在 java 中并行执行 for 循环

Question

我在java中使用了ExecutorService和FutureTask在for循环中执行并行操作。以下是代码

package com.sample.threading.parallel;
import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.FutureTask;
public class Combinations { 
   public static String[] fillArray(int range) {
        String a[] = new String[100];
        for (int i = ((10 * range) + 1); i < (10 * (range + 1)); i++) {
            a[i] = "Name " + i;
        }
        return a;
    }

    public static String[] futureFillArray() throws Exception {
        String a[] = new String[100];
        int threadNum = 2;
        ExecutorService executor = Executors.newFixedThreadPool(threadNum);
        List<FutureTask<String[]>> taskList = new ArrayList<FutureTask<String[]>>();
        FutureTask<String[]> futureTask = new FutureTask<String[]>(
                new Callable<String[]>() {
                    @Override
                    public String[] call() throws Exception {
                        return fillArray(0);
                    }
                });
        taskList.add(futureTask);
        executor.execute(futureTask);
        FutureTask<String[]> futureTask1 = new FutureTask<String[]>(
                new Callable<String[]>() {
                    @Override
                    public String[] call() throws Exception {
                        return fillArray(1);
                    }
                });
        taskList.add(futureTask1);
        executor.execute(futureTask1);
        FutureTask<String[]> futureTask2 = new FutureTask<String[]>(
                new Callable<String[]>() {
                    @Override
                    public String[] call() throws Exception {
                        return fillArray(2);
                    }
                });
        taskList.add(futureTask2);
        executor.execute(futureTask2);
        FutureTask<String[]> futureTask3 = new FutureTask<String[]>(
                new Callable<String[]>() {
                    @Override
                    public String[] call() throws Exception {
                        return fillArray(3);
                    }
                });
        taskList.add(futureTask3);
        executor.execute(futureTask3);
        for (int j = 0; j < threadNum; j++) {
            FutureTask<String[]> futureTaskF = taskList.get(j);
            a = futureTaskF.get();
        }
        executor.shutdown();
        return a;
    }
}

我知道我必须调用 fillArray 方法10 次，但我只调用了 3 次。以下是执行类

package com.sample.threading.parallel;
import java.util.Calendar;
public class ExecuteCombinations {
    public static void main(String[] args) throws Exception {
         long timeStart = Calendar.getInstance().getTimeInMillis();
            String res[] = Combinations.fillArray(0);
            long timeEnd = Calendar.getInstance().getTimeInMillis();
            long timeNeeded = timeEnd - timeStart;
            System.out.println("Result         : " + res + " calculated in " + timeNeeded + " ms");
            // Parallel execution
            long timeStartFuture = Calendar.getInstance().getTimeInMillis();
            String res2[] = Combinations.futureFillArray();
            long timeEndFuture = Calendar.getInstance().getTimeInMillis();
            long timeNeededFuture = timeEndFuture - timeStartFuture;
            System.out.println("Result (Future): " + res2 + " calculated in " + timeNeededFuture + " ms");
    }
}

但仍然是输出

Result         : [Ljava.lang.String;@773d3f62 calculated in 0 ms
Result (Future): [Ljava.lang.String;@47b6617 calculated in 16 ms

我的实现有误吗？请告知

Answer 1

我不确定我是否正确理解了你。你想知道为什么尽管运行 3 个期货，你只得到两行输出，对吧？如果是这种情况，您只需调整String res2[] = Combinations.futureFillArray();的打印（即使用 for 循环迭代res2[]中的所有条目即可查看所有结果。