Callable、Future和FutureTask
阿新 • • 發佈:2021-10-30
Callable
- Runnable沒有返回值:public abstract void run();,Callable可以有返回值:V call() throws Exception;
- 可以丟擲異常
- 方法不同,run()/call()
- 原始碼
public interface Callable<V> { /** * Computes a result, or throws an exception if unable to do so. * * @return computed result * @throws Exception if unable to compute a result */ V call() throws Exception; }
Future
- Future只是一個介面
- 能判斷任務是否完成;能夠中斷任務;能夠獲取任務執行結果。
- 原始碼
public interface Future<V> { // 如果取消已經完成的任務會返回false;如果任務正在執行,若mayInterruptIfRunning設定為true,則返回true,若mayInterruptIfRunning設定為false,則返回false;如果任務還沒有執行,則無論mayInterruptIfRunning為true還是false,肯定返回true。 boolean cancel(boolean mayInterruptIfRunning); // 是否被取消成功 boolean isCancelled(); // 是否已經完成 boolean isDone(); // 獲取執行結果,這個方法會產生阻塞,會一直等到任務執行完畢才返回 V get() throws InterruptedException, ExecutionException; // 如果在指定時間內,還沒獲取到結果,就直接返回null V get(long timeout, TimeUnit unit) throws InterruptedException, ExecutionException, TimeoutException; }
FutureTask
-
FutureTask是Future介面的一個唯一實現類
-
繼承關係
public interface RunnableFuture<V> extends Runnable, Future<V> {
void run();
}
public class FutureTask<V> implements RunnableFuture<V>
RunnableFuture繼承了Runnable介面和Future介面,而FutureTask實現了RunnableFuture介面。所以它既可以作為Runnable被執行緒執行,又可以作為Future得到Callable的返回值。
- 構造方法
public FutureTask(Callable<V> callable) {
if (callable == null)
throw new NullPointerException();
this.callable = callable;
this.state = NEW;
}
public FutureTask(Runnable runnable, V result) {
this.callable = Executors.callable(runnable, result);
this.state = NEW;
}
- Callable+Future
import java.util.concurrent.*;
class MyCallable {
public static void main(String[] args) throws InterruptedException {
ExecutorService executor = Executors.newCachedThreadPool();
Task task = new Task();
Future<Integer> result = executor.submit(task);
executor.shutdown();
TimeUnit.SECONDS.sleep(1);
System.out.println("主執行緒在執行任務");
try {
System.out.println("task執行結果" + result.get());
} catch (InterruptedException | ExecutionException e) {
e.printStackTrace();
}
System.out.println("所有任務執行完畢");
}
}
class Task implements Callable<Integer> {
@Override
public Integer call() throws Exception {
System.out.println("子執行緒在進行計算");
TimeUnit.SECONDS.sleep(2);
int sum = 0;
for (int i = 0; i < 100; i++)
sum += i;
return sum;
}
}
- Callable+FutureTask
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.FutureTask;
class MyCallable {
public static void main(String[] args) throws ExecutionException, InterruptedException {
// new Thread(new Runnable()).start();
// new Thread(new FutureTask<V>()).start();
// new Thread(new FutureTask<V>( Callable )).start();
MyThread myThread = new MyThread();
FutureTask<Integer> integerFutureTask = new FutureTask<>(myThread); // 適配類
new Thread(integerFutureTask, "A").start();
new Thread(integerFutureTask, "B").start(); // 結果會被快取,只會列印一個call
Integer o = integerFutureTask.get(); // 返回值 此方法可能會產生阻塞,最好放在最後一行
System.out.println(o);
}
}
class MyThread implements Callable<Integer> {
@Override
public Integer call() throws Exception {
System.out.println("call()");
return 7;
}
}