Calculador.java

import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.AbstractList;
import java.util.ArrayList;

//Calculador de números primos do Allan Taborda -  Autor: Allan Taborda ds Santos - Licença: GPL 3
public class Calculador{
    private PersistentListOfIntegers primos;
    private int count = 0, max;

    public Calculador(){
        primos = new PersistentListOfIntegers("NumerosPrimos.dat");
        if(primos.isEmpty()){
            max = 14;
            primos.add(2);
            primos.add(3);
            primos.add(5);
            primos.add(7);
            primos.add(11);
            primos.add(13);
            primos.add(17);
            primos.add(19);
            primos.add(23);
            primos.add(29);
            for(int n : primos) System.out.println("O numero " + n + " e primo!");
        }else{
            max = (primos.get(primos.size() - 1) - 1) / 2;
        }
        for(int n = primos.get(primos.size() - 1); n < Integer.MAX_VALUE; n = n + 2){
            if(isPrimo(n)){
                primos.add(n);
                System.out.println("O numero " + n + " e primo!");
                if(primos.size() % 100 == 0) System.out.println("Quantidade de numeros primos encontrada: " + primos.size());
                if(primos.size() == 10000000) primos.finish();
                if(++count > 9999){
                    count = 0;
                    System.out.print("Salvando...");
                    primos.save();
                    System.out.println("   OK!");
                }
            }
            max = (n - 1) / 2;
        }
    }

    public boolean isPrimo(long n){
        for(int c = 1; c < primos.size(); c++){
            long p = primos.get(c);
            if(p > max) return true;
            if(n % p == 0) return false;
        }
        throw new RuntimeException("Essa linha nunca deveria ser executada!");
    }

    public static void main(String[] nerds){
        new Calculador();
    }

    private class PersistentListOfIntegers extends AbstractList<Integer>{
        private ArrayList<Integer> ints;
        private final String nome;

        public PersistentListOfIntegers(String nome){
            this.nome = nome;
            ints = new ArrayList<Integer>(10000000);
            load();
        }

        @Override
        public Integer get(int index){
            return ints.get(index);
        }

        @Override
        public int size(){
            return ints.size();
        }

        @Override
        public boolean add(Integer n){
            return ints.add(n);
        }

        @SuppressWarnings("unchecked")
        public void load(){
            try{
                File f = new File(nome);
                if(f.isFile()){
                    ObjectInputStream ois = new ObjectInputStream(new BufferedInputStream(new FileInputStream(f), 1638400));
                    ints = (ArrayList<Integer>) ois.readObject();
                    ois.close();
                }else{
                    ints = new ArrayList<Integer>(10000000);
                }
            }catch(Exception e){
                System.out.println("ZICOU!!!");
                e.printStackTrace();
                System.exit(1);
            }
        }

        public void save(){
            try{
                ObjectOutputStream oos = new ObjectOutputStream(new BufferedOutputStream(new FileOutputStream(new File(nome)), 1638400));
                oos.writeObject(ints);
                oos.flush();
                oos.close();
            }catch(Exception e){
                System.out.println("ZICOU!!!");
                e.printStackTrace();
                System.exit(1);
            }
        }

        public void finish(){
            save();
            new File(nome).renameTo(new File("Concluido" + nome));
        }
    }
}