Please help my.Insorrect result.

[ladislav]

Please help my.My program is running but print in
"System.out.println(firstprime.findPrime ());" isn't
correct.It prin except string primenumbers some other
number for example 16 or 64(it isn't primenumbers).
I thynk that problem is in method "testIsPrime"
but I cannot find it.


/**
*PrimeNumber.java
*
*
*
* To change this template, choose Tools | Template Manager
* and open the template in the editor.
*/
//package TestPrime;
/**
*
* @author lm
*/
public class PrimeNumber{

private int numberOf = 1;
private int numberTo = 100;

public PrimeNumber() {
}

public void setOf(int number) {
numberOf = number;
}

public void setTo(int number) {
numberTo = number;
}

private boolean testIsPrime(int testprime) {
boolean prime = true;
for(int k = 3; k < testprime; k++) {//changed here
if (prime){
for(int j=2;j<=Math.sqrt(testprime);j++) {
if(testprime%k==0){
prime=false;
break;
}
}
}
}
return prime;
}

public String isPrime(int testprime) {
if ( testIsPrime(testprime)) {
return testprime+" is prime";
}else{
return testprime+" isn't prime";
}
}

public String findPrime(){
String s = "";
for(int j=numberOf;j<= numberTo;j++) {
if ( testIsPrime(j)) {
s = s + j+"is primenumber\n";
}
}
return s;

}

public static void main(String[] args) {

PrimeNumber firstprime = new PrimeNumber();

firstprime.numberOf = 10;
firstprime.numberTo = 40;
System.out.println(firstprime.findPrime ());
System.out.println(firstprime.isPrime(4272));
System.out.println(firstprime.isPrime(3517));
}
}

[r035198x]

Check again. When I run the program below it prints all the primes form 11 to 37 correctly

 
 
/**
*PrimeNumber.java
*
*
*
* To change this template, choose Tools | Template Manager
* and open the template in the editor.
*/
//package TestPrime;
/**
*
* @author lm
*/
public class PrimeNumber2{
 
private int numberOf = 1;
private int numberTo = 100; 
 
 
 
public void setOf(int number) {
numberOf = number;
}
 
public void setTo(int number) {
numberTo = number;
}
 
private boolean testIsPrime(int testprime) {
boolean prime = true;
for(int k = 3; k < testprime; k++) {//changed here
if (prime){
for(int j=2;j<=Math.sqrt(testprime);j++) {
if(testprime%k==0){
prime=false;
break;
}
}
}
}
return prime;
}
 
public String isPrime(int testprime) {
if ( testIsPrime(testprime)) {
return testprime+" is prime";
}else{
return testprime+" isn't prime";
}
}
 
public String findPrime(){
String s = "";
for(int j=numberOf;j<= numberTo;j++) {
if ( testIsPrime(j)) {
s = s + j+"is primenumber\n";
}
}
return s;
 
}
 
public static void main(String[] args) {
 
PrimeNumber2 firstprime = new PrimeNumber2();
 
firstprime.numberOf = 10;
firstprime.numberTo = 40;
System.out.println(firstprime.findPrime ());
System.out.println(firstprime.isPrime(4272));
System.out.println(firstprime.isPrime(3517));
}
}
 
 
 

[ladislav]

Thant you I try it

[r035198x]

Thant you I try it

Is it working?

[Ganon11]

private boolean testIsPrime(int testprime) {
    boolean prime = true;
    for(int k = 3; k < testprime; k++) {//changed here
        if (prime) {
            for(int j = 2; j <= Math.sqrt(testprime); j++) {
                if (testprime % k== 0) {
                    prime=false;
                    break;
                }
            }
        }
    }
    return prime;
}

In your second if statement, shouldn't you be modding testprime by j, not k? i.e.

private boolean testIsPrime(int testprime) {
    boolean prime = true;
    for(int k = 3; k < testprime; k++) {//changed here
        if (prime) {
            for(int j = 2; j <= Math.sqrt(testprime); j++) {
                if (testprime % j == 0) {
                    prime=false;
                    break;
                }
            }
        }
    }
    return prime;
}