What can be called Java?

Question

The title pretty much sums it up.

I want to know the concept and idea of ​​the callee. I read here the question of the difference between called and executed. but do not show anyone the code and describe in detail what the called is. I do not want to know the difference between the two. I want to know,

• What is called called?

• When to use them and how to use them.

• When they come into action for Android.

Answer 1

You can check this example :

Callable , , . Executor 100 Future .

package com.journaldev.threads;

import java.util.ArrayList;
import java.util.Date;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;

public class MyCallable implements Callable<String> {

    @Override
    public String call() throws Exception {
        Thread.sleep(1000);
        //return the thread name executing this callable task
        return Thread.currentThread().getName();
    }

    public static void main(String args[]){
        //Get ExecutorService from Executors utility class, thread pool size is 10
        ExecutorService executor = Executors.newFixedThreadPool(10);
        //create a list to hold the Future object associated with Callable
        List<Future<String>> list = new ArrayList<Future<String>>();
        //Create MyCallable instance
        Callable<String> callable = new MyCallable();
        for(int i=0; i< 100; i++){
            //submit Callable tasks to be executed by thread pool
            Future<String> future = executor.submit(callable);
            //add Future to the list, we can get return value using Future
            list.add(future);
        }
        for(Future<String> fut : list){
            try {
                //print the return value of Future, notice the output delay in console
                // because Future.get() waits for task to get completed
                System.out.println(new Date()+ "::"+fut.get());
            } catch (InterruptedException | ExecutionException e) {
                e.printStackTrace();
            }
        }
        //shut down the executor service now
        executor.shutdown();
    }

}

Runnables

Answer 2

Callable Runnable, . , , .

Future.

, FutureTask ( RunnableFuture )

public static void main(String[] args) {

    // providing an anonymous callable to FutureTask
    RunnableFuture<String> future = new FutureTask<String>(
            new Callable<String>() {
                @Override
                public String call() throws InterruptedException {
                    System.out.println("sleeping");
                    Thread.sleep(2000);
                    System.out.println("returning");
                    return "hello-world";
                }

            });

    Thread t = new Thread(future);
    t.start();

    try {
        // the get Waits if necessary for the computation to complete
        System.out.println(future.get());
    } catch (InterruptedException | ExecutionException e) {
        e.printStackTrace();
    }

}