How it improve

[ladislav]

I made this program test prime.
I want it improve I have idea but I don’t now how it insert in into program.
Howe somebody else idea?


My idea: if(prime[i]==true)
i*i==false;
Thank for your help


public class testPrime{
public static void main(String[] args) {

int limit = 1000;
int i,j;
boolean []prime=new boolean[limit+1];

for( i=1;i<=limit;i+ +){
prime[i]=true;

if(i%2==0)
prime[i]=false;

if((i%3==0)||(i %5==0))
prime[i]=false;

prime[1]=true;
prime[2]=true;
prime[3]=true;
prime[5]=true;

if(prime[i]==false)
continue;

for( j=2;j<i;j++){

if(i%j==0)
prime[i]=false;

}
if(prime[i]==true)
System.out.prin tln(i+" is_prime**");
else
System.out.prin tln(i+" no_prime");
}
}
}

[r035198x]

I made this program test prime.
I want it improve I have idea but I don’t now how it insert in into program.
Howe somebody else idea?


My idea: if(prime[i]==true)
i*i==false;
Thank for your help


public class testPrime{
public static void main(String[] args) {

int limit = 1000;
int i,j;
boolean []prime=new boolean[limit+1];

for( i=1;i<=limit;i+ +){
prime[i]=true;

if(i%2==0)
prime[i]=false;

if((i%3==0)||(i %5==0))
prime[i]=false;

prime[1]=true;
prime[2]=true;
prime[3]=true;
prime[5]=true;

if(prime[i]==false)
continue;

for( j=2;j<i;j++){

if(i%j==0)
prime[i]=false;

}
if(prime[i]==true)
System.out.prin tln(i+" is_prime**");
else
System.out.prin tln(i+" no_prime");
}
}
}

Now hold it right there.

From here,

 
Now hold it right there. 
public class testPrime{
public static void main(String[] args) {
int limit = 1000;
int i,j;
boolean []prime = new boolean[limit+1];
for( i=2;i<=limit;i++){
prime[i]=true;
 
 
for( j=2;j<i;j++){
if(i%j == 0)
prime[i]=false;
}
if(prime[i]==true)
System.out.println(i+" is_prime**");
else
System.out.println(i+" no_prime");
}
}
}

Go to

http://www.troubleshooters.com/codecorn/primenumbers/primenumbers.htm

and
http://www.freevbcode.com/ShowCode.asp?ID=1059

Hope you can follow the algorithms here because they were not written in java.

[ladislav]

I want only discart multiple of prime numbers before second loop = i*i
I don't know how to do it in array.

[maverick19]

try to use this
this gives the whole list of prime nos till the limil value

public static void main(String[] args) {
		int length=1000;
		boolean []prime=new boolean[length+1];
		prime[0]=prime[1]=prime[2]=true;
	for(int j=3;j<=length;j++)
	{
		prime[j]=true;
		for(int k=2;k<j;k++)
		{
			if(j%k==0)
			{
				prime[j]=false;
				break;
			}
		}
		
	}
	for(int i=0;i<length;i++)
	{
		System.out.println(i+"   "+prime[i]);
	}

[ladislav]

Thank for your help.