利用并發編程，實現計算大量數據的和

實現代碼：

package tj.pojo.generate.main;import java.util.ArrayList; import java.util.List; 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; import java.util.concurrent.FutureTask;public class ConcurrentCalculator {private ExecutorService exec;private int cpuCoreNumber;private List<Future<Long>> tasks = new ArrayList<Future<Long>>();// 內部類class SumCalculator implements Callable<Long> {private int[] numbers;private int start;private int end;public SumCalculator(final int[] numbers, int start, int end) {this.numbers = numbers;this.start = start;this.end = end;}@Overridepublic Long call() throws Exception {Long sum = 0L;for (int i = start; i < end; i++) {sum += numbers[i];}System.out.println(String.format("%s~%s的和為%s", start, end, sum));return sum;}}public ConcurrentCalculator() {cpuCoreNumber = Runtime.getRuntime().availableProcessors();System.out.println("CPU核心數：" + cpuCoreNumber);exec = Executors.newFixedThreadPool(cpuCoreNumber);}public Long sum(final int[] numbers) {for (int i = 0; i < cpuCoreNumber; i++) {int increment = numbers.length / cpuCoreNumber + 1;int start = increment * i;int end = start + increment;if (end > numbers.length) {end = numbers.length;}SumCalculator task = new SumCalculator(numbers, start, end);FutureTask<Long> future = new FutureTask<Long>(task);tasks.add(future);System.out.println("添加一個任務，總任務數為：" + tasks.size());if (!exec.isShutdown()) {exec.submit(future);// ExecutoreService提供了submit()方法，傳遞一個Callable，或Runnable，返回Future。// exec.submit(task); }}System.out.println("任務分配完成，總任務數為：" + tasks.size());return getResult();}public Long getResult() {Long sums = 0L;for (Future<Long> task : tasks) {try {Long sum = task.get();sums += sum;System.out.println("當前總合計：" + sums);} catch (InterruptedException e) {e.printStackTrace();} catch (ExecutionException e) {e.printStackTrace();}}return sums;}public void close() {exec.shutdown();} }

其中，在代碼的第62行~第64行，由于不了解ExecutoreService.submit(Runnable task)方法的功能。

同時FutureTask<Long> future和SumCalculator task都實現了Runnable接口，造成代碼調用時，進程一直不結束。

傳遞了FutureTask<Long> future才正確執行。

exec.submit(future);// ExecutoreService提供了submit()方法，傳遞一個Callable，或Runnable，返回Future。// exec.submit(task);

測試方法：

public static void test() {int[] numbers = new int[100];for (int i = 0; i < 100; i++) {numbers[i] = i + 1;}tj.pojo.generate.main.ConcurrentCalculator cc = new tj.pojo.generate.main.ConcurrentCalculator();Long sum = cc.sum(numbers);System.out.println("1~100的和為" + sum);cc.close();}

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FutureTask的實現代碼：

public class FutureTask<V> implements RunnableFuture<V>

FutureTask類實現了RunnableFuture接口，RunnableFuture接口的實現代碼：

public interface RunnableFuture<V> extends Runnable, Future<V> {

??? void run();

}

可以看出RunnableFuture繼承了Runnable接口和Future接口，而FutureTask實現了RunnableFuture接口。

所以它既可以作為Runnable被線程執行，又可以作為Future得到Callable的返回值。

事實上，FutureTask是Future接口的一個唯一實現類。

并發編程的兩種實現形式：

1)：使用Callable+Future獲取執行結果

public class Test {public static void main(String[] args) {ExecutorService executor = Executors.newCachedThreadPool();Task task = new Task();Future<Integer> result = executor.submit(task);executor.shutdown();try {Thread.sleep(1000);} catch (InterruptedException e1) {e1.printStackTrace();}System.out.println("主線程在執行任務");try {System.out.println("task運行結果"+result.get());} catch (InterruptedException e) {e.printStackTrace();} catch (ExecutionException e) {e.printStackTrace();}System.out.println("所有任務執行完畢");} } class Task implements Callable<Integer>{@Overridepublic Integer call() throws Exception {System.out.println("子線程在進行計算");Thread.sleep(3000);int sum = 0;for(int i=0;i<100;i++)sum += i;return sum;} }

2)：使用Callable+FutureTask獲取執行結果

public class Test {public static void main(String[] args) {//第一種方式ExecutorService executor = Executors.newCachedThreadPool();Task task = new Task();FutureTask<Integer> futureTask = new FutureTask<Integer>(task);executor.submit(futureTask);executor.shutdown();//第二種方式，注意這種方式和第一種方式效果是類似的，只不過一個使用的是ExecutorService，一個使用的是Thread/*Task task = new Task();FutureTask<Integer> futureTask = new FutureTask<Integer>(task);Thread thread = new Thread(futureTask);thread.start();*/try {Thread.sleep(1000);} catch (InterruptedException e1) {e1.printStackTrace();}System.out.println("主線程在執行任務");try {System.out.println("task運行結果"+futureTask.get());} catch (InterruptedException e) {e.printStackTrace();} catch (ExecutionException e) {e.printStackTrace();}System.out.println("所有任務執行完畢");} } class Task implements Callable<Integer>{@Overridepublic Integer call() throws Exception {System.out.println("子線程在進行計算");Thread.sleep(3000);int sum = 0;for(int i=0;i<100;i++)sum += i;return sum;} }

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轉載于:https://www.cnblogs.com/Candies/p/5692389.html

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