Future<Integer> result = executor.submit(task); //有返回值
  executor.executor(task)  //沒有返回值

public class Test {
    public static void main(String[] args) {
        ExecutorService executor = Executors.newCachedThreadPool();
        Task task = new Task();
        Future<Integer> result = executor.submit(task);
        executor.shutdown();
         
        try {
            Thread.sleep(1000);
        } catch (InterruptedException e1) {
            e1.printStackTrace();
        }
         
        System.out.println("主線程在執(zhí)行任務");
         
        try {
            System.out.println("task運行結(jié)果"+result.get());
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (ExecutionException e) {
            e.printStackTrace();
        } 
        System.out.println("所有任務執(zhí)行完畢");
    }
}
class Task implements Callable<Integer>{
    @Override
    public Integer call() throws Exception {
        System.out.println("子線程在進行計算");
        Thread.sleep(3000);
        int sum = 0;
        for(int i=0;i<100;i++)
            sum += i;
        return sum;
    }
}

public void run() {
   // 如果狀態(tài)不是 NEW，說明任務已經(jīng)執(zhí)行過或者已經(jīng)被取消，直接返回
   // 如果狀態(tài)是 NEW，則嘗試把執(zhí)行線程保存在 runnerOffset（runner字段），如果賦值失敗，則直接返回
    if (state != NEW ||
        !UNSAFE.compareAndSwapObject(this, runnerOffset,
                                     null, Thread.currentThread()))
        return;
    try {
       // 獲取構(gòu)造函數(shù)傳入的 Callable 值
        Callable<V> c = callable;
        if (c != null && state == NEW) {
            V result;
            boolean ran;
            try {
               // 正常調(diào)用 Callable 的 call 方法就可以獲取到返回值
                result = c.call();
                ran = true;
            } catch (Throwable ex) {
                result = null;
                ran = false;
               // 保存 call 方法拋出的異常
                setException(ex);
            }
            if (ran)
               // 保存 call 方法的執(zhí)行結(jié)果
                set(result);
        }
    } finally {        
        runner = null;       
        int s = state;
       // 如果任務被中斷，則執(zhí)行中斷處理
        if (s >= INTERRUPTING)
            handlePossibleCancellationInterrupt(s);
    }
}

** The result to return or exception to throw from get() */
private Object outcome; // non-volatile, protected by state reads/writes

// 保存異常結(jié)果
protected void setException(Throwable t) {
    if (UNSAFE.compareAndSwapInt(this, stateOffset, NEW, COMPLETING)) {
        outcome = t;
        UNSAFE.putOrderedInt(this, stateOffset, EXCEPTIONAL); // final state
        finishCompletion();
    }
}

// 保存正常結(jié)果
protected void set(V v) {
  if (UNSAFE.compareAndSwapInt(this, stateOffset, NEW, COMPLETING)) {
    outcome = v;
    UNSAFE.putOrderedInt(this, stateOffset, NORMAL); // final state
    finishCompletion();
  }
}

private void finishCompletion() {
    // assert state > COMPLETING;
    for (WaitNode q; (q = waiters) != null;) {
        if (UNSAFE.compareAndSwapObject(this, waitersOffset, q, null)) {
            for (;;) {
                Thread t = q.thread;
                if (t != null) {
                    q.thread = null;
                   // 喚醒等待隊列中的線程
                    LockSupport.unpark(t);
                }
                WaitNode next = q.next;
                if (next == null)
                    break;
                q.next = null; // unlink to help gc
                q = next;
            }
            break;
        }
    }

    done();

    callable = null;        // to reduce footprint
}  

public V get() throws InterruptedException, ExecutionException {
    int s = state;
   // 如果 state 還沒到 set outcome 結(jié)果的時候，則調(diào)用 awaitDone() 方法阻塞自己
    if (s <= COMPLETING)
        s = awaitDone(false, 0L);
   // 返回結(jié)果
    return report(s);
}

// get 方法支持超時限制，如果沒有傳入超時時間，則接受的參數(shù)是 false 和 0L
// 有等待就會有隊列排隊或者可響應中斷，從方法簽名上看有 InterruptedException，說明該方法這是可以被中斷的
private int awaitDone(boolean timed, long nanos)
    throws InterruptedException {
   // 計算等待截止時間
    final long deadline = timed ? System.nanoTime() + nanos : 0L;
    WaitNode q = null;
    boolean queued = false;
    for (;;) {
       // 如果當前線程被中斷，如果是，則在等待對立中刪除該節(jié)點，并拋出 InterruptedException
        if (Thread.interrupted()) {
            removeWaiter(q);
            throw new InterruptedException();
        }

        int s = state;
       // 狀態(tài)大于 COMPLETING 說明已經(jīng)達到某個最終狀態(tài)（正常結(jié)束/異常結(jié)束/取消）
       // 把 thread 只為空，并返回結(jié)果
        if (s > COMPLETING) {
            if (q != null)
                q.thread = null;
            return s;
        }
       // 如果是COMPLETING 狀態(tài)（中間狀態(tài)），表示任務已結(jié)束，但 outcome 賦值還沒結(jié)束，這時主動讓出執(zhí)行權(quán)，讓其他線程優(yōu)先執(zhí)行（只是發(fā)出這個信號，至于是否別的線程執(zhí)行一定會執(zhí)行可是不一定的）
        else if (s == COMPLETING) // cannot time out yet
            Thread.yield();
       // 等待節(jié)點為空
        else if (q == null)
           // 將當前線程構(gòu)造節(jié)點
            q = new WaitNode();
       // 如果還沒有入隊列，則把當前節(jié)點加入waiters首節(jié)點并替換原來waiters
        else if (!queued)
            queued = UNSAFE.compareAndSwapObject(this, waitersOffset,
                                                 q.next = waiters, q);
       // 如果設置超時時間
        else if (timed) {
            nanos = deadline - System.nanoTime();
           // 時間到，則不再等待結(jié)果
            if (nanos <= 0L) {
                removeWaiter(q);
                return state;
            }
           // 阻塞等待特定時間
            LockSupport.parkNanos(this, nanos);
        }
        else
           // 掛起當前線程，知道被其他線程喚醒
            LockSupport.park(this);
    }
}

public boolean cancel(boolean mayInterruptIfRunning) {
  
    if (!(state == NEW &&
          UNSAFE.compareAndSwapInt(this, stateOffset, NEW,
              mayInterruptIfRunning ? INTERRUPTING : CANCELLED)))
        return false;
    try {    // in case call to interrupt throws exception
       // 需要中斷任務執(zhí)行線程
        if (mayInterruptIfRunning) {
            try {
                Thread t = runner;
               // 中斷線程
                if (t != null)
                    t.interrupt();
            } finally { // final state
               // 修改為最終狀態(tài) INTERRUPTED
                UNSAFE.putOrderedInt(this, stateOffset, INTERRUPTED);
            }
        }
    } finally {
       // 喚醒等待中的線程
        finishCompletion();
    }
    return true;
}