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Java Program to Count the Number of Repeated Characters in a String
This article is created to cover a program in Java that counts and prints the number of repeated or duplicate characters available in a given string. For example, if the given string is "Java Programming", then the output will be 4. Because the characters a, r, g, and m are available more than once.
Count the Number of Repeated Characters in a String: Basic Version
The question is: write a Java program to count the number of repeated characters in a string. The string must be received by the user at the runtime of the program. Here is its sample run:
import java.util.Scanner; public class CodesCracker { public static void main(String[] args) { String str; char ch; int strLen, i, count, j, k, repChars=0; Scanner s = new Scanner(System.in); System.out.print("Enter the String: "); str = s.nextLine(); strLen = str.length(); char[] arr = new char[strLen]; for(i=0; i<strLen; i++) arr[i] = str.charAt(i); for(i=0; i<strLen; i++) { ch = arr[i]; count = 0; for(j=(i+1); j<strLen; j++) { if(ch==arr[j]) { count++; for(k=j; k<(strLen-1); k++) arr[k] = arr[k+1]; strLen--; j--; } } if(count>0) repChars++; } System.out.println("\nTotal Number of Repeated Characters = " +repChars); } }
The snapshot given below shows the sample run of the above program with user input codescracker as a string to count and print the total number of duplicate characters available in it:
That is, the characters c, e, and r are the three characters available a repeated number of times. Therefore, the output was 3.
Count the Number of Repeated Characters in a String: Complete Version
The problem with the above program is that if the user enters a string containing white spaces, then white space duplication also gets counted. Therefore, let's modify the above program. Some other modifications are also done in the program given below:
import java.util.Scanner; public class CodesCracker { public static void main(String[] args) { int i, count, j, k, repChars=0; Scanner s = new Scanner(System.in); System.out.print("Enter the String: "); String str = s.nextLine(); str = str.replaceAll("\\s+", ""); str = str.toLowerCase(); int strLen = str.length(); char[] arr = new char[strLen]; for(i=0; i<strLen; i++) arr[i] = str.charAt(i); for(i=0; i<strLen; i++) { count = 0; for(j=(i+1); j<strLen; j++) { if(arr[i]==arr[j]) { count++; for(k=j; k<(strLen-1); k++) arr[k] = arr[k+1]; strLen--; j--; } } if(count>0) repChars++; } if(repChars==0) System.out.println("\nNo repeated character found."); else if(repChars==1) System.out.println("\nThere is only one repeated character found."); else System.out.println("\nThere are " +repChars+ " characters found in the String."); } }
Here is its sample run with user input "Java" as a string:
Here is another sample run with user input, "codescracker dot com"
In the above program, the statement:
str = str.replaceAll("\\s+", "");
is used to remove all white spaces (single space, multiple space (tabs)). And the following statement:
str = str.toLowerCase();
is used to convert the whole string to lowercase. Because the same character in uppercase and lowercase gets treated as a different character.
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