java中Callable接口是使用示例

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与Runnable区别：

        Runnable：没有返回信息，实现run()方法。

        Callable<T>： A task that returns a result and may throw an exception ，返回执行结果，抛出异常；需要实现call()方法

Future

        Future就是对于具体的Runnable或者Callable任务的执行结果进行取消、查询是否完成、获取结果、设置结果操作。get方法会阻塞，直到任务返回结果。

FutureTask

         FutureTask实现了Runnbale又实现了Futrue<V>这两个接口，既是Future、Runnable，又包装了Callable。

eg:

import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import java.util.concurrent.Callable;
import java.util.concurrent.CompletionService;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorCompletionService;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;
import java.util.concurrent.FutureTask;

public class CallableTest{

public static void main(String[] args) throws InterruptedException, ExecutionException {

//1 。因此FutureTask既是Future、 Runnable，又是包装了Callable( 如果是Runnable最终也会被转换为Callable )， 它是这两者的合体。
FutureTask<Integer> futureTask = new FutureTask<>(new Callable<Integer>() {
@Override
public Integer call() throws Exception {
return new Random().nextInt(100);
}
});
new Thread(futureTask).start();
System.out.println(futureTask.get());
System.out.println("###########################################################");

//2 Executor就是Runnable和Callable的调度容器，Future就是对于具体的Runnable或者Callable任务的执行结果进行取消、查询是否完成、获取结果、设置结果操作
ExecutorService threadPool = Executors.newSingleThreadExecutor();
Future<Integer> future = threadPool.submit(new Callable<Integer>() {
@Override
public Integer call() throws Exception {
return new Random().nextInt(100);
}
});
//get方法会阻塞，直到任务返回结果
System.out.println(future.get());
System.out.println("###########################################################");

//3 Future是按照添加的顺序排列的
ExecutorService threadPool1 = Executors.newSingleThreadExecutor();
List<Future<Integer>> list = new ArrayList<>();
for(int i=0;i<5;i++){
list.add(threadPool1.submit(new Callable<Integer>() {
@Override
public Integer call() throws Exception {
return new Random().nextInt(100);
}
}));
}
for(Future<Integer> fs:list){
System.out.println(fs.get());
}
System.out.println("------------------------");

ArrayList<Callable<Integer>> arrayList = new ArrayList<Callable<Integer>>();
for(int i=0;i<5;i++){
arrayList.add(new Callable<Integer>() {
@Override
public Integer call() throws Exception {
return new Random().nextInt(100);
}
});
}
List<Future<Integer>> result = threadPool1.invokeAll(arrayList);
for(Future<Integer> fs:result){
System.out.println(fs.get());
}
System.out.println("###########################################################");

//4  提交到CompletionService中的Future是按照完成的顺序排列的
ExecutorService executorService = Executors.newSingleThreadExecutor();
CompletionService<Integer> cs = new ExecutorCompletionService<>(executorService);
for(int i=0;i<5;i++){
final int id = i;
cs.submit(new Callable<Integer>() {
@Override
public Integer call() throws Exception {
return id;
}
});
}
for(int i=0;i<5;i++){
System.out.println(cs.take().get());
}
System.out.println("###########################################################");

}
}