMatches Pattern pattern  String string        Matcher matcher   pattern matcher string        int count   0      int pos   0      while  matcher find pos                 count            pos   matcher start     1             return count      Example call   Pattern pattern   Pattern compile  232    int count   countMatches pattern   23232       Returns 2   If you want a non-regular-expression search  just compile your pattern appropriately with the LITERAL flag   Pattern pattern   Pattern compile  1 1   Pattern LITERAL   int count   countMatches pattern   1 1 1       Returns 2

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The last line was creating a problem  lastIndex would never be at -1  so there would be an infinite loop  This can be fixed by moving the last line of code into the if block   String str    helloslkhellodjladfjhello   String findStr    hello   int lastIndex   0  int count   0   while lastIndex    -1        lastIndex   str indexOf findStr lastIndex        if lastIndex    -1           count             lastIndex    findStr length            System out println count

User · Answer

Increment lastIndex whenever you look for next occurrence    Otherwise it s always finding the first substring  at position 0

User · Answer

try adding lastIndex  findStr length   to the end of your loop  otherwise you will end up in an endless loop because once you found the substring  you are trying to find it again and again from the same last position

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As  Mr and Mrs D suggested   String haystack    hellolovelyworld   String needle    lo   return haystack split Pattern quote needle   -1  length - 1

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How about using StringUtils countMatches from Apache Commons Lang   String str    helloslkhellodjladfjhello   String findStr    hello    System out println StringUtils countMatches str  findStr      That outputs   3

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I m very surprised no one has mentioned this one liner  It s simple  concise and performs slightly better than str split target  -1  length-1  public static int count String str  String target        return  str length   - str replace target      length      target length

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public int indexOf int ch                     int fromIndex    Returns the index within this string of the first occurrence of the specified character  starting the search at the specified index   So your lastindex value is always 0 and it always finds hello in the string

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The answer given as correct is no good for counting things like line returns and is far too verbose  Later answers are better but all can be achieved simply with  str split findStr  length   It does not drop trailing matches using the example in the question

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Here is the advanced version for counting how many times the token occurred in a user entered string   public class StringIndexOf        public static void main String   args             Scanner scanner   new Scanner System in            System out println  Enter a sentence please   n            String string   scanner nextLine             int atIndex   0          int count   0           while  atIndex    -1                        atIndex   string indexOf  hello   atIndex                if atIndex    -1                                count                    atIndex    5                                   System out println count

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A shorter version      String str    helloslkhellodjladfjhello   String findStr    hello   System out println str split findStr  -1  length-1

[java] Occurrences of substring in a string

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