**In almost all interview these programming questions are asking by interviewer.**

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

```
package practice.Number;
public class PrimeNumber {
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.

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 number.

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>();
al.add(1);
al.add(2);
al.add(3);
al.add(3);
al.add(4);
al.add(5);
System.out.println(al);
Set<Integer> hs= new HashSet<Integer>(al);
System.out.println(hs);
}
}

#### 4. Check Palindrome Number.

package practice.Number;
public class PalindromeNumber {
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.

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];
}
return total;
}
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.

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]);
}
}
}
}
}

Hope this was helpful for you. If you have any questions please feel free to leave a comment. Thank you for reading.

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