Java Thread How to - Execute Callable tasks

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Question

We would like to know how to execute Callable tasks.

Answer

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
//from w  ww  . j  av  a 2s  . c  o  m
public class Main {
  public static void main(String[] args) throws InterruptedException {
    ExecutorService executor = Executors.newFixedThreadPool(Runtime
        .getRuntime().availableProcessors() + 1);
    List<Particle> allTheParticles = new ArrayList<>();
    for (int i = 0; i < 20; i++) {
      allTheParticles.add(new Particle(i, allTheParticles));
    }
    while (true) {
      executor.invokeAll(allTheParticles);
      executor.invokeAll(allTheParticles);
    }
  }
}
class Particle implements Callable<Void> {
  int id;
  int calculatedForce;
  State particleState = State.Update;
  List<Particle> allTheParticles;

  public Particle(int id, List<Particle> allTheParticles) {
    this.id = id;
    this.allTheParticles = allTheParticles;
  }

  private void calculateNetForce() {
    System.out.println("calculation in " + id);
    String someIntenseOperation = "";
    for (int i = 0; i < 10000; i++) {
      someIntenseOperation += allTheParticles.size();
    }
    System.out.println("someIntenseOperation:"+someIntenseOperation);
    calculatedForce = 0;
    particleState = State.Calculate;
  }
  private void updatePosition() {
    System.out.println("updating position of " + id);
    particleState = State.Update;
  }

  @Override
  public Void call() throws Exception {
    switch (particleState) {
    case Calculate:
      updatePosition();
      break;
    case Update:
      calculateNetForce();
      break;
    }
    return null;
  }
}
enum State {
  Update, Calculate
}

The code above generates the following result.

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