java 接收c 返回数据 java怎么接收返回值

java5之前是没有返回值的，Java5新增了Callable接口获得线程的返回值，用法如下：

package com.ronniewang;
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 GetReturnValueFromCallable {
private static final int SLEEP_MILLS = 3000;
private static final int SECOND_MILLS = 1000;
private static int sleepSeconds = SLEEP_MILLS / SECOND_MILLS;
ExecutorService executorService = Executors.newCachedThreadPool();
/**
* 在创建多线程程序的时候，我们常实现Runnable接口，Runnable没有返回值，要想获得返回值，Java5提供了一个新的接口Callable
*/
public static void main(String[] args) {
new GetReturnValueFromCallable().testCallable();
}
private void testCallable() {
/**
* Callable需要实现的是call()方法，而不是run()方法，返回值的类型有Callable的类型参数指定，
* Callable只能由ExecutorService.submit() 执行，正常结束后将返回一个future对象
*/
Future future = executorService.submit(new Callable() {
public String call() throws Exception {
Thread.sleep(SLEEP_MILLS);
return "I from callable";
}
});
while (true) {
/**
* 获得future对象之前可以使用isDone()方法检测future是否完成，完成后可以调用get()方法获得future的值，
* 如果直接调用get()方法，get()方法将阻塞值线程结束
*/
if (future.isDone()) {
try {
System.out.println(future.get());
break;
} catch (InterruptedException e) {
// ignored
} catch (ExecutionException e) {
 // ignored
}
}
else {
try {
System.out.println("after " + sleepSeconds-- + " seconds, we will get future");
Thread.sleep(SECOND_MILLS);
} catch (InterruptedException e) {
 // ignored
}
}
}
}
}