code: package io.ray.docdemo;
  
  import com.google.common.collect.ImmutableList;
  import io.ray.api.ActorHandle;
  import io.ray.api.ObjectRef;
  import io.ray.api.Ray;
  import io.ray.api.WaitResult;
  import io.ray.api.function.RayFunc0;
  import io.ray.api.function.RayFunc1;
  import java.util.ArrayList;
  import java.util.List;
  import java.util.concurrent.TimeUnit;
  import org.testng.Assert;
  
  /**
   * This class contains demo code of the Ray core walkthrough doc
   * (https://docs.ray.io/en/master/walkthrough.html).
   *
   * <p>Please keep them in sync.
   */
  public class WalkthroughDemo {
  
    public static class MyRayApp {
  
      // A regular Java static method.
      public static int myFunction() {
        return 1;
      }
  
      public static int slowFunction() throws InterruptedException {
        TimeUnit.SECONDS.sleep(10);
        return 1;
      }
  
      public static int functionWithAnArgument(int value) {
        return value + 1;
      }
  
      public static int overloadFunction() {
        return 1;
      }
  
      public static int overloadFunction(int x) {
        return x;
      }
    }
  
    public static void demoTasks() {
      // Invoke the above method as a Ray remote function.
      // This will immediately return an object ref (a future) and then create
      // a task that will be executed on a worker process.
      ObjectRef<Integer> res = Ray.task(MyRayApp::myFunction).remote();
  
      // The result can be retrieved with ``ObjectRef::get``.
      Assert.assertTrue(res.get() == 1);
  
      // Invocations of Ray remote functions happen in parallel.
      // All computation is performed in the background, driven by Ray's internal event loop.
      for (int i = 0; i < 4; i++) {
        // This doesn't block.
        Ray.task(MyRayApp::slowFunction).remote();
      }
  
      // Invoke overloaded functions.
      Assert.assertEquals(
          (int) Ray.task((RayFunc0<Integer>) MyRayApp::overloadFunction).remote().get(), 1);
      Assert.assertEquals(
          (int) Ray.task((RayFunc1<Integer, Integer>) MyRayApp::overloadFunction, 2).remote().get(),
          2);
  
      ObjectRef<Integer> objRef1 = Ray.task(MyRayApp::myFunction).remote();
      Assert.assertTrue(objRef1.get() == 1);
  
      // You can pass an `ObjectRef` as an argument to another Ray remote function.
      ObjectRef<Integer> objRef2 = Ray.task(MyRayApp::functionWithAnArgument, objRef1).remote();
      Assert.assertTrue(objRef2.get() == 2);
  
      // Specify required resources.
      Ray.task(MyRayApp::myFunction).setResource("CPU", 2.0).setResource("GPU", 4.0).remote();
  
      // Ray aslo supports fractional and custom resources.
      Ray.task(MyRayApp::myFunction).setResource("GPU", 0.5).setResource("Custom", 1.0).remote();
    }
  
    public static void demoObjects() {
      // Put an object in Ray's object store.
      int y = 1;
      ObjectRef<Integer> objectRef = Ray.put(y);
      // Get the value of one object ref.
      Assert.assertTrue(objectRef.get() == 1);
  
      // Get the values of multiple object refs in parallel.
      List<ObjectRef<Integer>> objectRefs = new ArrayList<>();
      for (int i = 0; i < 3; i++) {
        objectRefs.add(Ray.put(i));
      }
      List<Integer> results = Ray.get(objectRefs);
      Assert.assertEquals(results, ImmutableList.of(0, 1, 2));
  
      WaitResult<Integer> waitResult = Ray.wait(objectRefs, /*num_returns=*/ 1, /*timeoutMs=*/ 1000);
      System.out.println(waitResult.getReady()); // List of ready objects.
      System.out.println(waitResult.getUnready()); // list of unready objects.
    }
  
    // A regular Java class.
    public static class Counter {
  
      private int value = 0;
  
      public int increment() {
        this.value += 1;
        return this.value;
      }
    }
  
    public static void demoActors() {
      // Create an actor from this class.
      // `Ray.actor` takes a factory method that can produce
      // a `Counter` object. Here, we pass `Counter`'s constructor
      // as the argument.
      ActorHandle<Counter> counter = Ray.actor(Counter::new).remote();
  
      // Specify required resources for an actor.
      Ray.actor(Counter::new).setResource("CPU", 2.0).setResource("GPU", 0.5).remote();
  
      // Call the actor.
      ObjectRef<Integer> objectRef = counter.task(Counter::increment).remote();
      Assert.assertTrue(objectRef.get() == 1);
  
      // Create ten Counter actors.
      List<ActorHandle<Counter>> counters = new ArrayList<>();
      for (int i = 0; i < 10; i++) {
        counters.add(Ray.actor(Counter::new).remote());
      }
  
      // Increment each Counter once and get the results. These tasks all happen in
      // parallel.
      List<ObjectRef<Integer>> objectRefs = new ArrayList<>();
      for (ActorHandle<Counter> counterActor : counters) {
        objectRefs.add(counterActor.task(Counter::increment).remote());
      }
      // prints [1, 1, 1, 1, 1, 1, 1, 1, 1, 1]
      System.out.println(Ray.get(objectRefs));
  
      // Increment the first Counter five times. These tasks are executed serially
      // and share state.
      objectRefs = new ArrayList<>();
      for (int i = 0; i < 5; i++) {
        objectRefs.add(counters.get(0).task(Counter::increment).remote());
      }
      // prints [2, 3, 4, 5, 6]
      System.out.println(Ray.get(objectRefs));
    }
  
    public static void main(String[] args) {
      // Start Ray runtime. If you're connecting to an existing cluster, you can set
      // the `-Dray.address=<cluster-address>` java system property.
      Ray.init();
  
      demoTasks();
  
      demoObjects();
  
      demoActors();
    }
  }
  