Concurrency Knowledge #1

concurrency_programing

package main;
import java.util.ArrayList;
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 ExecutorTest {
    public static void main(String[] args) {
        // different executor types:
        ExecutorService execCached = Executors.newCachedThreadPool();
        ExecutorService execFixed = Executors.newFixedThreadPool(5);
        ExecutorService execSingle = Executors.newSingleThreadExecutor();
        // execute runnable object
        //for (int i = 0; i < 5; i++)
        // execCached.execute(new ExecRunObject(5));
        // execFixed.execute(new ExecRunObject(5));
        // execSingle.execute(new ExecRunObject(5));
        //execCached.shutdown();
        /** The following example is for callable interface implementation **/
        ExecutorService execCall = Executors.newCachedThreadPool();
        // exec submit produce Future object
        ArrayList<Future<String>> res = new ArrayList<Future<String>>();
        for (int i = 0; i < 5; i++)
            res.add(execCall.submit(new ExecCallObject(i)));
        for (Future f : res)
            try {
                System.out.println(f.get());
            } catch (InterruptedException e) {
                e.printStackTrace();
            } catch (ExecutionException e) {
                e.printStackTrace();
            }finally{
                execCall.shutdown();
            }
    }
}
// implements runnable interface
class ExecRunObject implements Runnable {
    protected int countDown = 10;
    private static int taskCount = 0;
    private final int id = taskCount++;
    public ExecRunObject(int countDown) {
        this.countDown = countDown;
    }
    public String status() {
        return "#" + id + "(" + (countDown > 0 ? countDown : "LiftOff") + ")";
    }
    @Override
    public void run() {
        while (countDown-- > 0) {
            System.out.print(status());
            Thread.yield();
        }
    }
}
// implements callable interface, in order to acquire return value from tasks
class ExecCallObject implements Callable<String> {
    private int id;
    public ExecCallObject(int id) {
        this.id = id;
    }
    @Override
    public String call() throws Exception {
        // TODO Auto-generated method stub
        return "result of Task" + id;
    }
}