类型安全：未选中从Object转换到ArrayList的＆LT;＆MyVariable的GT; [英] Type safety: Unchecked cast from Object to ArrayList<MyVariable>

问题描述

下面是发送一个ArrayList从服务器到客户端的程序的一部分。我想删除有关此code中的最后一行警告：

Here is a part of a program that sends an ArrayList from a server to a client. I want to remove the warning about the last line in this code:

客户端code：

Socket s;
(...)
// A server is sending a list from the other side of the link.
ois = new ObjectInputStream(s.getInputStream());
MyList = (ArrayList<MyVariable>) ois.readObject();

MyVariable的是具有某些属性的Java类。服务器创建一个ArrayList和MyVariable的变量项目填充它。然后它发送完整列表到客户端。

MyVariable is a Java class with some attributes. The server is creating an ArrayList and filling it with MyVariable variables as items. Then it sends the complete list to the client.

我想知道为什么我有一个警告那里，如何完美地code才能有0个警告。如果有可能，我想避免使用@燮pressWarnings（未登记）。 ;）

I would like to know why do I have a warning there and how to code perfectly in order to have 0 warnings. If it is possible I would like to avoid using "@SuppressWarnings("unchecked")". ;)

感谢您，

路易斯

推荐答案

试试这个

Object obj = ois.readObject();
// Check it's an ArrayList
if (obj instanceof ArrayList<?>) {
  // Get the List.
  ArrayList<?> al = (ArrayList<?>) obj;
  if (al.size() > 0) {
    // Iterate.
    for (int i = 0; i < al.size(); i++) {
      // Still not enough for a type.
      Object o = al.get(i);
      if (o instanceof MyVariable) {
        // Here we go!
        MyVariable v = (MyVariable) o;
        // use v.
      }
    }
  }
}

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