This question already has answers here:
Java: Error: variable might not have been initialized
(2 answers)
Closed 4 years ago.
I don't know what is wrong with this code and why it is giving the error:
Variable isPrime might not have been initialized
This is the complete code:
import java.util.Scanner;
public class PrimeNumberTest {
//Program to test for prime numbers
public static void main(String[] args) {
Scanner prime = new Scanner(System.in);
int number;
boolean isPrime;
System.out.print("Please enter number: ");
number = prime.nextInt();
if (number < 2)
isPrime = false;
else{
for (int i = 2; i < number / 2; i++)
if (number % i == 0){
isPrime = false;
break;
}
}
if (isPrime)
System.out.println("Your number is a prime number");
else
System.out.println("Your number is not a prime number");
}
}
boolean isPrime = false;
Just initialize isPrime boolean.
Related
This question already has answers here:
How to determine if a number is prime
(7 answers)
Closed 6 months ago.
write a program in java using object oriented principle to check whether a number is prime or not. If it is prime then print 1 if it is false then 0 if the given value is less then or equal to 1 then print -1. Take the values from the user?
when i give single digit values it works but when i give 2 digits value it doesn't work
import java.util.Scanner;
class Prime1 {
int n;
Prime1 (int n)
{
this.n=n;
}
boolean isPrime()
{
if(n==2)
{
System.out.println("1");
return true;
}
else if (n%2==0)
{
System.out.println("0");
return false;
}
for (int i = 3;i<=Math.sqrt(n);i+=2)
{
if(n%i==0)
System.out.println("0");
return false;
}
System.out.println("1");
return true;
}
}
class CheckPrime
{
public static void main(String[] args)
{
System.out.print("Enter a number you want to check :: ");
Scanner scan = new Scanner(System.in);
int num1 = scan.nextInt();
scan.close();
Prime1 obj = new Prime1(num1);
if(num1<=1)
{
System.out.print("-1");
}
else
{
obj.isPrime();
}
}
}
change the for loop to
for (int i = 3;i<=Math.sqrt(n);i+=2)
{
if(n%i==0)
{
System.out.println("0");
return false;
}
}
You forgot to put curly bracket after if which results in for loop running only once!
public class PrimeNumbers {
public static void main(String[] args) {
int num = 6;
boolean isPrime = true;
for (int i = 2; i <= num - i; i++) {
if (num % i == 0) {
isPrime = false;
break;
}
}
int nextPrime = num++;
{
while (isPrime = false) {
}
if (isPrime)
System.out.println("Is a prime number");
else
System.out.println("Is not a prime number" + "the next prime number is" + nextPrime(num));
}
}
}
I have tried to code in Java in order to find the next prime number while the previously returned is false, but I am really confused about how to proceed with "while" code. This is what I have tried until now:
You can create two functions: one (say, isPrime) to check if the number is prime or not and the second (say, nextPrime) to find the next prime. The logic in the second function will be quite straight forward: keep incrementing the number by 1 until isPrime returns true.
Note that you need to check only up to the square root of the number in order to determine if it is prime. Check https://en.wikipedia.org/wiki/Primality_test to learn more about it.
Demo:
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner scanner = new Scanner(System.in);
System.out.print("Enter an integer: ");
int n = scanner.nextInt();
if (isPrime(n)) {
System.out.println("It is a prime number");
} else {
System.out.println("It is not a prime number. The next prime number is " + nextPrime(n));
}
}
static boolean isPrime(int n) {
if (n == 1 || n == 0) {
return false;
}
for (int i = 2; i <= Math.sqrt(n); i++) {
if (n % i == 0) {
return false;
}
}
return true;
}
static int nextPrime(int n) {
while (!isPrime(n)) {
n++;
}
return n;
}
}
A sample run:
Enter an integer: 10
It is not a prime number. The next prime number is 11
Another sample run:
Enter an integer: 11
It is a prime nmber
How about this snippet?
public static void main(String[] args) {
int number= 14; // will print the second SOUT statement with 17
if (isPrime(number)) {
System.out.println(number+ " is a prime number");
} else {
System.out.println(number+ " is not a prime number, " +
"the next prime number is " + nextPrime(number));
}
}
/**
* Check if the number is a prime number
* For 0 or 1 you can return false, for the rest if is divisible by each number
* You might want to throw an exception for the negative input
*/
static boolean isPrime(int number) {
if (number==0 || number==1) {
return false;
}
for (int i=2; i<=number/2; i++) {
if (number%i==0) {
return false;
}
}
return true;
}
/**
* Iterate the number by one until you find a prime number using the while cycle
*/
static int nextPrime(int number) {
int prime;
while (true) {
boolean isPrime = isPrime(++number);
if (isPrime) {
prime = number;
break;
}
}
return prime;
}
In order to find a prime number, you basically need a nested loop. So I'd recomend having your for loop INSIDE the while loop. OR you can have a do-while loop on the outside that keeps looping until you found a prime number.
Your code should look like this:
public class PrimeNumbers {
public static boolean check_prime(int num){
for (int i = 2; i <= num-i ; i++) {
if (num % i == 0) {
return false;
}
}
return true;
}
public static void main(String[] args){
int num = 6;
boolean isPrime= true;
if(!check_prime(6)){
int nextPrime = num;
do{
nextPrime++;
if (check_prime(nextPrime)) {
isPrime = true;
break;
}else{
isPrime = false;
}
}while(!isPrime);
}
if (isPrime)
System.out.println("Is a prime number");
else
System.out.println("Is not a prime number" +"the next prime number is" + nextPrime);
}}}
Closed. This question is not reproducible or was caused by typos. It is not currently accepting answers.
This question was caused by a typo or a problem that can no longer be reproduced. While similar questions may be on-topic here, this one was resolved in a way less likely to help future readers.
Closed 6 years ago.
Improve this question
Below is the code for a java programming class I am writing. I cannot figure out why it always prints it is a prime number (true) reguardless of the int I input. Thank you in advance. Jared
import java.util.*;
public class PrimeNumbersExample
{
public static void main(String[] args)
{
int myInt = 0;
Scanner kb = new Scanner(System.in);
System.out.println("Please enter a number: ");
myInt = kb.nextInt();
boolean isPrime = true;
{
for (int i = 2; i < myInt; i++) // exclude 1 and the variable num from the diviso
if (myInt % i == 0)
isPrime = false;
}
if (isPrime=true)
System.out.println("It is a Prime number.");
else if (isPrime=false)
System.out.println("the number is NOT PRIME");
}
}
You are not doing the comparison correctly. You just have to say if(isPrime) instead of if(isPrime=true) because isPrime is already a boolean.
System.out.println(isPrime ? "Prime" : "Non-Prime");
Even if you want to do a comparison you should be using == instead of just =.
if (isPrime == true) {
System.out.println("It is a Prime number.");
} else {
System.out.println("the number is NOT PRIME");
}
Additionally, you can use a break statement inside your if to make it stop once the number is identified as Non-Prime.
for (int i = 2; i < myInt; i++) {
if (myInt % i == 0) {
isPrime = false;
break;
}
}
Here is the corrected code snippet:
public static void main(String[] args)
{
int myInt = 0;
Scanner kb = new Scanner(System.in);
System.out.println("Please enter a number: ");
myInt = kb.nextInt();
boolean isPrime = true;
for (int i = 2; i < myInt; i++) { // exclude 1 and the variable num from the diviso
if (myInt % i == 0) {
isPrime = false;
break;
}
}
System.out.println(isPrime ? "Prime" : "Non-Prime");
}
In the line, if (isPrime=true) what you are going to do is to check whether the isPrime is true, but what the exactly happening is it assign the value true to isPrime and evaluate to true inside the if condition. So what you exactly should do is if (isPrime==true). The corrected code is as follows,
import java.util.*;
public class PrimeNumbersExample
{
public static void main(String[] args)
{
int myInt = 0;
Scanner kb = new Scanner(System.in);
System.out.println("Please enter a number: ");
myInt = kb.nextInt();
boolean isPrime = true;
{
for (int i = 2; i < myInt; i++) // exclude 1 and the variable num from the diviso
if (myInt % i == 0)
isPrime = false;
}
if (isPrime==true)
System.out.println("It is a Prime number.");
else if (isPrime==false)
System.out.println("the number is NOT PRIME");
}
}
*Note - also you can directly use isPrime variable inside the if condition since it is Boolean
The statement if (isPrime=true) is actually just assigning the value true to the isPrime variable which will always return true. That's why the first condition is always executed
You can just simply do it like this :
if (isPrime) {
System.out.println("It is a Prime number.");
} else {
System.out.println("the number is NOT PRIME");
}
Also, always put braces for readability
Try this one.
public class MyPrimeNumCheck {
public boolean isPrimeNumber(int number){
for(int i=2; i<=number/2; i++){
if(number % i == 0){
return false;
}
}
return true;
}
public static void main(String a[]){
MyPrimeNumCheck mpc = new MyPrimeNumCheck();
System.out.println("Is 17 prime number? "+mpc.isPrimeNumber(17));
System.out.println("Is 19 prime number? "+mpc.isPrimeNumber(19));
System.out.println("Is 15 prime number? "+mpc.isPrimeNumber(15));
}
}
This question already has answers here:
How do I generate random integers within a specific range in Java?
(72 answers)
Closed 7 years ago.
here is the whole code how do I in this create random number so that numberneedingtobeguessed is generated randomly.
public class Guessing {
public static void main(String[] args) {
// TODO Auto-generated method stub
#SuppressWarnings("resource")
Scanner input = new Scanner(System.in);
int number;
int numberneedingtobeguessed = 26;
int done = 1;
System.out.println("I am thinking of a number in between 1 and 50 what is it?");
while (done < 2) {
number = input.nextInt();
if (number < numberneedingtobeguessed) {
System.out.println("Too low");
}
else if (number > numberneedingtobeguessed) {
System.out.println("Too high");
}
else if (number == numberneedingtobeguessed) {
System.out.println("You guessed correctly");
done = done + 1;
}
}
}
}
import java.util.Random;
.........
Random ran = new Random();
int r = ran.nextInt(50) + 1;
This will generate a random number between 0 ... 49 and then add 1 at the end.
This question already has answers here:
Java Display the Prime Factorization of a number
(7 answers)
Closed 9 years ago.
I need this to output factors as prime numbers only.
public static void main(String[] args) {
Scanner keyboard = new Scanner(System.in);
System.out.println("Enter a number:");
int theNum = keyboard.nextInt();
int i;
System.out.println("\nThe prime factors of " + theNum + " are:");
for(i=1; i <= theNum/2; i++)
if(theNum % i == 0)
{
System.out.print(i + " ");
}
}
}
You basically just need to check for prime numbers
Some prime-number check function I copied from here:
boolean isPrime(int n) {
//check if n is a multiple of 2
if (n%2==0) return false;
//if not, then just check the odds
for(int i=3;i*i<=n;i+=2) {
if(n%i==0)
return false;
}
return true;
}
Then just add the isPrime(i) check:
public static void main(String[] args) {
Scanner keyboard = new Scanner(System.in);
System.out.println("Enter a number:");
int theNum = keyboard.nextInt();
System.out.println("\nThe prime factors of " + theNum + " are:");
for(int i = 1; i <= theNum / 2; i++)
if (theNum % i == 0 && isPrime(i))
System.out.print(i + " ");
}
Test.