Java - Iteration and Arrays

"while" loops to check a number is prime or not.

public static boolean isPrime (int n) {

  int divisor =2;

  while (divisor < n) {

    if (n%divisor == 0) {

      return false;

    }

  return true;

}

"for" loops

for (initialize; test; next) {

  statement;

}

  Equivalent to: 

initialize;

while (test) {

  statement;

}

next;

ARRAYS

initialize a list of charactors:

char[] c = new char[4]; // reference to array of charactors of any length

For strings c.length() is a method

For characters c.length is a field.

Print the primes from 1 to n using Sieve of Eratosthenes:

public static void printPrimes(int n) {

boolean[] prime = new boolean[n+1];

        int i;

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

prime[i]=true;

}

for(int divisor=2; divisor*divisor<=n; divisor++){

if(prime[divisor]){

for(i=2*divisor; i<=n; i=i+divisor){

prime[i]=false;

}

}

}

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

if(prime[i]){

System.out.print(" "+i);

}

}

}

}