JavaClasses/src/main/java/mattrixwv/SieveOfEratosthenesBig.java

//JavaClasses/src/main/java/mattrixwv/SieveOfEratosthenesBig.java
//Matthew Ellison
// Created: 06-30-21
//Modified: 06-30-21
//This class uses to Sieve of Eratosthenes to generate an infinite number of primes
/*
Copyright (C) 2021  Matthew Ellison

	This program is free software: you can redistribute it and/or modify
	it under the terms of the GNU Lesser General Public License as published by
	the Free Software Foundation, either version 3 of the License, or
	(at your option) any later version.

	This program is distributed in the hope that it will be useful,
	but WITHOUT ANY WARRANTY; without even the implied warranty of
	MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
	GNU Lesser General Public License for more details.

	You should have received a copy of the GNU Lesser General Public License
	along with this program.  If not, see <https://www.gnu.org/licenses/>.
*/
package mattrixwv;


import java.math.BigInteger;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;


public class SieveOfEratosthenesBig implements Iterator<BigInteger>{
	BigInteger possiblePrime;
	private Map<BigInteger, ArrayList<BigInteger>> dict;

	public SieveOfEratosthenesBig(){
		dict = new HashMap<BigInteger, ArrayList<BigInteger>>();
		possiblePrime = BigInteger.TWO;
	}
	@Override
	public boolean hasNext(){
		return true;
	}
	@Override
	public BigInteger next(){
		BigInteger prime;
		if(possiblePrime.compareTo(BigInteger.TWO) > 0){
			//Loop until you find a prime number
			for(;dict.containsKey(possiblePrime);possiblePrime = possiblePrime.add(BigInteger.TWO)){
				//Create the next entry for all entries in the map
				for(BigInteger num : dict.get(possiblePrime)){
					BigInteger loc = possiblePrime.add(num).add(num);
					if(!dict.containsKey(loc)){
						ArrayList<BigInteger> tempArray = new ArrayList<BigInteger>(Arrays.asList(num));
						dict.put(loc, tempArray);
					}
					else{
						dict.get(loc).add(num);
					}
				}
				//Delete the current entry
				dict.remove(possiblePrime);
			}
			//Save that the number is a prime
			prime = possiblePrime;
			BigInteger loc = prime.multiply(BigInteger.valueOf(3));
			if(!dict.containsKey(loc)){
				ArrayList<BigInteger> tempArray = new ArrayList<BigInteger>(Arrays.asList(prime));
				dict.put(loc, tempArray);
			}
			else{
				dict.get(loc).add(prime);
			}
			//Move on to the next possible prime
			possiblePrime = possiblePrime.add(BigInteger.TWO);
		}
		else{
			//Return 2 and move to 3
			prime = possiblePrime;
			possiblePrime = possiblePrime.add(BigInteger.ONE);
		}
		return prime;
	}
}