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在多U程q发~程中，有时候会遇到大d分解成小d再ƈ发执行的场景?a title="Java 知识? target="_blank" style="color: #df3434; text-decoration: none; font-weight: bold;">Java 8新增的ForkJoinPool很好的支持了q个问题?/span>
ForkJoinPool是一U支持Q务分解的U程池，当提交给他的d“q大”Q他׃按照预先定义的规则将大Q务分解成Q务，多线Eƈ发执行?/span>
一般要配合可分解Q务接口ForkJoinTask来用，ForkJoinTask有两个实现它的抽象类QRecursiveAction和RecursiveTaskQ其区别是前者没有返回|后者有q回倹{?/span>
下面通过具体代码Q来C两个问题Q（1Q怎么定义可分解的dc?Q?Q如何用ForkJoinPool
package demo.thread.fork;
import java.util.Random;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.Future;
import java.util.concurrent.RecursiveTask;
public class ForkJoinPoolDemo {
public static void main(String[] args) throws InterruptedException, ExecutionException {
int arr[] = new int[100];
Random random = new Random();
int total = 0;
// 初始?00个数字元?/p>
for (int i = 0; i < arr.length; i++) {
int temp = random.nextInt(100);
// Ҏl元素赋?q将数组元素的值添加到totald?/p>
total += (arr[i] = temp);
}
System.out.println("初始化时的d=" + total);
// 创徏包含Runtime.getRuntime().availableProcessors()q回gZ数的q行U程的ForkJoinPool
ForkJoinPool forkJoinPool = new ForkJoinPool();
// 提交可分解的PrintTaskd
Future<Integer> future = forkJoinPool.submit(new SumTaskDemo(arr, 0,
arr.length));
System.out.println("计算出来的d=" + future.get());
// 关闭U程?/p>
forkJoinPool.shutdown();
}
}
// RecursiveTask为ForkJoinTask的抽象子c，有返回值的d
class SumTaskDemo extends RecursiveTask<Integer> {
private static final long serialVersionUID = 4033241174438751063L;
// 每个"Q?最多只打印20个数
private static final int MAX = 20;
private int arr[];
private int start;
private int end;
SumTaskDemo(int arr[], int start, int end) {
this.arr = arr;
this.start = start;
this.end = end;
}
@Override
protected Integer compute() {
int sum = 0;
// 当end-start的值小于MAX时候，开始打?/p>
if ((end - start) <= MAX) {
for (int i = start; i < end; i++) {
sum += arr[i];
}
return sum;
} else {
System.err.println("=====d分解======");
// 大d分解成两个小d
int middle = (start + end) >>>1;
SumTaskDemo left = new SumTaskDemo(arr, start, middle);
SumTaskDemo right = new SumTaskDemo(arr, middle, end);
// q行执行两个Q?/p>
left.fork();
right.fork();
// 把两个小d累加的结果合qv?/p>
return left.join() + right.join();
}
}
}
例子二：
package demo.thread.fork;
import java.util.Random;
import java.util.concurrent.ForkJoinPool;
import java.util.concurrent.RecursiveAction;
import java.util.concurrent.TimeUnit;
/**
* @author lin
*
*/
public class ForkJoinPoolDemo2 {
public static void main(String[] args) throws Exception {
// 创徏一个支持分解Q务的U程池ForkJoinPool
ForkJoinPool pool = new ForkJoinPool(4);
myTask task = new myTask(60);
pool.submit(task);
pool.awaitTermination(10, TimeUnit.SECONDS);// {待20sQ观察结?/p>
pool.shutdown();
}
}
/**
* 定义一个可分解的的dc，l承了RecursiveAction抽象c?必须实现它的computeҎ
*/
class myTask extends RecursiveAction {
private static final long serialVersionUID = 1L;
// 定义一个分解Q务的阈?#8212;—50,即一个Q务最多承?0个工作量
int THRESHOLD = 20;
// d?/p>
int task_Num = 0;
myTask(int Num) {
this.task_Num = Num;
}
@Override
protected void compute() {
if (task_Num <= THRESHOLD) {
System.out.println(Thread.currentThread().getName() + "承担?
+ task_Num + "份工?);
/*try {
Thread.sleep(1000);
} catch (InterruptedException e) {
e.printStackTrace();
}*/
} else {
// 随机解成两个d
Random m = new Random();
int x = m.nextInt(50);
myTask left = new myTask(x);
myTask right = new myTask(task_Num - x);
left.fork();
right.fork();
}
}
}
]]>
公式Q?br />
上面的太复杂Q来个简单的Q?br />
使用JAVA求实际利?/p>
Java代码 
- /**
- * 实际利率?/span>
- * @author Bean(mailto:mailxbs@126.com)
- * @param a 现?/span>
- * @param b q金
- * @param c 期数
- * @param cnt q算ơ数
- * @param ina 误差位数
- * @return 利率
- */
- public static double rate(double a,double b,double c,int cnt,int ina){
- double rate = 1,x,jd = 0.1,side = 0.1,i = 1;
- do{
- x = a/b - (Math.pow(1+rate, c)-1)/(Math.pow(rate+1, c)*rate);
- if(x*side>0){side = -side;jd *=10;}
- rate += side/jd;
- }while(i++<cnt&&Math.abs(x)>=1/Math.pow(10, ina));
- if(i>cnt)return Double.NaN;
- return rate;
- }
- public static void main(String agrs[]) {
- {
- Double 现?nbsp;= 7944760.00d;
- Double q金 = 186627.21d;
- Double 期数 = 48d;
- //计算200ơ，比Excel20ơ要_Q误差精到数点后10?/span>
- System.out.println(rate(现?q金,期数,200,10));
- }
- }
]]>
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3、在你安装Myeclipe的目录中Common\plugins\com.genuitec.eclipse.core_9.0.0.me201103181703.jarQ?br />用压~工h开QWinRAR?-zipQ我用的是WinMountQ再到com\genuitec\eclipse\core目录下，
替换publicKey.bytes文gQ?如图
4、修改ini配置文g。在MyEclipse 9.0\myeclipse.iniQ用C本开开Myeclipse.iniQ在最后加上下面两?/span>
![Myeclipse Enterprise Workbench 9.0破解Ҏ - leruge - 大学生刘? src=]()
5、打开MyeclipseQ在“preferences”Q即参数选择中）扑ֈ如图所C?/span>
7、随便写一个用户名Q我的是lerugeQ，点击下面两个按钮Q将生成的东西写上就行了?/span>
![Myeclipse Enterprise Workbench 9.0破解Ҏ - leruge - 大学生刘? src=]()
-Dgenuitec.honorDevMode=true
-Dosgi.dev=true
7、随便写一个用户名Q我的是lerugeQ，点击下面两个按钮Q将生成的东西写上就行了?/span>
8、到此Myeclipse Enterprise Workbench 9.0破解完毕?/span>
装：http://leruge.blog.163.com/blog/static/166845995201192474724627/
装：http://leruge.blog.163.com/blog/static/166845995201192474724627/
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