Top 25 Java String Programming Interview Questions and Answers

In this post, I have collected Java string programming and coding interview questions and answers that may help you to ace your next interview. These questions can be asked either to entry-level developers or experienced developers. Let's dive deep into the topic:

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Q1 How to reverse a string in Java? (with or without using built-in functions)

This question is perfect for entry-level Java developers. You can find the . I have also shared how to .

Q2 Write a Java program to find the first non-repeated character in the string?

I have already shared the easiest way to .

Q3 Write a Java program to count the number of words in a given string?

There are many ways to count the number of words in a given string. The simplest of them is given below:

public class CountNumberOfWords {
    public static void main(String args[]) {
        String input = "Alive is Awesome";
        String[] words = input.trim().split(" ");
        System.out.println(words.length);
    }
}

Q4 Write a Java program to count the number of occurrences of a given character in a given string?

The most common way of counting the number of occurrences of a given character in a given string is by using for loop. But in the below example, we are counting the number of occurrences of a given character in a given string without using for loop.

public class CountOccurrencesCharacter {
    public static void main(String args[]) {
        String input = "Alive is Awesome";
        char ch = 'i';
        int count = input.length() - input.replaceAll("i", "").length();
        System.out.println(count);
    }
}

Q5 Write a Java program to find the duplicate characters in a string?

This question can easily be solved using the HashSet class as shown below in the example. The interviewer may ask to solve this question without using Set/HashSet, so, be prepared for that also.

import java.util.HashSet;
import java.util.Set;

public class DuplicateCharacters {
    public static void main(String args[]) {
        String input = "Alive is Awesome";
        HashSet<Character> set = new HashSet<>();
        Set<Character> result = new HashSet<>();
        for(char ch : input.toCharArray())
        {
            if(!set.add(ch))
                result.add(ch);
        }
        System.out.println(result);       
    }
}

Q6 Write a Java program to count the number of occurrences of each character in a given string?

I have already shared the answer to this question in a separate post on .

Q7 Write a Java program to remove all whitespaces from a given string.

There are two ways to . One is using built-in Java methods. Another way is without using built-in methods. You can prepare for both ways.

Q8 Write a Java program to check if one given string is an anagram of another given string.

I have shared in a separate post to .

Q9 Write a Java program to check if one given string is the rotation of another given string?

I have already shared the code with examples to check if .

Q10 Write a Java program to find the count of characters that are not repeated in the string?

I have already shared the 3 ways to .

Q11 Write a Java program to print the last unique character of the string.

This question is quite similar to Q2, here, we are looking to write a .

Q12 Write a Java program to count the number of digits in a given string?

I have shared .

Q13 Check if a given string is an isogram or not.

This question is mainly asked to entry-level Java developers. I have already shared .

Q14 Write a Java program to get the first character of the string in Java

This question is mostly asked to entry-level Java developers. You can find the Java program to get the first character of the string in Java .

Q15 Write a Java program to shuffle a string in Java.

There are .

Q16 Write a Java program to count the number of commas in a string?

I have already shared .

Q17 Write a Java program to capitalize the first letter of a string in Java.

I have already shared the .

Q18 Write a Java program to find duplicate words in a string?

I shared 3 ways to .

Q19 Write a Java program to check if a string is a Pangram.

I already shared the .

Q20 Write a Java program to remove the first and last characters from the string.

You can find the .

Q21 Write a Java program to check if a string contains special characters.

I shared the .

Q22 Write a Java program to find all substrings of a string in Java.

You can find the solution of the .

Q23 Check if a string is an anagram in Java.

You can find the answer .

Q24 Write a Java program to determine if a string has all unique characters.

You can find the Java program to .

Q25 Write a Java program to find the permutation and combination of a given string.

This is one of the most important questions and should be on your to-do list before appearing for the interview. .

That's all for today. Please mention in the comments if you face any other string programming question in your interview which is not present in the above list.