Java Coding Interview Questions with Answers

Write the java code to check prime numbers.

import java.util.Scanner;

public class Prime1 {

public static void main(String[] args) {

Scanner sc=new Scanner(System.in);

System.out.print("Enter the number:");

int number = sc.nextInt();

sc.close();

boolean flag = false;

for(int i=2;i<=number/2;i++){

if(number%i==0){

flag=true;

break;

}

}

if(number<2 || flag){

System.out.println("Not Prime");

}else if(!flag){

System.out.println("Prime Number");

}

}

}

Output Screen:

Enter the number:23

Prime Number

Second Approach****************

import java.util.Scanner;

import java.lang.Math;

public class Prime2 {

public static void main(String[] args) {

Scanner sc=new Scanner(System.in);

System.out.print("Enter the number:");

int number = sc.nextInt();

sc.close();

boolean flag = false;

double sqrt = Math.sqrt(number);

if(Math.floor(sqrt)==sqrt){

flag=true;

}

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

if(number%i==0){

flag=true;

break;

}

}

if(number<2 || flag){

System.out.println("Not Prime");

}else if(!flag){

System.out.println("Prime Number");

}

}

}

Output Screen:

Enter the number:37

Prime Number

Third Approach*****************

import java.util.Scanner;

public class Prime3{

public static void main(String[] args) {

Scanner sc=new Scanner(System.in);

System.out.print("Enter the number:");

int number = sc.nextInt();

sc.close();

int i;

for(i=2;i<=number/2;i++){

if(number%i==0){

break;

}

}

if(number<2 || i< (number/2)+1){

System.out.println("Not Prime");

}else if (i== (number/2)+1){

System.out.println("Prime Number");

}

}

}

Output Screen:

Enter the number:12

Not Prime

Java Code to exchange the row into column.

public class Row_Column {

public static void main(String args[]){

int arr[][]={{1,2,3},{4,5,6},{7,8,9}};

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

for(int j=0;j<arr.length;j++){

System.out.print(arr[i][j]+" ");

}

System.out.println();

}

System.out.println("After Exchange");

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

for(int j=0;j<arr.length;j++){

System.out.print(arr[j][i]+" ");

}

System.out.println();

}

}

}

Output Screen:

1 2 3 

4 5 6 

7 8 9 

After Exchange

1 4 7 

2 5 8 

3 6 9 

Java code to sort an array.

public class Sort_Array {

public static void main(String[] args) {

int arr[]={1,34,9,14,90};

for(int i:arr)System.out.print(i+" ");

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

for(int j=i+1;j<arr.length;j++){

if(arr[j]<arr[i]){

int temp = arr[i];

arr[i]=arr[j];

arr[j]=temp;

}

}

}

System.out.println();

for(int a:arr)System.out.print(a+" ");

}

}

Output Screen:

1 34 9 14 90 

1 9 14 34 90 

Java code to print fibonacci series.

import java.util.Scanner;

public class Fibonacci {

public static void main(String[] args) {

Scanner sc=new Scanner(System.in);

System.out.print("How many number you want:");

int count=sc.nextInt();

sc.close();

int x=0,y=1,z;

System.out.print(x+", "+y);

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

z=x+y;

System.out.print(", "+z);

x=y;

y=z;

}

}

}

Output Screen:

How many number you want:10

0, 1, 1, 2, 3, 5, 8, 13, 21, 34

Java code to reverse a number.

import java.util.Scanner;

public class Reverse_Number {

public static void main(String[] args) {

Scanner sc=new Scanner(System.in);

System.out.print("Enter the number: ");

int number = sc.nextInt();

sc.close();

int reverse=0;

while(number!=0){

int remainder = number%10;

reverse = reverse*10+remainder;

number = number/10;

}

System.out.println("Reverse number is: "+reverse);

}

}

Output Screen:

Enter the number: 123456

Reverse number is: 654321

Java code to calculate factorial of number.

public class Factorial {

public static void main(String[] args) {

int number = 6;

System.out.println("Factorial of "+number+" is: "+factorial(number));

}

static int factorial(int n){

if(n==0||n==1) return 1;

else return n*factorial(n-1);

}

}

Output Screen:

Factorial of 6 is: 720