Top 50+ Core Java Interview Questions

Q1. Find 6 mistakes in this Java code snippet?

package com.shubhamklogic.java-coding.interview.problems;

public class CheckIssues InProgram {

	static void Main(String[5] args) {
		String str = "xyz":
		System.out.println(s);
	}
}

Finding mistakes in a piece of code is a common core Java interview question pattern. In such problems, you’re given a piece of Java code with few syntactical issues, and you’ll have to find them. Here’s the code on Java-

Q2. Write a Java program to find Random number without using Math.random() method?

It’s an important Core Java Interview Question for all level Java developers. Let’s see how to use ThreadLocalRandom class to solve this Java interview question –

import java.util.concurrent.ThreadLocalRandom; 

public class RandomNumberProgram
{
    public static void main( String []arguments ) 
    { 
        // Default range is 0 to 999 to generate a list of Random numbers-
        int randomList1 = ThreadLocalRandom.current().nextInt(); 
        int randomList2 = ThreadLocalRandom.current().nextInt(); 
  
        // Printing random numbers-
        System.out.println("Random Integer : " + randomList1); 
        System.out.println("Random Integer : " + randomList2); 
  
        // The method nextDouble() would return Random values of double type-
        double randomDoubles1 = ThreadLocalRandom.current().nextDouble(); 
        double randomDoubles2 = ThreadLocalRandom.current().nextDouble(); 
  
        // Printing random values (of double type)
        System.out.println("Random Double : " + randomDoubles1); 
        System.out.println("Random Double : " + randomDoubles2); 
  
        // Method nextBoolean() would return boolean type random values-
        boolean randomBooleans1 = ThreadLocalRandom.current().nextBoolean(); 
        boolean randomBooleans2 = ThreadLocalRandom.current().nextBoolean(); 
  
        // Printing random Booleans 
        System.out.println("Random Boolean : " + randomBooleans1); 
        System.out.println("Random Boolean : " + randomBooleans2); 
    } 
}
/*                -: OUTPUT :-
    Random Integer : -2087413414
    Random Integer : 2010941294
    Random Double : 0.46600872829248874
    Random Double : 0.739558328779781
    Random Boolean : false
    Random Boolean : true                         */

Q3. Which condition would be executed in below Java code?

The below Java code snippet contains 2 conditions (with if blocks), and your task is to explain which one will be executed-

public class ProgramBySKL
{
    public static void main(String []arguments)
    {
        int num1 = 100;
        int num2 = 100;
        if(num1 == num2){      // Condition 1
            System.out.println("Numbers are Equal");
        }
        if(num1 =! num2){      // Condition 2
            System.out.println("Numbers are NOT Equal");
        }
    }
}

Q4. Find the output of the below Java program?

Try to find the output of this program-

public class FindOutputExample
{
    public static void main(String []arguments)
    {
        String website1 = "ShubhamKLogic.com";
        String website2 = "ShubhamKLogic.com";
        System.out.println("website1 == website2 :: " + website1 == website2 );
        // Output: website1 == website2 :: false
    }
}

Q5. What would be the size of HashSet object ‘theSet’?

Finding the size of theSet HashSet object-

import java.util.HashSet;
public class SizeOfHashSetExample
{
    public static void main(String []arguments)
    {
        HashSet theSet = new HashSet();
        for (short i = 0; i < 100; i++) {
            theSet.add(i);               // Adding the current number
            theSet.remove(i - 1);   // Removing the previous number
        }
        System.out.println( theSet.size() );
    }
}

Q6. How to remove Whitespaces from String using char Array?

To solve this question, we have to check for each character and remove it from the String-

package com.shubhamklogic.java.interview.questions;

public class RemoveWhiteSpacesExample
{
    public static void main(String []arguments)
    {
        System.out.println(whiteSpaceRemover( "ShubhamKLogic .com" ));
        System.out.println(whiteSpaceRemover( "Learn Programming With ShubhamKLogic.com" ));
    }

    // Method- responsible for removing white spaces...
    public static String whiteSpaceRemover( String theString )
    {
        StringBuilder theResult = new StringBuilder();
        
        char[] charArray = theString.toCharArray();      // Creating a char array.
        
        for(char c : charArray) {
            if (!Character.isWhitespace(c))     // Checking- if 'c' contains a whitespace or not!
                theResult.append(c);                  // If not, then append that character in result.
        }
        
        return theResult.toString();
    }
}

/*         -: OUTPUT :-
      ShubhamKLogic.com
      LearnProgrammingWithShubhamKLogic.com
*/

Q7. How to Sort an array in Java?

It’s mostly asked Core Java Interview Questions, which is also asked with different criterias using with or without. But, let’s see the fundamental solution-

package com.shubhamklogic.java.interview.questions;

import java.util.Arrays;

public class SortArrayExample {

    public static void main(String[] arguments) {

        int[] array = { 10, 30, 20, -11, -22, 44 }; // Creating an unsorted array

        Arrays.sort(array); // Sorting array- using utility class Arrays.sort() method,

        System.out.println(Arrays.toString(array));
    }
}

/*          -: OUTPUT :-
     [-22, -11, 10, 20, 30, 44]
*/

BTW, there are few popular Sorting algorithms as well, such as Bubble sort, Quick sort etc. You can Learn these Java Algorithms below.

Q8. How will you find Smallest and Largest Element in an Array?

Here’s an easy solution to find Smallest and Largest Element in an Array-

package com.shubhamklogic.java.interview.questions;

public class PA1Example {

    public static void main(String[] args) {

        int arr[] = new int[] { 30, 50, 70, 90, 10, 20, 40, 60, 180, 100 };

        int theSmallest = arr[0];                               // Step 1 : First element will be treated as the largest and smallest number (initially)
        int theLargest = arr[0];

        for (int i = 1; i < arr.length; i++) {                 // Step 2

            if (arr[i] > theLargest)                               // Step 3
                theLargest = arr[i];
            else if (arr[i] < theSmallest)                    // Step 4
                theSmallest = arr[i];

        }
        System.out.println("Smallest : " + theSmallest);            // Finally...
        System.out.println("Largest : " + theLargest);

    }
}

//  -: Output :-
     Smallest : 10
     Largest : 180

Q9. How to convert Java String into byte[]?

Here’s the easiest method to get a byte array from a String-

package com.shubhamklogic.java.interview.questions;

import java.util.Arrays;
import java.nio.charset.*;

public class StringToByteArraySolution {

    public static void main(String[] args) {

        String string = "ShubhamKLogic";
        byte[] bytes = string.getBytes();
        System.out.println("\nBytes( Simple Print)  = " + Arrays.toString(bytes));

        bytes = string.getBytes(Charset.forName("UTF-8"));
        System.out.println("\nBytes(Charset UTF-8)  = " + Arrays.toString(bytes));

        bytes = string.getBytes(StandardCharsets.UTF_8);                                                 // Platform Independent and Java 7+ only 
        System.out.println("\nBytes(Standerd UTF-8) = " + Arrays.toString(bytes));
    }
}

/*        -: Output :-

Bytes( Simple Print)  = [83, 104, 117, 98, 104, 97, 109, 75, 76, 111, 103, 105, 99]
Bytes(UTF-8)          = [83, 104, 117, 98, 104, 97, 109, 75, 76, 111, 103, 105, 99]
Bytes(Standerd UTF-8) = [83, 104, 117, 98, 104, 97, 109, 75, 76, 111, 103, 105, 99]     */

Q10. How many ways do you know to print a Java array?

First of all, It’s not a Java Interview Question, But I’ve added this question here, so that you can get to know all the different ways of print an array in one place.
Here’re a few of the easiest methods to print a 1-d and 2-d arrays:

package com.shubhamklogic.java.interview.questions;
import java.util.*;
import java.util.stream.*;

public class ArrayPrintingWays {

    public static void main(String[] args) {

        // Method 1: A Simple Array:
        String[] array = new String[] {
            "John",
            "Shubham",
            "Bob"
        };
        System.out.println("\n\nMethod 1) Array = " + Arrays.toString(array));


        // Method 2: A Nested Array:
        String[][] nestedArray = new String[][] {
            {
                "John",
                "Shubham"
            }, {
                "SKL",
                "Alex"
            }
        };

        // System.out.println(Arrays.toString(deepArray));      
        // This would NOT work! It will print just Memory Address
        // Output: [[Ljava.lang.String;@106d69c, [Ljava.lang.String;@52e922]

        System.out.println("\n\nMethod 2) NestedArray = " + Arrays.deepToString(nestedArray));


        // Method 3: Using Java Lambda Expression:
        System.out.print("\n\nMethod 3) Array = ");
        Arrays.asList(array).stream().forEach(
            element - > System.out.print(element + " ")
        );


        // Method 4: Using Java Stream API:
        System.out.println("\n\nMethod 4) Array = ");
        Stream.of(array).forEach(System.out::println);

    }
}

/*        -: Output :-
Method 1) Array = [John, Shubham, Bob]

Method 2) NestedArray = [[John, Shubham], [SKL, Alex]]

Method 3) Array = John  Shubham  Bob

Method 4) Array =
                       John
                       Shubham
                       Bob
*/

Q11. How to Implement Binary search of an array?

Binary Search in an important Java Interview Question. To search an element using binary search, the array elements must be in sorted order. Here’s the complete implementation of Binary Search in Java-

package com.shubhamklogic.java.interview.questions;

import java.util.*;

public class BinarySearchExample
{
	public static void main( String []args)
	{	      
                      // INDEX =     0    1    2    3   4    5   6
		int []theArray = { 10,70,40,50,70,80,90 };        // a sorted array...
		int theNumber = 70;                                          // the number to find...
		
		System.out.println( "Array : "+ Arrays.toString( theArray ) );
		
		int foundAt = binarySearch( theArray, 0, theArray.length-1, theNumber);
		
		if( foundAt < 0 )
			System.out.println( "Num "+ theNumber + " --> Not Found" );
		else
			System.out.println("Num "+ theNumber + " --> Found at index = "+ foundAt);
    }

    public static int binarySearch(int arr[], int low, int high, int target) 
    {
        int mid = (low + high) / 2;

        while (low <= high) 
        {
            if (arr[mid] < target)                                             // The 1st Case...
                low = mid + 1;
            else if (arr[mid] == target)                                  // The 2nd Case...
                return mid;
            else                                                                           // The 3rd Case...
                high = mid - 1;
            
            mid = (low + high) / 2;
        }
        if (low > high)                                                             // Final Case
        {
            return -1;
        }
        return -1;
    }
}
/*         -: OUTPUT :-
    Array : [10, 30, 40, 50, 70, 80, 90]
    Num 70 --> Found at index = 4
*/

Q12. How to reverse a String in Java?

It might be a little surprising, but the Java String class doesn’t have any particular reverse() method to reverse a String. Here is a complete program to reverse a String in Java-

package com.shubhamklogic.java.interview.questions;

public class StringReverseExample
{
    public static void main(String[] args) 
    {
		String theString = "ABCDEFG";
		System.out.println( theString + " <---> " + reverse(theString) );
    }

    public static String reverse(String theString) 
    {
        try{                                                                         // Checking for a valid input String...
            if (theString == null)
                throw new Exception("Invalid input");
        }catch( Exception e ){
            System.out.println(e.getMessage());
            return null;
        }

        StringBuilder reversedString = new StringBuilder();

	char[] chars = theString.toCharArray();        // Creating a char array to store string's characters...

	for (int k = chars.length - 1; k >= 0; k--)
		reversedString.append( chars[k] );

	return reversedString.toString();
    }
}
/*                -: OUTPUT :-
     ABCDEFG <----> GFEDCBA
*/

Q13. What is the output of the given Java code?

Here is a Java program, in which you have to tell- the output of the program:

package com.shubhamklogic.java.interview.questions;

public class GuessTheOutputSeries
{
    public static void main(String[] args) {
        foo(null);                                            // calling method foo()
    }
    public static void foo(Object o) {      // foo( takes Object )
        System.out.println("The Object method");
    }
    public static void foo(String s) {      // foo( takes String object )
        System.out.println("The String method");
    }
}
/*     -: OUTPUT :-
    The String method
*/

Q14. How many String objects are created by the below code?

It’s one of the tricky Core Java Interview Questions that confuse even experienced developers as well. Have a look at the Java code below, and try to find- How many String objects are created here.

package com.shubhamklogic.java.interview.questions;

public class CountObjectsExample
{
    public static void main(String[] args)
	{
		String s = new String("ShubhamKLogic (dot) com");
	}
}

Q15. Write a Java Program to check if a vowel is present in the string?

Here is a possible solution to this Core Java Interview Question (using something known as Regex / RegExp or) Regular Expression.

package com.shubhamklogic.java.interview.questions;

public class VowelCheckExample
{
       public static void main(String[] args) 
       {
		System.out.println( checkForVowels("ShubhamKLogic") );  
		System.out.println( checkForVowels("SKL") );
                System.out.println( checkForVowels("Java") );
	}
	public static boolean checkForVowels(String message) 
       {
        String vowelCheckerRegex = ".*[aeiou].*";
        return message.toLowerCase().matches( vowelCheckerRegex );
	}
}
/*  -: OUTPUT :-
             true
             false
             true          */

Q16. Write a Java program to Defang an (IPv4) IP Address.

A defanged version of an IP address replaces every period or dot “.” with “[.]”
Let’s say, you have an input IP address = “1.1.1.1” then output should be = “1[.]1[.]1[.]1”
Here’s a solution for this interview question-

package com.shubhamklogic.java.interview.questions;

public class IPAddressDefangingExample
{
    public static void main(String[] args) 
    {
        String ip = "255.255.255.1";
        ip=ip.replace(".","[.]");
        System.out.println( ip );
    }
}
/*     -: OUTPUT :-
    255[.]255[.]255[.]1
*/

Q17. How to convert a String into small letters without using string.toLowerCase()?

You can convert any String into small letters of English alphabet by implementing the below convertIntoLowerCase() method-

package com.shubhamklogic.java.interview.questions;

public class CustomLowerCaseExample
{
    public static void main(String[] args) 
    {
        System.out.println( convertIntoLowerCase("ShubhamKLogic.com") );
        System.out.println( convertIntoLowerCase("Learn To Code...") );
        System.out.println( convertIntoLowerCase("PROGRAMMING...") );
    }
    public static String convertIntoLowerCase(String theString) 
    {
        char[] arr = theString.toCharArray();
        for (int i = 0; i < arr.length; i++)
            if ('A' <= arr[i] && arr[i] <= 'Z')         // If the character is within the range of A - Z
                arr[i] = (char) (arr[i] - 'A' + 'a');   // Replace that character with it's small letter
        return new String(arr);
    }
}
/*     -: OUTPUT :-
    shubhamklogic.com
    learn to code...
    programming...
*/

Q18. Write a Java Program to Find Roman numbers of Given Integers?

It’s also one of the Tricky Java Interview Questions asked by different companies.

package com.shubhamklogic.java.interview.questions;

public class RomanNumberToIntegerExample
{
    public static void main(String[] args) 
    {
        System.out.println( convertIntToRoman(50) );
        System.out.println( convertIntToRoman(1000) );
        System.out.println( convertIntToRoman(777) );   
    }
    public static String convertIntToRoman(int num) 
    {
        String M[] = {"", "M", "MM", "MMM"};                                                                    // Range from 1000 to 3000
        String C[] = {"", "C", "CC", "CCC", "CD", "D", "DC", "DCC", "DCCC", "CM"};          // Range from 100 to 900
        String X[] = {"", "X", "XX", "XXX", "XL", "L", "LX", "LXX", "LXXX", "XC"};      // Range from 10 to 90
        String I[] = {"", "I", "II", "III", "IV", "V", "VI", "VII", "VIII", "IX"};                          // Range from 1 to 9
        return M[num/1000] + C[(num%1000)/100] + X[(num%100)/10] + I[num%10];           // Calculating & Returning Roman Numbers...
    }

}
/*  -: OUTPUT :-
           L
           M
           DCCLXXVII      */

Q19. How do I convert a String to an int in Java?

It’s one of the most important Java Coding Interview Questions, and you’ll use its solution probably more than a thousand times. Here, I’m going to show you 2 safe and secure ways of doing this-

package com.shubhamklogic.java.interview.questions;

public class StringToInt
{
    public static void main(String[] args) 
    {
        String strNum = "4455";

        Integer x = Integer.valueOf(strNum);   // Method - 1

        int y = Integer.parseInt(strNum);      // Method - 2

        System.out.println("1st Integer x = "+ x);
        System.out.println("2nd Integer y = "+ y);
    }
}
/*          -: OUTPUT :-
       1st Integer x =  4455
      2nd Integer y =  4455        */

Next Q20 to Q24 are based on Splitting a String with different delimiters-

split( String regularExpression )                     // returns String [ ]
split( String regularExpression, int limit )    // returns String [ ]

package com.shubhamklogic.java.interview.questions;

public class SplitStringByDotExample
{
    public static void main(String[] args) 
    {
        // String theFileNameWithExtension = "HelloPlanet.java";
        // String theFileName = theFileNameWithExtension.split(".")[0];   // Runtime Error
        // String theExtension = theFileNameWithExtension.split(".")[1];   // Runtime Error


        // The correct way to split the file name and extension...

        String theFileNameWithExtension = "HelloEarth.java";
        String theFileName = theFileNameWithExtension.split("\\.")[0];     // placed 2 backslashes \\ before the . dot
        String theExtension = theFileNameWithExtension.split("\\.")[1];

        System.out.println("File Name With Extension : "+ theFileNameWithExtension);
        System.out.println("File Name                : "+ theFileName);
        System.out.println("Extension                : "+ theExtension);
    }
}
/*  OUTPUT: 
      ------------
     File Name With Extension : HelloEarth.java
     File Name                : HelloEarth
     Extension                : java                                    */

package com.shubhamklogic.java.interview.questions;

import java.util.Arrays;

public class SplitByPipes {

    public static void main(String[] arguments) {

        String stringWithPipes = "12345|abcd|123numberText";
        String[] splittedParts = stringWithPipes.split("\\|");        // LITERAL pipe | symbol
        System.out.println(Arrays.toString(splittedParts));

        /*
           -: Output :- 
                12345,
                abcd,
                123numberText
        */
    }
}

package com.shubhamklogic.java.interview.questions;

import java.util.Arrays;

public class LimitedSplitExample {

    public static void main(String[] arguments) {

        String stringPhNum = "101-2001-300003";                      // String containing dash or hyphens (-) 
        String[] fullParts = stringPhNum.split("-");                      // Splitting string by dash (-) 
        String[] onlyLimitedParts = stringPhNum.split("-", 2); // Limiting the results to split till maximum 2 values

        System.out.println("All the Parts    : " + Arrays.toString(fullParts));
        System.out.println("Limited Parts    : " + Arrays.toString(onlyLimitedParts));
    }
}
/*  -: Output :-
         All the Parts      : [101, 2001, 300003]
         Limited Parts   : [101, 2001-300003]
*/

package com.shubhamklogic.java.interview.questions;

import java.util.Arrays;

public class SplitByHyphenExample {
    
    public static void main(String[] arguments) {
        
        String strPhoneNo = "ABC-1011-FGHI-20222";      // A string containing dash or hyphen (-)
        String[] partsPhoneNum = strPhoneNo.split("-"); // Splitting the string by - hyphen (or dash)

        System.out.println(Arrays.toString(partsPhoneNum));
    }
}
/*             -: Output :-
    [ABC, 1011, FGHI, 20222]     */

Q24. How to split a string in Java using Comma (,)?

Here is how to split a string using a comma (,) as a delimiter –

package com.shubhamklogic.java.interview.questions;

import java.util.Arrays;

public class SecondSplitExample
{
    public static void main( String[] arguments)
    {
        String allBooks = "Java,Data structure,C++,Python";         // A string containing comma (,) 
        String[] theArrayOfBooks = allBooks.split(",");             // Splitting the string by , comma
        System.out.println(Arrays.toString( theArrayOfBooks ));
    }
}
/*          -: Output :-
Index: 0       1           2        3              4
    [Java, Data structure, C++, Python]
*/

Q25. How to Remove Leading and Trailing whitespaces from a String?

Here is how you can remove those whitespace in Java-

package com.shubhamklogic.java.interview.questions;

public class RemoveWhitespacesProgram {

    public static void main(String[] arguments) {

        String websiteName = "  ShubhamKLogic    com  \t";
        websiteName = websiteName.trim();                          // Prints: "ShubhamKLogic    com"
        System.out.println(websiteName);
    }
}

Q26. How to remove all occurrences of a given Character from a String?

You might be surprised after knowing that, the java.lang.String class doesn’t have any direct method to remove a particular character from it. Here is a possible solution to achieving it-

package com.shubhamklogic.java.interview.questions;

public class RemoveCharOccuranceExmple{

    public static void main( String[] arguments){

        String websiteForCoders = "ShubhamKLogic.com";
		
        websiteForCoders = websiteForCoders.replace("o", "");    // Removing 'o' from string

        System.out.println( websiteForCoders );

    }
}

/*  -: Output :-
    ShubhamKLgic.com  */

Q27. How to get unique characters and their count in a String?

Here is a possible solution by using HashMap Data Structure.
In Java Collection API, there is a class HashMap, which doesn’t accept duplicate objects (in this case- Character objects), and we will take advantage of it.

package com.shubhamklogic.java.interview.questions;

import java.util.Map;
import java.util.HashMap;

public class GetUniqueCharExample {

    public static void main(String[] arguments) {

        String msg = "GoodJavaProgramming";

        char[] allChars = msg.toCharArray();

        Map < Character, Integer > charCounterMap = new HashMap < > ();

        for (char c: allChars) {

            if (charCounterMap.containsKey(c))
                charCounterMap.put(c, charCounterMap.get(c) + 1);

            else
                charCounterMap.put(c, 1);

        }

        System.out.println("All Unique Characters of \"" + msg + "\": " + charCounterMap);

    }
}

/*                          -: Output :-
All Unique Characters of "GoodJavaProgramming":
{P=1, a=3, r=2, d=1, v=1, G=1, g=2, i=1, J=1, m=2, n=1, o=3}       */

Q28. How to check if a String is Numeric in Java?

We can solve this Java Programming Interview Question by using Wrapper Class method – parseXXYYZZ(). In this method, just replace ‘XXYYZZ‘ with Int, Float or Double. Here is a Complete soution of it:

package com.shubhamklogic.java.interview.questions;

public class CheckNumericExample {

    public static void main(String[] arguments) {

        String age1 = "22";
        String age2 = "22 years";

        if (isNumeric(age1))
            System.out.println("age1 is Numeric");          // if block will EXECUTE...
        else
            System.out.println("age1 is NOT Numeric");

        if (isNumeric(age2))
            System.out.println("age2 is Numeric");
        else
            System.out.println("age2 is NOT Numeric"); // else block will EXECUTE...

    }
    public static boolean isNumeric(String str) {

        try {
            Double.parseDouble(str);                                  // Checking for Number, If successfully parsed, return true...
            return true;
        } catch (NumberFormatException e) {
            return false;
        }
    }
}

/*        -: Output :-
        age1 is Numeric
        age2 is NOT Numeric         */

Q29. How to convert a Java string into a Date object?

Suppoach you have a date as string in “MMMM DD YYYY” format and you want complete information about that particular date, here is a possible solution for this Java Interview Question-

package com.shubhamklogic.java.interview.questions;

import java.util.Date;
import java.util.Locale;
import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;

public class ConvertStringToDate {

    public static void main(String[] arguments) throws ParseException {

        String birthdayStr = "March 27, 1997";
        DateFormat theFormat = new SimpleDateFormat("MMMM d, yyyy", Locale.ENGLISH);

        Date date = theFormat.parse(birthdayStr);
        System.out.println("\"" + birthdayStr + "\" Converted into ==> \n" + date);
    }
}

/*        -: Output :-
"March 27, 1997" Converted into ==>
Thu Mar 27 00:00:00 IST 1997            */

Q30. How to remove last character of String without replace() method?

It’s a basic level Java Interview Question, and you might already know how to solve it. Here is a possible solution-

package com.shubhamklogic.java.interview.questions;

public class RemoveLastCharExample {

    public static void main(String[] arguments) {

        String siteWithExtraDot = "Java <=> ShubhamKLogic.com.";

        siteWithExtraDot = removeLastChar(siteWithExtraDot);

        System.out.println(siteWithExtraDot);
    }

    public static String removeLastChar(String str) {

        if (str == null || str.length() == 0) {
            return str;
        }
        return str.substring(0, str.length() - 1);

    }
}

/*        -: Output :-
Java <=> ShubhamKLogic.com        */

Q31. How to capitalize first character of each word in String?

At first look, such Core Java Interview Questions may seem too easy, but It’s NOT.
There are so many test cases tied with this question, and you will have to pay attention a bit more deeply on all of them. BTW, there’s no direct method provided by Java Team to solve such questions, but no worry, here’s an efficient solution, that works absolutely fine for almost all of the cases.

package com.shubhamklogic.java.interview.questions;

public class CapitalizeRequiredWordsSolution {

    public static void main(String[] arguments) {

        String[] messages = { // Sample sentences...

            // Test Case 1: A SIMPLE USAGE
            "cApItAlIzE my string after WHITE SPACES",

            // Test Case 2: WITH CUSTOM-DELIMITER USAGE
            "capitalize my string AFTER SPACES, BEFORE'APEX, and #AFTER AND BEFORE# NUMBER SIGN (#)",

            // Test Case 3: WITH MULTIPLE CUSTOM-DELIMITER
            "capitalize my string ONLY before'and''after'''APEX"

            // (SKIPPING REST OF THE CASES UPTO YOU...)
        };

        for (int i = 0; i < messages.length; i++) {
            String capitalizedMsg = capitalizeAllWords(messages[i]); // Calling custom build method...
            System.out.println("Before==>\"" + messages[i] + "\"");
            System.out.println("After ==>\"" + capitalizedMsg + "\"");
        }
    }
    public static String capitalizeAllWords(String giantString) {

        char[] allChars = giantString.toLowerCase().toCharArray(); // Point 1
        boolean found = false;

        for (int i = 0; i < allChars.length; i++) {                                      // Point 2

            if ( !found && Character.isLetter(allChars[i]) ) {                    // Point 3

                allChars[i] = Character.toUpperCase(allChars[i]);
                found = true;

            } else if (Character.isWhitespace(allChars[i]) || allChars[i] == '.' || allChars[i] == '\'') { // You can add any other Separator or Character here...
                found = false;
            }
        }
        return giantString.valueOf(allChars);                                            // Final Point
    }
}

/*                -: Output :-
Before==>"cApItAlIzE my string after WHITE SPACES"
After ==>"Capitalize My String After White Spaces"

Before==>"capitalize my string AFTER SPACES, BEFORE'APEX, and #AFTER AND BEFORE# NUMBER SIGN (#)"
After ==>"Capitalize My String After Spaces, Before'Apex, And #After And Before# Number Sign (#)"

Before==>"capitalize my string ONLY before'and''after'''APEX"
After ==>"Capitalize My String Only Before'And''After'''Apex"               */

Q32. How to check if two Strings are Anagrams in Java?

By the way, If you are unaware of the term Anagram, here is that-
Anagrams mean- Two Strings having the same characters in a different order.
Few Example: “Listen” = “Silent”
“The eyes” = “They see”
Here’s the easiest way to check if two Strings are Anagrams or not-

package com.shubhamklogic.java.interview.questions;

public class AnagramSolution {

    public static void main(String[] args) {

        String word1 = "shubhamklogic.com";
        String word2 = "com.logicShubhamk";

        System.out.println(word1 + " AND " + word2 + " ARE ANAGRAMS ? :: " + isAnagram(word1, word2));

    }

    public static boolean isAnagram(String word1, String word2) {

        if (word1.length() != word2.length())
            return false;

        for (int i = 0; i < word1.length(); i++) {

            char ch1 = word1.toLowerCase().charAt(i);
            int index = word2.toLowerCase().indexOf(ch1);

            // If index of any character is -1, then the two given strings are not anagrams
            // If index of character is not equal to -1, then remove the chacter from the
            // String and check till the end...

            if (index != -1) {
                word2 = word2.substring(0, index) +
                    word2.substring(index + 1, word2.length());
            } else
                return false;
        }
        return word2.isEmpty();
    }
}

/*                    -: Output :-
    shubhamklogic.com AND com.logicshubhamk ARE ANAGRAMS ? :: true    */

Q33. How will you find all substrings of a String?

Here’s the easiest method to list down all substrings of a String-

package com.shubhamklogic.java.interview.questions;

public class AllSubstringSolution {

    public static void main(String[] args) {

        String word = "SKL";
        System.out.println("All possible substrings of word SKL are: ");

        for (int i = 0; i < word.length(); i++) {

            for (int j = i + 1; j <= word.length(); j++) {
                System.out.println(word.substring(i, j));

            }
        }
    }
}

/*        -: Output :-
All possible substrings of word SKL are: 
S
SK
SKL
K
KL
L
*/

Q34. How to remove duplicates from ArrayList in Java?

It’s one of the most Important Core Java Interview based on Collections API, and a number of Java Developers face trouble when solving it. Here is it’s one liner solution-

package com.shubhamklogic.java.interview.questions;
import java.util.*;
public class RemoveDuplicatesSolution {

    public static void main(String[] arguments) {

        List < String > list = new ArrayList < String > ();
        list.add("Practice");
        list.add("Java Interview");
        list.add("Java Interview");
        list.add("@ShubhamKLogic.com");
        list.add("@ShubhamKLogic.com");
        list.add("@ShubhamKLogic.com");

        System.out.println("========= With Duplicate Element =======\n");
        System.out.println(list);

        list = new ArrayList < String > (new LinkedHashSet < String > (list));              // One line Solution...

        System.out.println("=========== Without Duplicates ===========\n");
        System.out.println(list);
    }
}

/*        -: Output :-

========= With Duplicate Element =======

[Practice, Java Interview, Java Interview, @ShubhamKLogic.com, @ShubhamKLogic.com, @ShubhamKLogic.com]

=========== Without Duplicates ===========

[Practice, Java Interview, @ShubhamKLogic.com]          */

Q35. How to Revese a Linked List?

Here’s again a one-liner solution to reverse any linked list:

package com.shubhamklogic.java.interview.questions;

class Node                                                             // Creating a class for nodes of Linked List...
{
    int data;
    Node next;

    Node(int data, Node next) {
        this.data = data;
        this.next = next;
    }
}

public class ReverseLinkedListSolution {

    public static void printList(Node head) // Helper method to print nodes' values of given linked list
    {
        Node ptr = head;
        while (ptr != null) {
            System.out.println(ptr.data + " -> ");
            ptr = ptr.next;
        }

        System.out.println("null");
    }

    public static Node reverse(Node head) // Reverse method for List
    {
        Node prev = null;
        Node current = head;


        while (current != null)                            // Traversing the list
        {

            Node next = current.next;                   // Focus: store the next node

            current.next = prev;                             // Manage the current node

            prev = current;
            current = next;
        }
        return prev;                                              // Fixing the head to point to the new front
    }

    public static void main(String[] args) // Iterative method to reverse a linked list
    {
        int[] keys = { 1,  2, 3, 4, 5, 6 }; // Input keys

        Node head = null;
        for (int i = keys.length - 1; i >= 0; i--) {
            head = new Node(keys[i], head);
        }
        System.out.println("\n===== Before =====");
        printList(head);
        head = reverse(head);
        System.out.println("\n===== After ======");
        printList(head);
    }
}

/*    -: OUTPUT :-

===== Before =====
1 -> 2 -> 3 -> 4 -> 5 -> 6 -> null

===== After ======
6 -> 5 -> 4 -> 3 -> 2 -> 1 -> null
*/

Q36. How to merge two lists in Java?

Here is a possible solution of this Java Interview Questions-

package com.shubhamklogic.java.interview.questions;

import java.util.*;
public class MergeListsSolution {

    public static void main(String[] arguments) {

        List < String > listA = new ArrayList < > ();
        listA.add("10");
        listA.add("20");
        List < String > listB = new ArrayList < > ();
        listB.add("40");

        List < String > mergedList = new ArrayList < > (listA);
        mergedList.addAll(listB);
        System.out.println(mergedList);
    }

}

/*   -: Output :-
    [10, 20, 40]
*/

Q37. How to Sort HashMap by values?

It’s also, one of the mostly asked Core Java Interview Questions. Here is one of its possible solution using Java LinkedHashMap class-

package com.shubhamklogic.java.interview.questions;

import java.util.*;

public class SortHashMapSolution {

    public static void main(String[] arguments) {

        Map < String, Integer > persons = new HashMap < > ();

        persons.put("David", 95);
        persons.put("SKL", 22);
        persons.put("Mary", 97);
        persons.put("Lisa", 78);
        persons.put("Dino", 65);

        System.out.println("====== BEFORE: UnSorted ======");
        System.out.println(persons);

        persons = sortMapByValue(persons);

        System.out.println("====== AFTER : Sorted =======");
        System.out.println(persons);
    }

    private static Map < String, Integer > sortMapByValue(Map < String, Integer > persons) {

        Map < String, Integer > sortedMapByValue = new LinkedHashMap < > ();

        // Getting the Map.EntrySet object...
        Set < Map.Entry < String, Integer >> entrySet = persons.entrySet();

        // Creating the List of Map.EntrySet
        List < Map.Entry < String, Integer >> entryList = new ArrayList < > (entrySet);

        // sort the list by value
        entryList.sort((x, y) - > x.getValue().compareTo(y.getValue()));

        // Populating the map with sorted values
        for (Map.Entry < String, Integer > e: entryList)
            sortedMapByValue.put(e.getKey(), e.getValue());

        return sortedMapByValue;
    }

}

/*                 -: Output :-

====== BEFORE: UnSorted ======
{SKL=22, Dino=65, David=95, Mary=97, Lisa=78}

====== AFTER : Sorted =======
{SKL=22, Dino=65, Lisa=78, David=95, Mary=97}		*/

Q38. How to get distinct characters and their count in a String?

To solve this question, we can take advantage of Map class in Java Collections. Here is its solution-

package com.shubhamklogic.java.interview.questions;

import java.util.*;

public class DistinctCharAndCountSolution {

    public static void main(String[] arguments) {

        String string = "ShubhamKLogic.com.com.SKL";

        char[] allChars = string.toCharArray();

        Map < Character, Integer > charsCount = new HashMap < > ();

        for (char ch: allChars) {
            if (charsCount.containsKey(ch)) {
                charsCount.put(ch, charsCount.get(ch) + 1);
            } else
                charsCount.put(ch, 1);
        }

        System.out.println("====== Count of Individual Characters ======");
        System.out.println(charsCount);

    }
}

/*                           -: Output :-
====== Count of Individual Characters ======
{a=1, b=1, c=3, g=1, h=2, i=1, K=2, L=2, m=3, .=3, o=3, S=2, u=1}  */

Q39. How to print odd-even numbers using threads in Java?

It’s one of the important Core Java Interview Questions for Experienced developers as well. In this problem, You are given two threads and you need to print odd numbers using one thread while even numbers using another thread.
You need to print odd-even numbers in natural order up to MAX_VALUE.

package com.shubhamklogic.java.interview.questions;

public class OddEvenWithThread {

    boolean odd;
    int count = 1;
    int MAX_VALUE = 10;

    public void printOdd() {

        synchronized(this) {

            while (count < MAX_VALUE) {

                while (!odd) {

                    try {

                        wait();

                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }

                System.out.println("Odd Thread :" + count);

                count++;
                odd = false;
                notify();                                           // Notifying the other thread...I'm done!
            }
        }
    }

    public void printEven() {

        try {

            Thread.sleep(1000);

        } catch (InterruptedException e1) {
            e1.printStackTrace();
        }

        synchronized(this) {

            while (count < MAX_VALUE) {

                while (odd) {

                    try {

                        wait();

                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }

                }

                System.out.println("Even thread :" + count);

                count++;
                odd = true;
                notify();                                          // Notifying the other thread...I'm done!
            }
        }
    }

    public static void main(String[] args) {

        OddEvenWithThread oep = new OddEvenWithThread(); // Creating the Object
        oep.odd = true;

        Thread td1 = new Thread(new Runnable() { // Creating 1st thread

            @Override
            public void run() {
                oep.printEven();
            }
        });

        Thread td2 = new Thread(new Runnable() { // Creating 2nd thread

            @Override
            public void run() {
                oep.printOdd();
            }
        });

        td1.start(); // 1st thread is ready to run()
        td2.start(); // 2nd thread is ready to run()

        try {

            td1.join();
            td2.join();

        } catch (InterruptedException e) {
            e.printStackTrace();
        }
    }
}
/*  -: Output :-

Odd Thread : 1
Even thread :2
Odd Thread : 3
Even thread :4
Odd Thread : 5
Even thread :6
Odd Thread : 7
Even thread :8
Odd Thread : 9
Even thread :10
*/

Q40. How do you kill a Thread in Java?

You may be surprised after knowing, Java threads can not be killed explicitly, but the stopping of a thread is done in an indirect and cooperative way.
The thread is asked to stop their remaining execution and the thread can then shutdown gracefully.
However, a volatile boolean field is used, and the thread periodically checks and terminates when it’s updated with the corresponding value. Here is the solution of terminating a thread whenever desired:

public void run() {
    try {
        while (!interrupted()) {
            // ...
        }
    } catch (InterruptedException exception)
    /* Exit code for thread */
}
}

public void cancel() {
    interrupt();
}

Q41. How to pass a parameter to a Java Thread?

It is possible to pass a parameter to a Java Thread and for doing so, you can pass the parameter in the constructor of the Runnable object. Here is the solution for you-

public class TheRunnable implements Runnable {

    public TheRunnable(Object theParameter) {       // Thread's Constructor with parameters...
           // Use the parameter...
    }

    public void run() {}
}

// and invoke it thus:

Runnable r1 = new TheRunnable(yourParameter);  // passed the parameter in thread 'r1'

new Thread(r).start();

Q42. How to create Floyd Triangle Pattern in Java?

It’s a Star-Pattern based problem and mostly asked Core Java Interview Questions for Freshers. Floyd Triangle Pattern is one of the common Pattern problems, and here’s its simplest solution-

/*  Floyd Triangle Pattern:

1
2 3
4 5 6
7 8 9 10
11 12 13 14 15

*/

package com.shubhamklogic.java.interview.questions;

public class FloydTriangleSolution {

    public static void main(String[] arguments) {

        printFloyydTrianglePattern();

    }
    public static void printFloyydTrianglePattern() {

        int k = 1;
        for (int i = 1; i <= 5; i++) {
            for (int j = 1; j <= 9; j++) {

                if (j % 2 != 0 && j < i * 2)
                    System.out.print(k++);
                else
                    System.out.print(" ");
            }
            System.out.print("\n");                                         // Put a new line when required numbers are print in each row...
        }
    }
}

Q43. Write a program to print the below pattern?

Here is the solution of it-

/*     Pattern:

        ABCDEFG
        ABC EFG
        AB   FG
        A     G
*/
package com.shubhamklogic.java.interview.questions;

public class PatternSolution {

    public static void main(String[] arguments) {

        printPattern();

    }
    public static void printPattern() {

        char k;
        for (int i = 1; i <= 4; i++) {
            k = 'A';
            for (int j = 1; j <= 7; j++) {
                if (j >= 6 - i && j <= 2 + i) {
                    System.out.print(" ");
                } else
                    System.out.print(k);
                k++;
            }
            System.out.print("\n");
        }
    }
}

Q44. Write a program to print the below pattern?

Here is the solution-

/* Pattern:

   1
  A B
 1 2 3
A B C D

*/

package com.shubhamklogic.java.interview.questions;

public class PatternSolution {

    public static void main(String[] arguments) {

        printPattern();
        // char ch = 49;
        // System.out.print(ch);

    }
    public static void printPattern() {

        int k = 0;
        for (int i = 1; i <= 4; i++) {
            if (i % 2 == 0)
                k = 65; // 65 is the ASCII value of character 'A'
            else
                k = 49; // 49 is the ASCII value of character '1'

            for (int j = 1; j <= 7; j++) {
                if (i % 2 == 0) {
                    if (j >= 5 - i && j <= 3 + i && j % 2 != 0) {
                        System.out.print((char) k);
                        k++;
                    } else
                        System.out.print(" ");
                } else {
                    if (j >= 5 - i && j <= 3 + i && j % 2 == 0) {
                        System.out.print((char) k);
                        k++;
                    } else
                        System.out.print(" ");
                }
            }
            System.out.print("\n");
        }
    }
}

Q45. Write a program to print the below pattern?

Here is the solution-

/* Pattern:

    A
   CB
  FED
 JIHG
ONMLK

*/
package com.shubhamklogic.java.interview.questions;

public class PatternSolution {

    public static void main(String[] arguments) {

        printPattern();

    }
    public static void printPattern() {

        /*	Steps of Logical Implementation of this Pattern Program:

        		Pattern    Hint	Initial Value
        		     A	     1	        1			 (THEN Increment till the end of Columns to print...)
        		   CB	   23        2
        		  FED	  345	3
          		 JIHG    6789       6
        		ONMLK	 ...	       10
        */

        int k = 64, m = 0, p;                           // Initially...
        for (int i = 1; i <= 5; i++) {

            m++;
            k = k + m;
            p = k;                                                 // Get Initial Value to Print on Each Line...

            for (int j = 1; j <= 5; j++) {
                if (j >= 6 - i) {                              // Range of All Columns to print...
                    System.out.print((char) p--);
                } else
                    System.out.print(" ");
            }
            System.out.print("\n");
        }
    }
}

Q46. Write a program to print the below pattern?

Here is the solution of the pattern-

/* Pattern

*********
 *******
  *****
   ***
    *
*/
package com.shubhamklogic.java.interview.questions;

public class PatternSolution {

    public static void main(String[] arguments) {

        printPattern();

    }
    public static void printPattern() {
        /* Steps to Logically Implement this Pattern Program: 

                           Output
                i 	123456789	    j					j
        -------------------------------------------------------------------
        step 1	*********	1 to 9             	j >= i  &&  j <= 10-i
        step 2	 *******	       2 to 8   	        j >= i  &&  j <= 10-i
        step 3	  *****	       3 to 7	   	j >= i  &&  j <= 10-i
        step 4	   ***	      4 to 6		j >= i  &&  j <= 10-i
        step 5	     *	              5 to 5	   	j >= i  &&  j <= 10-i

        */
        for (int i = 1; i <= 5; i++) {
            for (int j = 1; j <= 9; j++) {

                if (j >= i && j <= 10 - i)         // Check, whether to print * or space ( )
                    System.out.print("*");
                else
                    System.out.print(" ");
            }
            System.out.print("\n");
        }
    }
}

Q47. How to check Armstrong number using Java?

If you’re unaware of Armstrong numbers, Here’s what exactly Armstrong Number is-
An Armstrong number is a number that is equal to the sum of cubes of its digits.
For example: 153,
Explaination: 153 = [(1x1x1)+(5x5x5)+(3x3x3)],
Here is a Java program to check Armstrong number:

package com.shubhamklogic.java.interview.questions;

public class ArmstrongNumberSolution {

    public static void main(String[] args) {

        System.out.println(" Check: 153 is Armstrong number: " + checkArmStrongNumber(153));
        System.out.println(" Check: 200 is Armstrong number: " + checkArmStrongNumber(200));
        System.out.println(" Check: 407 is Armstrong number: " + checkArmStrongNumber(407));
    }
    public static boolean checkArmStrongNumber(int checkingNumber) {
        int sum = 0;
        int originalNumber = checkingNumber;
        while (checkingNumber != 0) {

            int remainder = checkingNumber % 10;
            sum = sum + remainder * remainder * remainder;
            checkingNumber = checkingNumber / 10;
        }
        if (originalNumber == sum) {
            return true;
        }
        return false;
    }
}
/*                      -: Output :-
 Check: 153 is Armstrong number: true
 Check: 200 is Armstrong number: false
 Check: 407 is Armstrong number: true
*/

Q48. Write Java program to check whether a String is a Palindrome?

If you’re unaware of Palindrome, A palindrome is a String that remains the same even after reverse.
For example: 545, 151, 34543, MADAM, POP etc. are the Palindromes.

package com.shubhamklogic.java.interview.questions;

public class PalindromeSolution {

    public static void main(String[] arguments) {

        String string1 = "MADAM";
        String string2 = "SIR";

        checkPalindrome(string1);
        checkPalindrome(string2);
    }

    public static void checkPalindrome(String string) {

        String reverse = "";
        for (int i = string.length() - 1; i >= 0; i--)
            reverse = reverse + string.charAt(i);

        if (string.equals(reverse))
            System.out.println(string + " ==> Palindrome");
        else
            System.out.println(string + " ==> Not palindrome");

    }
}
/*  =: OUTPUT :=
MADAM ==> Palindrome
SIR ==> Not palindrome
*/

Q49. How to Generate a Fibonacci Series in Java?

Generating Fibonacci series is one of the mostly asked Core Java Interview Questions for Freshers. In this problem, you need to generate a list of numbers in which every next number is the calculated Number of previous two numbers.
Explaining Example:
0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55 etc.
In Fibonacci series, the First two digits (0 and 1) are initiators. Next numbers will be calculated Number like this-
Num=Pre+Next
1  = 0 + 1
2  = 1 + 1
3  = 1 + 2
5  = 2 + 3
…
There are multiple ways to generate a Fibonacci Series, here I’m sharing an Iterative Method-

package com.shubhamklogic.java.interview.questions;

public class FibonacciSeriesSolution {

    public static void main(String[] arguments) {

        int prev = 0, next = 1;                                     // First two number of Fibonacci Series

        System.out.print(prev + " " + next);            // Print first two elements

        int range = 10;                                                 // Range of Numbers to be printed
        int calculatedNumber = 0;

        for (int i = 2; i < range; i++) {

            calculatedNumber = prev + next;
            System.out.print(" " + calculatedNumber);

            prev = next;                                                   // Update the numbers prev and next
            next = calculatedNumber;
        }
    }
}
/*
     -:OUTPUT:-
0 1 1 2 3 5 8 13 21 34
*/

Q50. How to Sort an Array using Bubble Sort?

Sorting algorithms are favorite Interview Questions of Companies like- Amazon, Google, Uber, or others.
Bubble Sort is used to sort elements of an array. In this sorting algorithm, each element of the array is compared with its adjacent element. A list with N elements requires N-1 rounds or passes for complete sorting.

package com.shubhamklogic.java.interview.questions;

public class BubbleSortSolution {

    public static void main(String[] args) {

        // Un-Sorted Array...
        int[] arr = new int[] { 30, 20, 10, 70, 60, 80, 50, 40 };

        System.out.println("\n====== Before Sorting ======");
        for (int n: arr)
            System.out.print(" " + n);

        performBubbleSort(arr);                    // Bubble Sort called...

        System.out.print("\n======= After Sorting ======");
        for (int n: arr)
            System.out.print(" " + n);

        System.out.print("\n======= Already Sorted ======");
        performBubbleSort(arr);                                                     // Bubble Sort called...

    }
    public static void performBubbleSort(int[] arr) {

        int swaps = 0;
        for (int k = 1; k < arr.length; k++) {

            int flag = 0;                                                                     // Flag will check, if further sorting is necessary or not!
            for (int i = 0; i < arr.length - k; i++) {

                if (arr[i] > arr[i + 1]) {
                    int t = arr[i];                                                         // Swapping or Bubbling Up :: arr[i] with arr[i+1] ...
                    arr[i] = arr[i + 1];
                    arr[i + 1] = t;
                    flag = 1;                                                                  // Flag will tell, current run was necessary...
                    swaps++;
                }
            }
            if (flag == 0)
                break;
        }
        System.out.print("\nINFO: Swapping Done, Total swaps :: " + swaps);
        // Counter of Swappings...
    }
}

/*             -: OUTPUT :-
====== Before Sorting ======
 30 20 10 70 60 80 50 40

INFO: Swapping Done, Total swaps :: 11


======= After Sorting ======
 10 20 30 40 50 60 70 80

======= Already Sorted ======
INFO: Swapping Done, Total swaps :: 0

*/

Q51. How to Sort an Array using Quick Sort?

It’s one of the top Core Java Interview Questions for Experienced candidates as well.
Quicksort is one of the fastest sorting algorithms that makes (n log n) comparisons in average case for sorting of an array of n elements. Quick Sort follows “Divide And Conquer” approach.
Almost all of the built-in Sorting functions provided by Programming Languages including (C++, Ruby, JavaScript, PHP etc.) internally use Quick Sort or its variant.
Here is the Complete implementation of Quick Sort:

package com.shubhamklogic.java.interview.questions;

public class QuickSortInJavaSolution {

    public static void main(String[] args) { // main() method

        int[] arr = { 30,  20,  40,  10,  80,  50,  60,  70 };                   // Unsorted Array

        System.out.print("\n===== Before Sorting =====");
        print(arr);

        Quicksort(arr, 0, arr.length - 1);                                              // Calling QuickSort()...

        System.out.print("\n===== After Sorting =====");
        print(arr);
    }
    public static void Quicksort(int[] arr, int start, int end) {    // QuickSort() body...

        if (start < end) {
            int pIndex = getPartitioningIndex(arr, start, end);     // Get the partitioning index
            Quicksort(arr, start, pIndex - 1);                                      // Sort the first half: from start to partition_index-1
            Quicksort(arr, pIndex + 1, end);                                      // Sort the other half: from partition_index+1 to end
        }
    }

    public static int getPartitioningIndex(int[] arr, int start, int end) {

        int pivot = arr[end];                                          // In the beginning, set the last element as pivot
        int pIndex = start;                                            // Set the first index as partitioning_index as it will adjust accordingly

        for (int i = start; i < end; i++) {
            if (arr[i] <= pivot)                                        // Checking if any element is lesser than the pivot
            {                                                                       // If true, swap the value at partitioning_index with that lesser_value
                int temp = arr[i];
                arr[i] = arr[pIndex];
                arr[pIndex] = temp;

                pIndex++;                                                // Increment... partitioning_index
            }
        }
        int temp = arr[end];                                     // At last - just swap partitioning_index value with pivot (or arr[end])
        arr[end] = arr[pIndex];
        arr[pIndex] = temp;
        return pIndex;                                             // Return partitionIndex...
    }
    public static void print(int[] arr) {
        for (int n: arr) {
            System.out.print(" " + n);
        }
    }
}

/*      -: OUTPUT :-
===== Before Sorting ===== 
30 20 40 10 80 50 60 70

===== After Sorting ======
10 20 30 40 50 60 70 80
*/