Suppose, we have given a string and asked us to dig out repeated characters and print over the screen. It is quite a tricky but its matter of fact how fast you build logic to find a solution.

Java program to find duplicate characters in a string using nested loops

Program:

public class RepeatedChar {
    public static void main(String[] args) {
        String str = "programmerbay";
        char[] ch1 = str.toLowerCase().toCharArray();
        int i, j, count;
        int len = ch1.length;
        System.out.println("Repeated characters in " + str);
        for (i = 0; i < len; i++) {
            count = 0;
            for (j = i + 1; j < len; j++) {
                if (ch1[i] == ch1[j]) {
                    count++;
                }
            }
            if (count == 1) System.out.print(ch1[i] + " ");
        }
    }
}

Output:

Repeated characters in programmerbay
r a m

Java program to find duplicate characters in a string using sort method and flags

Program :

public class DuplicateChar {
    public static void main(String[] args) {
        String str = "programmerbay";
        int flag = 0;
        char[] chrArr = str.toLowerCase().toCharArray();
        Arrays.sort(chrArr);
        System.out.println(" Duplicate Characters in the given String : ");
        for (int i = 0; i < chrArr.length - 1; i++) {
            if (chrArr[i] == chrArr[i + 1]) {
                if (flag == 0) {
                    System.out.println(chrArr[i]);
                }
                flag = 1;
            } else {
                flag = 0;
            }
        }
    }
}

Output:

 Duplicate Characters in the given String : 
a
m
r