Java 中的 Callable 和 Future\
java programming java8object oriented programming更新于 2024/10/22 22:53:00
java.util.concurrent。与只能运行线程的 Runnable 接口不同，Callable 对象可以返回线程完成的计算结果。Callable 对象返回 Future 对象，该对象提供用于监视线程正在执行的任务进度的方法。future 对象可用于检查 Callable 的状态，然后在线程完成后从 Callable 中检索结果。它还提供超时功能。
语法
//使用 ThreadExecutor 提交可调用函数 //并以 Future 对象的形式获取结果 Future<Long> result10 = executor.submit(new FactorialService(10)); //使用 Future 对象的 get 方法获取结果 //get 方法等待线程执行，然后返回执行结果。 Long factorial10 = result10.get();
示例
以下 TestThread 程序展示了在基于线程的环境中 Futures 和 Callables 的使用。
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
Factorial Service called for 10! Factorial Service called for 20! 10! = 3628800 20! = 2432902008176640000
