In this program, we will check for duplicate characters in a String and count the number of times each character is repeated using Java.

package com.topjavatutorial;

import java.util.HashMap;
import java.util.Map;

public class Demo {

  public static void main(String[] args) {
    String str = "topjavatutorial";
    int count = 0;
    char c;
    Map<Character, Integer> map = new HashMap<Character, Integer>();
    for (int i = 0; i < str.length(); i++) {
      c = str.charAt(i);
      if (map.containsKey(c)) {
        count = map.get(c);
        map.put(c, ++count);
      } else {
        map.put(c, 1);
      }
    }
    System.out.println(map);
  }
}

Output :

{p=1, a=3, r=1, t=3, u=1, v=1, i=1, j=1, l=1, o=2}

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