Frequently Asked Java Programs 31 – Java Program to Find Common Characters in Two Given Strings

Hello Folks,

As part of Frequently Asked Java Programs In Interviews For Freshers And Experienced, in this post we will see a java program Find Common Characters in Two Given Strings.

String s1= “ABCDEF”

String s2= “DEFXYZ”

Output: DEF

This problem can be solved with or without using collection concepts in Java. I will explain both solutions here because in interview, you could be asked in any ways.

We need to iterate char by char a given string with smaller length.
Take the first char of a string say S1 and check if String say S2 contains that char. If yes, store in another resultant String. Repeat the same process for each char of S1.
After completion of iteration, resultant string will have common characters in both Strings.


package StringPrograms;

import java.util.Scanner;

public class CommonCharInTwoStrings {

        public static String commonChars(String str1, String str2) {
                StringBuilder commonChars = new StringBuilder();

                if (str1.length() > 0 & str2.length() > 0) {
                        // We should iterate the smallest string in length.
                        String toBeIterated = (str1.length() > str2.length() ? str2 : str1);
                        // Once string to be iterated is finalized, get string to be checked
                        String toBeChecked = toBeIterated.equals(str1) ? str2 : str1;
                        System.out.println("String to be iterated: " + toBeIterated);
                        System.out.println("String to be checked: " + toBeChecked);

                        // Iterating a string char by char
                        for (int i = 0; i < toBeIterated.length(); i++) {
                                // Check for common char
                                if (toBeChecked.contains(Character.toString(toBeIterated.charAt(i)))) {
                                        // If contains append it to resultant string
                                        commonChars.append(Character.toString(toBeIterated.charAt(i)));
                                }
                        }
                        return commonChars.toString();
                } else
                        return "";
        }

        public static void main(String[] args) {

                // User input for the string to know length
                Scanner sc = new Scanner(System.in);
                System.out.println("Please enter the first string");

                String string1 = sc.nextLine();

                System.out.println("Please enter the second string");

                String string2 = sc.nextLine();

                sc.close();

                System.out.println("Output is :" + commonChars(string1, string2));
        }

}

Output:-

Please enter the first string ABC Please enter the second string ABCDEF String to be iterated: ABC String to be checked: ABCDEF Output is :ABC======================================================Please enter the first string selenium Please enter the second string winium String to be iterated: winium String to be checked: selenium

Output is :inium

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