Target - find all primeNumbers and create array with it What was done - created method primeReturner - return true if number prime -
private static boolean primeReturner (int i){
for (int j=2;j<i; j++){
if (i%j==0)
return false;
}
return true;
}
created method for creating numbers with prime numbers
private static void simpleArray() {
int []a = new int [100];
a[0]=1;
a[1]=2;
for (int i=2; i<a.length; i++){
if (primeReturner(i)==true){
a[i]=i;
i++;
}
}
}
Problem - i get some errors during creating array - some of item from array 0 and some its ok... and some times it return errors...
Questing - what wrong with my method simpleArray?
A little bit modify code - now it recognize all prime numbers and create array with it, but after adding 100th item in to array i get errors
code
private static void simpleArray() {
int []a = new int [100];
a[0]=1;
a[1]=2;
int count=2;
while (count<100)
for (int i=3; ; ++i){
if (primeReturner(i)==true){
a[count]=i;
count++;
}
}
for (int j=0; j<a.length; j++){
System.out.print(" " + a[j]);
}
}
private static boolean primeReturner (int i){
for (int j=2;j<i; j++){
if (i%j==0)
return false;
}
return true;
}
and main function public class Exercise_1 { private static int select;
public static void main (String[]args) throws IOException{
System.out.println("Menu:");
....
System.out.println("Array with simple numbers - enter 7");
select = getNumber ();
switch (select){
.....
case 7:{
simpleArray();
}
}
}
As result all array with prime number succsesfull created but during printing this array i get java.lang.ArrayIndexOutOfBoundsException errors ...
How to resolve this error?
You do i++
in your if(primeReturner(i)) == true)
block. This is in addition to the for
loop i++
. You'll most likely get an ArrayIndexOutOfBoundsException
because your i
index will reach a value greater than 100, which is your array max size. Remove that i++
in the if
block.
The error is caused by the fact that you use the same variable to index in your array (ie. the index of the n-th prime), and the value of the prime. So the array constructed in simpleArray
will have a zero value if the index is non-prime or the value i
if it is prime. You need a second index if you want a fully packed array:
private static void simpleArray() {
int []a = new int [100];
a[0] = 2; // by definition 1 is not prime
int i = 1;
int possible_prime = 3;
while (i < a.length) {
if (primeReturner(possible_prime)) {
a[i++]=possible_prime;
}
possible_prime++;
}
}
For discussion of the primality of one, see Wikipedia .
for (int i=2; i<a.length; i++){
if (primeReturner(i)==true){
a[i]=i;
i++;
}
}
This is where the problem lies... remove i++ from the code
so here:
for (int i=2; i<a.length; i++){
if (primeReturner(i)==true){
a[i]=i;
}
}
Find error - need to stop loop with i by adding limit So, final code is
private static void simpleArray() {
int []a = new int [100];
a[0]=1;
a[1]=2;
int count=2;
while (count<100){
for (int i=3;**i<524** ; ++i){
if (primeReturner(i)==true){
a[count]=i;
count++;
}
}
}
for (count=0; count<a.length; count++){
System.out.print(" " + a[count]);
}
}
Think 'i<524' not the best variant, later will try to find somthing better =) thanks to all.
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