Counting the number of occurences of characters in a string

Question

I am trying to write a Java program which takes in as input a string and counts the number of occurrences of characters in a string and then prints a new string having the character followed by the no of occurrences  E G  Input String  aaaabb  Output String  a4b2  Input String  aaaaabbbc  Output String  a5b3c1  I am posting my java code  It is throwing StringOutOfBoundException   Write a routine that takes as input a string such as  quot aabbccdef quot  and o p  quot a2b2c2def quot  or  quot a4bd2g4 quot  for  quot aaaabddgggg quot      import java util Scanner   public class CountingOccurences    public static void main String   args         Scanner inp  new Scanner System in       String str      char ch      int count 0           System out println  quot Enter the string  quot        str inp nextLine             while str length   gt 0                ch str charAt 0           int i 0                   while str charAt i   ch                            count  count i                  i                               str substring count           System out println ch           System out println count

User · Answer

You should be able to utilize the StringUtils class and the countMatches   method      public static int countMatches String str                                   String sub   Counts how many times the substring appears in the larger String     Try the following   int count   StringUtils countMatches  a b c d

User · Answer

I don t want to give out the full code  So I want to give you the challenge and have fun with it  I encourage you to make the code simpler and with only 1 loop   Basically  my idea is to pair up the characters comparison  side by side  For example  compare char 1 with char 2  char 2 with char 3  and so on  When char N not the same with char  N 1  then reset the character count  You can do this in one loop only  While processing this  form a new string  Don t use the same string as your input  That s confusing   Remember  making things simple counts  Life for developers is hard enough looking at complex code   Have fun   Tommy  I should be a Teacher  Kwee

User · Answer

if this is a real program and not a study project  then look at using the Apache Commons StringUtils class - particularly the countMatches method   If it is a study project then keep at it and learn from your exploring

User · Answer

This is the problem   while str charAt i   ch    That will keep going until it falls off the end    when i is the same as the length of the string  it will be asking for a character beyond the end of the string  You probably want   while  i  lt  str length    amp  amp  str charAt i     ch    You also need to set count to 0 at the start of each iteration of the bigger loop - the count resets  after all - and change  count   count   i    to either   count          or get rid of count or i  They re always going to have the same value  after all  Personally I d just use one variable  declared and initialized inside the loop  That s a general style point  in fact - it s cleaner to declare local variables when they re needed  rather than declaring them all at the top of the method   However  then your program will loop forever  as this doesn t do anything useful   str substring count     Strings are immutable in Java - substring returns a new string  I think you want   str   str substring count     Note that this will still output  a2b2a2  for  aabbaa   Is that okay

User · Answer

public class StringTest  public static void main String   args        String s   aaabbbbccccccdd       String result         StringBuilder sb   new StringBuilder s         while sb length      0           int count   0          char test   sb charAt 0           while sb indexOf test        -1               sb deleteCharAt sb indexOf test                   count                        System out println test   is repeated   count   number of times            result result test count            System out println result

User · Answer

Try this   import java util Scanner          Logic  Consider first character in the string and start counting occurrence of                       this character in the entire string  Now add this character to a empty               string  temp  to keep track of the already counted characters                Next start counting from next character and start counting the character                       only if it is not present in the  temp  string  which means only if it is               not counted already  public class Counting Occurences        public static void main String   args              Scanner input new Scanner System in           System out println  Enter String            String str input nextLine             int count 0          String temp        An empty string to keep track of counted                                        characters           for int i 0 i lt str length   i                           char c str charAt i       take one character  c  in string              for int j i j lt str length   j                                   char k str charAt j            take one character  c  and compare with each character  k  in the string                also check that character  c  is not already counted                 if condition passes then increment the count                  if c  k  amp  amp  temp indexOf c   -1                                                                                                                   count count 1                                                  if temp indexOf c   -1      if it is not already counted                              temp temp c     append the character to the temp indicating                                             that you have already counted it   System out println  Character       c       occurs       count        times                                    reset the counter for next iteration                count 0

User · Answer

I think what you are looking for is this   public class Ques2            param args the command line arguments     public static void main String   args  throws IOException       BufferedReader br   new BufferedReader new InputStreamReader System in        String input   br readLine   toLowerCase        StringBuilder result   new StringBuilder        char currentCharacter      int count       for  int i   0  i  lt  input length    i              currentCharacter   input charAt i           count   1          while  i  lt  input length   - 1  amp  amp  input charAt i   1     currentCharacter                count                i                      result append currentCharacter           result append count              System out println      result

[java] Counting the number of occurences of characters in a string

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