CheckCollatzMT.java

import java.math.BigInteger;
import java.util.ArrayList;
import java.util.Date;

// Collatz.check() checks the Collatz conjecture for a given
// number n.

// Now, to prove the conjecture to be correct, we would need to
// to verify it for all n.
// This is not possible to check for all n with a given computer
// but at least we can check for several values.
//
public class CheckCollatz {

    private final static BigInteger ONE = new BigInteger("1");

    // Check the conjecture for 1 <= i <= n
    public static boolean check(BigInteger n) {
        // TODO complete

        int core = Runtime.getRuntime().availableProcessors();
        BigInteger s = n.divide(new BigInteger(String.valueOf(core)));

        ArrayList<CalcCheckCollatz> threadList = new ArrayList<>();
        for (int i = 0; i < core; i++) {
            CalcCheckCollatz calcCheckCollatz = new CalcCheckCollatz(new BigInteger(String.valueOf(i)).multiply(s),
                    new BigInteger(String.valueOf(i)).multiply(s).add(s).subtract(ONE));
            calcCheckCollatz.start();
            threadList.add(calcCheckCollatz);
        }

        for (CalcCheckCollatz calcCheckCollatz : threadList) {
            try {
                calcCheckCollatz.join();
            } catch (Exception e) {
                e.printStackTrace();
            }
        }

        return true;
    }

    public static void main(String[] args) {

        if (args.length != 1) {
            System.out.println("Usage:");
            System.out.println("java CheckCollatz n");
            System.out.println("will check the Collatz conjecture for");
            System.out.println("every 1 <= i <= n");
            System.exit(1);
        }

        long start_time = new Date().getTime();
        boolean v = CheckCollatz.check(new BigInteger(args[0]));
        long end_time = new Date().getTime();
        System.out.println("Ellapsed time: " + (end_time - start_time) + "ms");

        if (v) {
            System.out.println("The conjecture seems valid up to n=" + args[0]);
        } else {
            System.out.println("The conjecture is not valid");
        }
    }
}

class CalcCheckCollatz extends Thread {
    private BigInteger lower;
    private BigInteger upper;

    CalcCheckCollatz(BigInteger lower, BigInteger upper) {
        this.lower = lower;
        this.upper = upper;
    }

    @Override
    public void run() {
        while (upper.compareTo(lower) > 0) {
            boolean result = Collatz.judgmentResult(upper);

            if (!result) {
                return;
            }
            upper = upper.subtract(BigInteger.ONE);
        }
    }
}

ThreadSample.java

public class ThreadSample {

    public static void main(String[] args) {

        int core = Runtime.getRuntime().availableProcessors();

        int n = core * 10;

        int s = n / core;

        System.out.println(core);
        System.out.println(n);
        System.out.println(s);

        for (int i = 0; i < core; i++) {
            new CalcCollatz(i * s, i * s + s - 1).start();
        }
    }
}

class CalcCollatz extends Thread {
    private int lower;
    private int uppper;

    CalcCollatz(int lower, int upper) {
        this.lower = lower;
        this.uppper = upper;
    }

    @Override
    public void run() {
        System.out.println("lower = " + lower + " upper = " + uppper);
    }
}