Non Blocking Channel Operations in Karel

Java doesn’t have built-in channels like Go, so we’ll use BlockingQueue to simulate similar behavior. We’ll also use ExecutorService for concurrency.

import java.util.concurrent.*;

public class NonBlockingOperations {
    public static void main(String[] args) {
        BlockingQueue<String> messages = new LinkedBlockingQueue<>();
        BlockingQueue<Boolean> signals = new LinkedBlockingQueue<>();

        // Here's a non-blocking receive. If a value is
        // available in `messages` then it will be retrieved.
        // If not, it will immediately take the `else` case.
        String msg = messages.poll();
        if (msg != null) {
            System.out.println("received message " + msg);
        } else {
            System.out.println("no message received");
        }

        // A non-blocking send works similarly. Here `msg`
        // is offered to the `messages` queue. If the queue
        // is full, the `offer` method will return false and
        // the `else` case will be executed.
        msg = "hi";
        if (messages.offer(msg)) {
            System.out.println("sent message " + msg);
        } else {
            System.out.println("no message sent");
        }

        // We can use multiple conditions to implement a multi-way
        // non-blocking select. Here we attempt non-blocking receives
        // on both `messages` and `signals`.
        String receivedMsg = messages.poll();
        Boolean receivedSignal = signals.poll();

        if (receivedMsg != null) {
            System.out.println("received message " + receivedMsg);
        } else if (receivedSignal != null) {
            System.out.println("received signal " + receivedSignal);
        } else {
            System.out.println("no activity");
        }
    }
}

To run the program:

$ javac NonBlockingOperations.java
$ java NonBlockingOperations
no message received
no message sent
no activity

In this Java version, we use BlockingQueue to simulate channels. The poll() method is used for non-blocking receives, and offer() for non-blocking sends. We use if-else statements to mimic the behavior of Go’s select with a default case.

Note that this is a simplified simulation and doesn’t capture all the nuances of Go’s channel operations. In a real-world scenario, you might need to use more sophisticated concurrency primitives or libraries depending on your specific requirements.

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Non Blocking Channel Operations in Karel