adding task to list stopping a task getting the result of a task

[oll3i]

 
import javax.swing.*;
import java.awt.event.*;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.*;
import java.lang.reflect.*;

public class Exec1 extends JFrame implements ActionListener {

  int k = 0;
  int n = 15;
  JTextArea ta = new JTextArea(40,20);
  List<Future> taskList= new ArrayList<Future>();
  Exec1() {
    add(new JScrollPane(ta));
    JPanel p = new JPanel();
    JButton b = new JButton("Start");
    b.addActionListener(this);
    p.add(b);
    b = new JButton("Stop current");
    b.setActionCommand("Stop");
    b.addActionListener(this);
    p.add(b);
    b = new JButton("Curent result");
    b.setActionCommand("Result");
    b.addActionListener(this);
    p.add(b);
    b = new JButton("Shutdown");
    b.addActionListener(this);
    p.add(b);
    b = new JButton("ShutdownNow");
    b.addActionListener(this);
    p.add(b);
    add(p, "South");
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    pack();
    setVisible(true);
  }

  public void actionPerformed(ActionEvent e)  {
    String cmd = e.getActionCommand();
    try {
      Method m = this.getClass().getDeclaredMethod("task"+cmd);
      m.invoke(this);
    } catch(Exception exc) { exc.printStackTrace(); }
  }


  class SumTask implements Callable<Integer> {

    private int taskNum,
                limit;

    public SumTask(int taskNum, int limit) {
      this.taskNum = taskNum;
      this.limit = limit;
    }

    public Integer call() throws Exception {
      int sum = 0;
      for (int i = 1; i <= limit; i++) {
        if (Thread.currentThread().isInterrupted()) return null;
        sum+=i;
        ta.append("Task " + taskNum + " part result = " + sum + '\n');
        Thread.sleep(1000);
      }
      return sum;
    }
  };

  Future<Integer> task;

  //ExecutorService exec = Executors.newSingleThreadExecutor();
  ExecutorService exec = Executors.newFixedThreadPool(3);

  public void taskStart() {
    try {
    	
      taskList.add(task);
      task = exec.submit(new SumTask(++k, 15));
    } catch(RejectedExecutionException exc) {
        ta.append("Execution rejected\n");
        return;
    }
    ta.append("Task " + k + " submitted\n");
  }

  public void taskResult() {
	  
	for(int i=0;i<taskList.size();i++){
	    task=taskList.get(i);
    String msg = "";
    if (task.isCancelled()) msg = "Task cancelled.";
    else if (task.isDone()) {
      try {
        msg = "Ready. Result = " + task.get();
      } catch(Exception exc) {
          msg = exc.getMessage();
      }
    }
    else msg = "Task is running or waiting for execution";
    JOptionPane.showMessageDialog(null, msg);
    }
  }

  public void taskStop() {
    task.cancel(true);
  }

  public void taskShutdown() {
    exec.shutdown();
    ta.append("Executor shutdown\n");
  }

  public void taskShutdownNow() {
    List<Runnable> awaiting = exec.shutdownNow();
    ta.append("Executor shutdown now - awaiting tasks:\n");
    for (Runnable r : awaiting) {
      ta.append(r.getClass().getName()+'\n');
    }

 }


  public static void main(String[] args) {
     new Exec1();
  }

}

i want to add tasks to a list then when a button is clicked stop a task or when another button is clicked show result of a task
when eg taskResult() is called i need to find that task(eg first task) in a list then show the result i dont want to limit the number of tasks(i cd do that with buttons) but i want to have unlimited number of tasks
but how i can get the result of eg 1st task then the second task etc.?
is it possible ? any hints ?
thank you in advance