Java中的可调用和未来
java.util.concurrent。与只能运行线程的可运行接口相反，可调用对象可以返回线程完成的计算结果。Callable对象返回一个Future对象，该对象提供方法来监视线程正在执行的任务的进度。将来的对象可用于检查Callable的状态，然后在线程完成后从Callable检索结果。它还提供了超时功能。
语法
//submit the callable using ThreadExecutor //and get the result as a Future object Future<Long> result10 = executor.submit(new FactorialService(10)); //get the result using get method of the Future object //get method waits till the thread execution and then return the result of the execution. Long factorial10 = result10.get();
示例
下面的TestThread程序显示了在基于线程的环境中Future和Callables的用法。
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 TestThread {
public static void main(final String[] arguments) throws InterruptedException, ExecutionException {
ExecutorService executor = Executors.newSingleThreadExecutor();
System.out.println("Factorial Service called for 10!");
Future<Long> result10 = executor.submit(new FactorialService(10));
System.out.println("Factorial Service called for 20!");
Future<Long> result20 = executor.submit(new FactorialService(20));
Long factorial10 = result10.get();
System.out.println("10! = " + factorial10);
Long factorial20 = result20.get();
System.out.println("20! = " + factorial20);
executor.shutdown();
}
static class FactorialService implements Callable<Long> {
private int number;
public FactorialService(int number) {
this.number = number;
}
@Override
public Long call() throws Exception {
return factorial();
}
private Long factorial() throws InterruptedException {
long result = 1;
while (number != 0) {
result = number * result;
number--;
Thread.sleep(100);
}
return result;
}
}
}这将产生以下结果。
输出结果
Factorial Service called for 10! Factorial Service called for 20! 10! = 3628800 20! = 2432902008176640000