String Programs in Java for Interview Best Practice
Here, we have collected top 15+ string programs in Java for interview with the best explanation.
These string programs in Java are very important for interview purpose and technical test.
These programming questions help you brush up your coding skills. So, you must practice all these string programs whole heartily.
Top String Programs in Java for Interview
Question 1: Write a Java program to count the total number of characters present in a string.
To count the number of characters present in the given string, we will iterate through the string and count the number of characters. Look at the program code below.
Program code:
public class CountCharacter {
public static void main(String[] args)
{
// Creating a string.
String string = "Every person loves his country";
// Set the count zero.
int count = 0;
// Counts each character except space.
for(int i = 0; i < string.length(); i++) {
if(string.charAt(i) != ' ')
count++;
}
// Prints the total number of characters present in the given string.
System.out.println("Total number of characters present in a string: " + count);
}
}
Output:
Total number of characters in a string: 26
In this example, we have used charAt() method of String class. Basically, the charAt() method returns the char value at the specified index. An index ranges from 0 to length() – 1. The first char value is at index 0, the next at index 1,and so on.
Question 2: Write Java program to count the number of vowels present in a string.
Program code:
import java.util.Scanner;
public class CountVowels {
public static void main(String[] args)
{
// Create a Scanner class object to accept input from keyword.
Scanner sc = new Scanner(System.in);
// Prompt the user to enter a string.
System.out.println("Enter a string: ");
String s = sc.nextLine();
// Call toCharArray() method of String class to convert string into char array.
char[ ] ch = s.toCharArray();
int vowel = 0;
for (int i = 0; i < s.length(); i++)
{
if(s.charAt(i)=='a' || s.charAt(i)=='A' || s.charAt(i)=='e' || s.charAt(i)=='E'
|| s.charAt(i)=='i' || s.charAt(i)=='I' || s.charAt(i)=='o' || s.charAt(i) == 'O'
|| s.charAt(i)=='u' || s.charAt(i) == 'U')
vowel++;
}
System.out.println("Number of vowels in the string: " + vowel);
}
}
Output:
Enter a string:
Union
Number of vowels in the string: 3
Algorithm:
a. Take a string input from user and store it in a variable called “s”.
b. Convert string to char array using toCharArray() method of String class.
c. Use for loop from i = 0 to i < s.length().
d. Check the following conditions using if statement: s.charAt(i)==’a’ or s.charAt(i)==’e’ or s.charAt(i)==’i’ or s.charAt(i)==’o’ or s.charAt(i)==’o’ to increment vowel++.
Question 3: Write a Java program to count the number of words present in a string.
There are three ways to count the number of words present in a string. Let’s see all three methods in the below program one by one.
Program code:
public class WordCount {
public static void main(String[] args)
{
// Calling static methods one by one.
m1();
m2();
m3();
}
// Method 1 to count the number of words present in a string.
private static void m1()
{
final String str = "I Love Java Programming!";
String[ ] strArray = str.split(" "); // Splitting the input string with space.
System.out.println("Number of words in a string = " + strArray.length);
}
// Method 2 to count the number of words present in a string.
private static void m2()
{
final String str = "Java Technology";
int count = 0;
for (String word : str.split(" "))
{
count++; // It will count the number of words present in the string array.
}
System.out.println("Number of words in a string = " + count);
}
// Method 3 to count the number of words present in a string.
private static void m3()
{
final String str = "Every people loves his country.";
int count = 1;
for (int i = 0; i < str.length() - 1; i++)
{
if ((str.charAt(i) == ' ') && (str.charAt(i + 1) != ' ')) {
count++;
}
}
System.out.println("Number of words in a string = " +count);
}
}
Output:
Number of words in a string = 4
Number of words in a string = 2
Number of words in a string = 5
Question 4: Let’s write a Java program to determine whether one string is the rotation of another string.
Program code:
public class StringRotation {
public static void main(String[] args)
{
String st1 = "abcde";
String st2 = "deabc";
if(st1.length() != st2.length())
{
System.out.println("Second string is not rotation of first string.");
}
else {
// Concatenate st1 with st1 and store it in st1.
st1 = st1.concat(st1);
// Check whether st2 is present in st1.
if(st1.indexOf(st2) != -1)
System.out.println("Second string is rotation of first string.");
else
System.out.println("Second string is not rotation of first string.");
}
}
}
Output:
Second string is rotation of first string.
Question 5: Write a Java program to find duplicate characters in a string.
Program code:
public class DuplicateCharacter {
public static void main(String[] args)
{
String str = "Great responsibility";
int count = 0;
// Converting given string into character array.
char[] ch = str.toCharArray();
System.out.println("Duplicate characters in the specified string: ");
// Counting each character present in a string.
for(int i = 0; i < ch.length; i++)
{
count = 1;
for(int j = i + 1; j < ch.length; j++)
{
if((ch[i] == ch[j]) && (ch[i] != ' '))
{
count++;
// Setting ch[j] to 0 to avoid printing visited character.
ch[j] = '0';
}
}
// If count is greater than 1 then consider character as duplicate.
if(count > 1 && ch[i] != '0')
System.out.println(ch[i]);
}
}
}
Output:
Duplicate characters in the specified string:
r
e
t
s
i
Question 6: Write a Java program to find the duplicate words in a string.
Program code:
public class DuplicateWords {
public static void main(String[] args)
{
String str = "Love life love his life his";
int count = 0;
// Converts string into lowercase.
str = str.toLowerCase();
// Now splits the string into words using split() method of String class.
String[] words = str.split(" ");
System.out.println("Duplicate words in the specified string: ");
// Counting each word present in a string.
for(int i = 0; i < words.length; i++)
{
count = 1;
for(int j = i + 1; j < words.length; j++)
{
if(words[i].equals(words[j])) {
count++;
// Setting words[j] to 0 to avoid printing visited word.
words[j] = "0";
}
}
// If count is greater than 1 then consider a word as duplicate.
if(count > 1 && words[i] != "0")
System.out.println(words[i]);
}
}
}
Output:
Duplicate words in the specified string:
love
life
his
Question 7: Write a Java program to find whether a string is palindrome.
Go to this tutorial for best explanation: String Palindrome in Java
Question 8: Write a program to check whether a number is palindrome.
Refer to this tutorial for best explanation: Palindrome number in Java
Question 9: Write a program to reverse a string in Java.
Go to this tutorial for best explanation: How to reverse a string in Java
Question 10: Write a program to separate individual characters from a string.
Program code:
public class IndividualCharacter {
public static void main(String[] args)
{
String str = "Technology";
// Prints individual characters from given string.
System.out.println("Individual characters from string: ");
// Iterate through string and print individual characters.
for(int i = 0; i < str.length(); i++)
{
System.out.print(str.charAt(i)+ " ");
}
}
}
Output:
Individual characters from string:
T e c h n o l o g y
Question 11: Write a Java program to sort an array of strings in alphabetical order.
Refer to this tutorial for best practice: How to Sort String in Java Alphabetically
Question 12: Write a Java program to determine the frequency of characters in the String.
Program code:
public class FrequencyOfCharacter {
public static void main(String[] args)
{
String str = "Welcome to Scientech Easy";
String lowerCase = str.toLowerCase();
char ch = 'e';
int frequency = 0;
for(int i = 0; i < lowerCase.length(); i++)
{
if(ch == lowerCase.charAt(i)) {
++frequency;
}
}
System.out.println("Frequency of character " + ch + " = " + frequency);
}
}
Output:
Frequency of character e = 5
