java - 当我通过另一个线程保存她时，为什么我无法显示我的 arrayList？

Question

您好，我在从外部类显示列表时遇到问题。我尝试使用 public void show() 方法，但列表为空。我认为问题出在线程上，这可能吗？谁能解释为什么会发生这种情况？

public class CollectionsOperation
{
    private List<Client> bufferedReaderClientLIst =
        Collections.synchronizedList(new ArrayList<Client>());

    BufferedReader bf = null;

    private static final String fileName = "clients.txt";

    public void bufferedReaderCollection()
        throws IOException
    {
        String line;
        try {
            bf = new BufferedReader(new InputStreamReader(
                new FileInputStream(fileName), "UTF-8"));

            while ((line = bf.readLine()) != null) {
                String[] split = line.split(";"); 
                String nameCompany = split[0].substring(2);
                String adress = split[1]; 
                String phoneNumber = split[2]; 
                String emailAdress = split[3];

                Client k = new Client(nameCompany, adress, phoneNumber, emailAdress);
                bufferedReaderClientLIst.add(k); 
            }
        } catch (IOException e) {
        }
    }

    public void runBufferedReader()
    {
        Thread t = new Thread(new CreateList());
        t.start();
    }

    public void show()
    {
        System.out.println(bufferedReaderClientLIst);
    }

    private class CreateList implements Runnable
    {
        @Override
        public void run()
        {
            CollectionsOperation o = new CollectionsOperation();
            try {
                o.bufferedReaderCollection();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

Answer 1

问题很简单，您的方法 CreateList::run 创建了 CollectionsOperation 的新实例。因此，原始对象方法 show 将不会访问与 CreateList 类填充的列表相同的数据。

相反，您可能想使用

        public void run()
        {
            CollectionsOperation.this.bufferedReaderCollection();
        }

另一种方法是在 CreateList 中创建一个构造函数，并使用 CollectionsOperation 对象作为参数。

public class CollectionsOperation
{
    ...
    public void runBufferedReader()
    {
        Thread t = new Thread(new CreateList(this));
        t.start();
    }
    ...
    private class CreateList implements Runnable
    {
        CollectionsOperation co;
        public CreateList(CollectionsOperation co) {
            this.co = co;
        }

        @Override
        public void run()
        {
            try {
                co.bufferedReaderCollection();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

但是您还应该考虑线程同步以实现对列表的并发访问。