java - 如何让线程仅添加到一个带有同步整数的数组列表

Question

我一直在尝试做一些简单的事情，比如将两个线程添加到一个数组列表中，但出于某种原因我无法让它工作。我有同步方法并使用 Collections.synchronized 列表，但它仍然显示它正在打印两个单独的数组。我编写了一个简短的程序，以便更好地理解运行两个线程来访问一个 arrayList。如果有人能够阐明我犯了什么错误，我们将不胜感激!

这是主类

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class RunThreads {
    public static void main(String[] args) {
        ExecutorService executor = Executors.newCachedThreadPool();
        int[] numbers1 = {0, 2, 4, 6, 8};
        int[] numbers2 = {1, 3, 5, 7, 9};
        executor.execute(new ThreadToRun(numbers1));
        executor.execute(new ThreadToRun(numbers2));
        executor.shutdown();
    }
}

这是 TheadToRun 类:

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class ThreadToRun implements Runnable {
    List<Integer> list = Collections.synchronizedList(new ArrayList<Integer>());
    private int[] array;

    public ThreadToRun(int[] array) {
        this.array = array;
    }

    public void run() {
        list = adder(array);
        for(int i=0; i<list.size(); i++){
            System.out.print(list.get(i)+"("+i+")"); //print out the element at i and the index 
        }                                            //to see if there are two arrays with the same index
    }

    public  List<Integer> adder(int [] a){
        List<Integer> list = Collections.synchronizedList(new ArrayList<Integer>());
        for (int array : a) {
            synchronized(list){
                list.add(array);
            }
        }
        return list;
    }
}

Answer 1

在这里，您将创建两个“TheadToRun”实例，每个实例实例化一个新的列表实例(如下所述)

List<Integer> list = Collections.synchronizedList(new ArrayList<Integer>());

此外，在您的加法器方法中，您还执行以下操作:

List<Integer> list = Collections.synchronizedList(new ArrayList<Integer>());

这将再次创建一个新列表并覆盖实例中的现有列表。

可能的解决方案:

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class ThreadToRun implements Runnable {
    List<Integer> list;
    private int[] array;

    public ThreadToRun(int[] array, List<Integer> list) {
        this.array = array;
        this.list = list;
    }

    public void run() {
        for (int array : a) {
            list.add(array);
        }
    }
}


import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class RunThreads {
    public static void main(String[] args) {
        ExecutorService executor = Executors.newCachedThreadPool();
        int[] numbers1 = {0, 2, 4, 6, 8};
        int[] numbers2 = {1, 3, 5, 7, 9};

        List<Integer> list = Collections.synchronizedList(new ArrayList<Integer>());

        ThreadToRun t1 = new ThreadToRun(numbers1, list);
        ThreadToRun t2 = new ThreadToRun(numbers1, list);

        executor.execute(t1);
        executor.execute(t2);
        executor.shutdown();

        // print the list out
        for(int i=0; i<list.size(); i++){
            System.out.print(list.get(i) + " found at location ("+i+")");
        }
    }
}