# Common Java interviewing questions

In this article, we are going to discuss the top 10 very important programming interviewing questions which are almost all interviews are asking by the interviewer.

#### 1. Check Number is Prime number or not.

These are very important interviewing questions that are asking at both fresher level and experience level.

``````package practice.Number;

public static void main(String Ars[]) {
int i, m = 0, flag = 0;
int n = 5;
m = n / 2;
if (n == 0 || n == 1) {
System.out.println(n + " " + "Not prime number");
} else {
for (i = 2; i <= m; i++) {
if (n % i == 0) {
System.out.println(n + " " + "Not prime number");
flag = 1;
break;
}
}
if (flag == 0) {
System.out.println(n + " " + "is prime number");
}
}
}
}
``````

#### 2. Reverse number in java.

This is programming question is a very common question for every interview,  using this equation interviewer is checking your logical concept.

Step 1:- First we need to check number is greater than 0 or not in the while loop.

Step 2:- If the number is greater than 0 then we need to find a mode of that number.

Step 3:- Then we need to divide the number by 10.

Step 4:- After that, we need to store that number(r) in a global variable and we need to multiple r to 10 and add that mode of number, this process we need to do until the number will become zero.

``````package practice.Number;

public class ReverceNumber {

public static void main(String[] args) {
int n = 123;
int r = 0;
while (n > 0) {
int m = n % 10;
n = n / 10;
r = r * 10 + m;
}
System.out.println("Reverce number of number is " + r);
}
}``````

#### 3. Remove Duplicates numbers.

If we want to remove a duplicate number without any other operation than, we need to simply set that list of numbers into a set, so the set will internally useing the sorting technique.

``````package practice.Number;

import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

public class RemovedDuplicates {

public static void main(String[] args) {
List<Integer> al= new ArrayList<Integer>();
System.out.println(al);
Set<Integer> hs= new HashSet<Integer>(al);
System.out.println(hs);
}
}
``````

#### 4. Check Palindrome Number.

Find palindrome number is the same as finding reverse numbers, which I already explain in the reverse programming question.

``````package practice.Number;

public static void main(String Arg[]) {
int n = 121;
int temp = n;
int sum = 0;
while (n > 0) {
int m = n % 10;
n = n / 10;
sum = (sum * 10 )+ m;
}
if (sum == temp) {
System.out.println(sum + " number is palindrome");
} else {
System.out.println(sum + " number is not palindrome");
}
}
}``````

#### 5. Missing Number from Array.

This programming question asking for checking your array concept. They are checking how we think to solve this type of question.

``````package practice.Number;

public class MissingNumber {
static int getMissingNumber(int num[], int n) {
int i, total;
total = (n + 1) * (n + 2) / 2;
for (i = 0; i < n; i++) {
total -= num[i];
}

}

public static void main(String[] args) {
int num[] = {1, 2, 3, 4, 5, 6, 8, 9 };
int miss = getMissingNumber(num, num.length);
System.out.println(miss);

}

}``````

#### 6.Fibonacci Series.

Fibonacci series without Recursion.

``````package practice.Number;

public class FibonacciSeries {
public static void main(String Arg[]) {
int n=10, n1=0, n2=1,n3;
System.out.print(n1+" "+n2);
for(int i=2;i<n;i++) {
n3=n1+n2;
System.out.print(" "+ n3);
n1=n2;
n2=n3;
}
}
}``````

Fibonacci series with Recursion.

``````package practice.Number;

public class FibonacciSeriesRecursion {
static int i, n1=0,n2=1,n3;
static void printFibonaicc(int n) {
if(n>0) {
n3= n1+n2;
n1=n2;
n2=n3;
System.out.print(" "+n3);
printFibonaicc(n-1);
}
}
public static void main(String Ags[] ) {
int n=10;
System.out.print(n1+" "+n2);
printFibonaicc(n-2);
}
}
``````

#### 7. Check Armstrong Number.

Finding Armstrong’s number is the same as the reverse number concept but at the last we need to multiple mode three times when we are adding.

``````package practice.Number;

public class Armstrongnumber {

public static void main(String[] args) {
int n = 153;
int s = 0, temp = 153;
while (n > 0) {
int m = n % 10;
n = n / 10;
s = s + (m * m * m);
}
if (temp == s) {
System.out.println("Number is Armstrong");
} else {
System.out.println("Number is not Armstrong");
}
}
}``````

#### 8. Factorial Number.

``````package practice.Number;

public class Factorial {

public static void main(String[] args) {
int n=5;
int f = 1;
while(n>0) {
f=(f*n);
n--;
}
System.out.println("Factorial of n : "+f);
}
}``````

#### 9. Square Root of Number.

``````package practice.Number;

public class SquareRoot {

public static void main(String[] args) {
Double num = 4.0;
int n = 4;
System.out.println("SquareRoot of number is : " + Math.sqrt(num));
System.out.println("SquareRoot of number is : " + Math.pow(num, 2));
System.out.println("SquareRoot of number is : " + Math.pow(num, 3));

for (int i = 1; i <= n; i++) {
int reminder = n % i;
if (reminder == 0 && (n / i) == i) {//if reminder is 0 and number divided by i is same i than number is square root
System.out.println("The Square root of " + n + " is = " + i);
}
}
}
}``````

#### 10. Print duplicate element.

``````package practice.Number;

public class DuplicateElement {
public static void main(String Arg[]) {
int nums[] = { 1, 2, 3, 4, 5, 5, 6, 7 };
int l = nums.length;
for (int i = 0; i < l; i++) {
for (int j = i + 1; j < l; j++) {
if (nums[i] == nums[j]) {
System.out.println(nums[i]);
}
}
}
}
}``````

Read more topics related to java