java 多线程Callable和Runable执行顺序问题详解
详见： http://blog.yemou.net/article/query/info/tytfjhfascvhzxcyt125
毫无疑问 Runnable会进行异步执行，此处不多数，主要说明Callable的使用，看实例：
1、
public class ThreadTest {
public static void main(String[] args) throws InterruptedException, ExecutionException {
ExecutorService executor = Executors.newFixedThreadPool(4);
MyTread m1 = new MyTread();
Future f = executor.submit(m1);
// System.out.println(f.get());
executor.shutdown();
System.out.println("akb");
}
}
class MyTread implements Callable<String> {
@Override
public String call() {
try {
System.out.println("线程调度：" + Thread.currentThread());
TimeUnit.SECONDS.sleep(3);
} catch (InterruptedException e) {
e.printStackTrace();
}
return "123";
}
}
此程序虽然获取了call方法的返回值，但是没有做处理，所以主线程main和m1同时执行，执行结果如下：
主线程执行完了
线程调度：Thread[pool-1-thread-1,5,main]
2、
public class ThreadTest {
public static void main(String[] args) throws InterruptedException, ExecutionException {
ExecutorService executor = Executors.newFixedThreadPool(4);
MyTread m1 = new MyTread();
Future f = executor.submit(m1);
System.out.println(f.get()); // 进行了输出
executor.shutdown();
System.out.println("主线程执行完了");
}
}
class MyTread implements Callable<String> {
@Override
public String call() {
try {
System.out.println("线程调度：" + Thread.currentThread());
TimeUnit.SECONDS.sleep(3);
} catch (InterruptedException e) {
e.printStackTrace();
}
return "123";
}
}
在2中，对m1中call方法的返回值在main中进行了处理（输出），所以在此种情况下，main需要等待m1执行完，再继续执行，执行结果如下
线程调度：Thread[pool-1-thread-1,5,main]
123
主线程执行完了
3、再看当主线程中同时启动两个由Callable生成的线程时
public class ThreadTest {
public static void main(String[] args) throws InterruptedException, ExecutionException {
ExecutorService executor = Executors.newFixedThreadPool(4);
MyTread m1 = new MyTread();
MyTread2 m2 = new MyTread2();
Long time1 = TimeUnit.MILLISECONDS.toSeconds(System.currentTimeMillis());
Future f = executor.submit(m1);
Future f2 = executor.submit(m2);
System.out.println(f.get()); // 进行了输出m1
System.out.println(f2.get()); // 进行了输出m2
executor.shutdown();
System.out.println("主线程执行完了");
Long time2 = TimeUnit.MILLISECONDS.toSeconds(System.currentTimeMillis());
System.out.println("主线程等待了" + (time2 - time1) + "秒");
}
}
class MyTread implements Callable<String> {
@Override
public String call() {
try {
System.out.println("线程调度：" + Thread.currentThread());
TimeUnit.SECONDS.sleep(3);
} catch (InterruptedException e) {
e.printStackTrace();
}
return "123";
}
}
class MyTread2 implements Callable<String> {
@Override
public String call() {
try {
System.out.println("线程调度2：" + Thread.currentThread());
TimeUnit.SECONDS.sleep(3);
} catch (InterruptedException e) {
e.printStackTrace();
}
return "abc";
}
}
当不对m1和m2做输出时，main和m1、m2并发执行，当对m1和m2中任意一个的返回值进行处理的时候，main需要等待，但是m1和m2之前仍然是并发执行，执行结果如下：
线程调度2：Thread[pool-1-thread-2,5,main]
线程调度：Thread[pool-1-thread-1,5,main]
123
abc
主线程执行完了
主线程等待了3秒