Java使用5個線程計算數(shù)組之和

更新時間：2021年05月20日 11:00:02 作者：安迪爸爸

本文主要介紹了Java使用5個線程計算數(shù)組之和，對大家的學(xué)習(xí)或者工作具有一定的參考學(xué)習(xí)價值，需要的朋友們下面隨著小編來一起學(xué)習(xí)學(xué)習(xí)吧

前言

之前寫過多線程累加計數(shù)，原理跟本篇類似，傳送門

累加計數(shù)比計算數(shù)組之和邏輯稍微簡單一點(diǎn)，如果對于這塊不熟悉的，可以先看下累加計數(shù)。

基本思想已經(jīng)在之前那篇文章里寫過了，這里就直接貼代碼了。

這里分別通過自己創(chuàng)建線程來實(shí)現(xiàn)功能，還有通過線程池來實(shí)現(xiàn)功能。思想都差不多。只是代碼寫法略有不同。僅供參考。

代碼一：

五個線程交替累加計算數(shù)組之和，這種方法其實(shí)不如單線程直接累加快，因?yàn)榻惶胬奂有枰耙粋€線程計算的結(jié)果。

package test;
 
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
 
public class FiveThreadCount {
 private int count=0;
 private int[] arr={1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28};
 private int j=0;
 //定義一個任務(wù)，關(guān)鍵點(diǎn)所在
 private class MyThread extends Thread{
  @Override
  public void run() {
   super.run();
    while(j<arr.length)
    {
     synchronized (MyThread.class) {
      if(j>=arr.length){
       return;
      }
      count+=arr[j++];
      try {
       Thread.sleep(100);
      } catch (InterruptedException e) {
       // TODO Auto-generated catch block
       e.printStackTrace();
      }
      System.out.println(Thread.currentThread().getName());
     }
    }
  }
 }
 
 //方法一
 public void test1(){
  for(int i=0;i<5;i++){
   new MyThread().start();
  }
        try {
   Thread.sleep(10000);
  } catch (InterruptedException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  }
        System.out.println(count);
 }
 //方法二
 public void test2(){
  Thread myThread=new MyThread();
  for(int i=0;i<5;i++){
   new Thread(myThread).start();
  }
        try {
   Thread.sleep(10000);
  } catch (InterruptedException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  }
        System.out.println(count);
 }
 //方法一的線程池實(shí)現(xiàn)版
 public void test3(){
  ExecutorService service=Executors.newCachedThreadPool();
  for(int i=0;i<5;i++){
   service.execute(new MyThread());
  }
        try {
   Thread.sleep(10000);
  } catch (InterruptedException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  }
        System.out.println(count);
 }
 //方法二的線程池實(shí)現(xiàn)版
 public void test4(){
  ExecutorService service=Executors.newCachedThreadPool();
  Thread myThread=new MyThread();
  for(int i=0;i<5;i++){
   service.execute(myThread);
  }
        try {
   Thread.sleep(10000);
  } catch (InterruptedException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  }
        System.out.println(count);
 }
 
}

上邊代碼中，用到了sleep方法的原因，sleep(100)是為了讓其他線程有時間執(zhí)行任務(wù)，如果不sleep的話，有可能一個線程就全部執(zhí)行完了。最后的sleep（10000）是為了等所有線程執(zhí)行完后，打印最后的計算結(jié)果。

代碼二：

將數(shù)組分為5等分，讓每個線程計算自己負(fù)責(zé)的那份，并發(fā)計算，最后匯總結(jié)果。這種方式比代碼一速度會快些。因?yàn)榫€程獨(dú)立計算，不依賴其他線程的結(jié)果。最后幾個線程將總數(shù)累加即可。

方式一：

使用Callable，F(xiàn)utureTask方式，來實(shí)現(xiàn)代碼：

package test;
 
import java.util.concurrent.Callable;
import java.util.concurrent.ExecutionException;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.FutureTask;
 
public class FiveThreadCount2 {
 private int[] arr={1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28};
 private int total=0;
 public void test() throws InterruptedException, ExecutionException{
  ExecutorService service=Executors.newFixedThreadPool(5);
  int length=arr.length;
  for(int j=0;j<length;j+=(length/5)){
   FutureTask<Integer> task;
   if( (j+(length/5))<length){
    task=new FutureTask<Integer>(new MyCallable(arr, j, j+(length/5)));
   }else{
    task=new FutureTask<Integer>(new MyCallable(arr, j, length));
   }
   service.execute(task);
   total+=task.get();
  }
  service.shutdown();
  System.out.println(total);
 
 }
 
 public class MyCallable implements Callable<Integer>{
  int[] arr;
  int startIndex;
  int endIndex;
  public MyCallable(int[] arr,int startIndex,int endIndex){
   this.arr=arr;
   this.startIndex=startIndex;
   this.endIndex=endIndex;
  }
  @Override
  public Integer call() throws Exception {
   int sum=0;
   for(int i=startIndex;i<endIndex;i++){
    sum+=arr[i];
   }
   System.out.println(Thread.currentThread().getName());
   return sum;
  }
 }
 
}

這個方式有一個缺點(diǎn)，看似5個線程異步執(zhí)行，其實(shí)是順序執(zhí)行，因?yàn)?nbsp;task.get是要等待線程執(zhí)行完畢才會執(zhí)行下邊的代碼。所以效率不會高,可能換種寫法可以解決這個問題，這里就不深入研究。

方式二：

通過java工具類CountDownLatch實(shí)現(xiàn)并發(fā)計算

package test;
 
import java.util.concurrent.CountDownLatch;
 
public class FiveThreadCount3 {
 private int[] arr={1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28};
 private int total=0;
 public void test() throws InterruptedException{
  int length=arr.length;
  CountDownLatch latch=new CountDownLatch(length%5==0?5:6);
  System.out.println(length);
  for(int j=0;j<length;j+=(length/5)){
   MyThread task;
   if( (j+(length/5))<=length){
    task=new MyThread(arr, j, j+(length/5), latch);
   }else{
    task=new MyThread(arr, j, length, latch);
   }
   new Thread(task).start();
  }
  latch.await();
  System.out.println(total);
 }
 
 private class MyThread implements Runnable{
  int[] arr;
  int startIndex;
  int endIndex;
  CountDownLatch latch;
  public MyThread(int[] arr,int startIndex,int endIndex,CountDownLatch latch){
   this.arr=arr;
   this.startIndex=startIndex;
   this.endIndex=endIndex;
   this.latch=latch;
  }
  @Override
  public void run() {
   int sum=0;
   for(int i=startIndex;i<endIndex;i++){
    sum+=arr[i];
   }
   synchronized (MyThread.class) {
    total+=sum;
   }
 
   System.out.println(Thread.currentThread().getName());
   latch.countDown();
 
  }
  
 }
}

對于CountDownLatch不熟悉的可以搜索下用法。

方式三：

通過java工具類 CyclicBarrier實(shí)現(xiàn)并發(fā)計算。

package test;
 
import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CyclicBarrier;
 
 
public class FiveThreadCount1 {
 private int[] arr={1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28};
 private int total=0;
 public void test() throws InterruptedException, BrokenBarrierException{
  int length=arr.length;
  CyclicBarrier barrier=new CyclicBarrier((length%5==0?5:6)+1);
  System.out.println(length);
  for(int j=0;j<length;j+=(length/5)){
   MyThread task;
   if( (j+(length/5))<=length){
    task=new MyThread(arr, j, j+(length/5), barrier);
   }else{
    task=new MyThread(arr, j, length, barrier);
   }
   new Thread(task).start();
  }
  barrier.await();
  System.out.println(total);
 }
 
 private class MyThread implements Runnable{
  int[] arr;
  int startIndex;
  int endIndex;
  CyclicBarrier barrier;
  public MyThread(int[] arr,int startIndex,int endIndex,CyclicBarrier barrier){
   this.arr=arr;
   this.startIndex=startIndex;
   this.endIndex=endIndex;
   this.barrier=barrier;
  }
  @Override
  public void run() {
   int sum=0;
   for(int i=startIndex;i<endIndex;i++){
    sum+=arr[i];
   }
   synchronized (MyThread.class) {
    total+=sum;
   }
   
   try {
    System.out.println(Thread.currentThread().getName());
    barrier.await();
   } catch (InterruptedException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
   } catch (BrokenBarrierException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
   }
  }
  
 }
}