如何在 Java 中使用多线程和 ArrayList [英] how to use Multithreading With ArrayList in Java

问题描述

你好，

我有一个完美运行的程序，不幸的是我有一些计算需要很多时间，几分钟..

I have a program that works perfectly , unfortunantly i have some calculs that takes a lot of time , some minutes ..

我的目标是使用多线程来加速需要很多时间的部分.

My objectif is to use multithreading to accelerate the parts that take so much time ,.

在这个例子中，我给出了我应该并行化的部分的原型

In this Example I give the prototype of the part that i should parallelize

public static ArrayList<Object2> createListOfObject2(ArrayList<Object1> mylist) {
    ArrayList<Object2> listToReturn = new ArrayList<>();
    Object2 object2;
    for (int i = 0; i < mylist.size(); i++) {
        for (int j = 0; j < mylist.size(); j++) {
            object2 = heavyCalcul(mylist, i, j);
            listToReturn.add(object2);
        }
    }
    return listToReturn;
}
private static Object2 heavyCalcul(ArrayList<Object1> mylist, int i, int j) {
    int weight = MyCalculator.getInstance().calcul(mylist.get(i),mylist.get(j));
    Object2 Object2 = new Object2(weight);
    return Object2;
}

如你所见，方法

public static ArrayList<Object2> createListOfObject2(ArrayList<Object1> mylist)

获取 Object1 的列表，并且应该创建另一个 object2 的列表.

get a list of Object1 , and should create another list of object2 .

我做了一个 twoo foo 循环，每次我创建一个由两个 object 形成的 object2 时，它应该花费 O(n²) 次.

I made a twoo foor Loop , and each time i create an object2 forming by two object , it should take O(n²) times.

更大的列表需要很长时间.

for bigger list it takes a long time.

那么我应该把多线程和我应该使用的列表类型放在哪里.

So where should I put the multithreding and wich type of list i should use.

第二个问题是 MyCalculator 类是一个单例类，我只创建了它的一个对象，在我看来，即使使用多读，真正的程序也不会从多读中受益.

The second Problem is that the class MyCalculator is a singleton Class , and i create only one object of it , and in my opinion even using multhitreading the real program will not benefit of multhitreading .

我应该遵循什么规则来使用多线程阅读?

What are the rules i should follow to use multhitreading ?

非常感谢.

推荐答案

您的对象是单例这一事实无关紧要.重要的是共享可变状态.因此，如果您的计算不改变共享状态，并且每个计算都因此独立于其他计算，您可以只使用并行流:

The fact that your object is a singleton is irrelevant. What matters is shared mutable state. So, if your computation don't mutate shared state, and every computation is thus independant from the others, you can just use a parallel stream:

myList.parallelStream()
      .flatMap(first -> myList.stream().map(second -> MyCalculator.getInstance().calcul(first, second)))
      .collect(Collectors.toList());

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