Threads

import java.io.PrintStream;
import java.util.Scanner;

public class Programa {

    public static void main(String[] args) {
        try {
            Programa programa = new Programa();
            programa.executar();
        } catch (Throwable t) {
            t.printStackTrace();
        }
    }

    private final Scanner entrada = new Scanner(System.in);

    private final PrintStream saida = System.out;

    public void executar() throws Exception {
        saida.print("Quantidade de termos:  ");
        int qtdTermos = Integer.parseInt(entrada.nextLine());

        saida.print("Quantidade de threads: ");
        int qtdThreads = Integer.parseInt(entrada.nextLine());

        // criar as threads
        Thread[] threads = criarThreads(qtdThreads, qtdTermos);

        // disparar as threads
        for (Thread thread : threads) {
            thread.start();
        }

        // esperar que as threads terminem
        for (Thread thread : threads) {
            thread.join();
        }
    }

    private Thread[] criarThreads(int qtdThreads, int qtdTermos) {
        int termosPorThread = qtdTermos / qtdThreads;
        Thread[] threads = new Thread[qtdThreads];
        int numero = 1;
        for (int thread = 0; thread < qtdThreads; thread++) {
            int[] termos = new int[termosPorThread];
            for (int i = 0; i < termosPorThread; i++) {
                termos[i] = numero;
                numero++;
            }
            threads[thread] = new Thread(() -> somarTermos(termos), "Thread " + thread);
        }
        return threads;
    }

    private void somarTermos(int[] termos) {
        StringBuilder texto = new StringBuilder();
        int soma = 0;
        for (int termo : termos) {
            if (texto.length() > 0) {
                texto.append(" + ");
            }
            texto.append(termo);
            soma += termo;
            Thread.yield();
        }
        texto.append(" = ").append(soma);
        saida.println(Thread.currentThread().getName() + ": " + texto);
    }
}