Java Program to Find Duplicate Characters in a String

This Java program is used to find duplicate characters in string.

Example:

public class DuplStr {
 public static void main(String argu[]) {

  String str = "w3schools";
  int cnt = 0;
  char[] inp = str.toCharArray();
  System.out.println("Duplicate Characters are:");
  for (int i = 0; i < str.length(); i++) {
   for (int j = i + 1; j < str.length(); j++) {
    if (inp[i] == inp[j]) {
     System.out.println(inp[j]);
     cnt++;
     break;
    }
   }
  }
 }
}

Program Output:

Duplicate Characters are: s o

Explanation:

Here in this program, a Java class name DuplStr is declared which is having the main() method. All Java program needs one main() function from where it starts executing program.  Inside the main(), the String type variable name str is declared and initialized with string w3schools. Next an integer type variable cnt is declared and initialized with value 0. This cnt will count the number of character-duplication found in the given string.

The statement: char [] inp = str.toCharArray(); is used to convert the given string to character array with the name inp using the predefined method toCharArray(). The System.out.println is used to display the message "Duplicate Characters are as given below:". Now the for loop is implemented which will iterate from zero till string length. Another nested for loop has to be implemented which will count from i+1 till length of string.

Inside this two nested structure for loops, you have to use an if condition which will check whether inp[i] is equal to inp[j] or not. If the condition becomes true prints inp[j] using System.out.println() with s single incrementation of variable cnt and then break statement will be encountered which will move the execution out of the loop.