FindDuplicate.java

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// Java Program to find duplicate characters in a String

public class FindDuplicate {

  public void countDupChars(String str) {

    // here all the checked characters will come
    String checkedChar = "";

    // get all characters available in 'str'
    for (int i = 0; i < str.length(); i++) {

      // get character at 'i' position
      char getCharacter = str.charAt(i);

      /* check if that character is available in 'checkedChar'
       * if available it means that character is already checked before no need to check again*/
      if (checkedChar.indexOf(getCharacter) == -1) {

        int duplicateCount = 0;

        // add character to 'checkedChar'  to prevent re-checking of this character again
        checkedChar = checkedChar + getCharacter;

        /* compare getCharacter's value to all other characters available in 'str'
         * If getCharacter's value matches with any character str then increament duplicateCount's value
         */
        for (int v = 0; v < str.length(); v++) {

          // check if not not same position as getCharacter's position			  
          if (i != v) {

            /* check if character at 'v' position is matching with 'getCharacter'
             * if matching then increament duplicateCount's value
             */
            if (str.charAt(v) == getCharacter) {
              duplicateCount++;
            }
          }
        }

        // if duplicates available of 'getCharacter' then display them
        if (duplicateCount != 0) {
          System.out.println(duplicateCount + " duplicate found of '" + getCharacter + "'");
        }
      }

    }
  }

  public static void main(String a[]) {

    // create an object of FindDuplicate class to call countDupChars() function in it
    FindDuplicate obj = new FindDuplicate();

    // print on screen
    System.out.println("String: learnoset");
    System.out.println("Duplicate Characters in learnoset");

    // calling function countDupChars() to check duplicate 
    obj.countDupChars("learnoset");

    // print on screen
    System.out.println("\nString: programming");
    System.out.println("Duplicate Characters in programming");

    // calling function countDupChars() to check duplicate 
    obj.countDupChars("programming");
  }
}