如何在类中填充通用容器？
我正在尝试编写一个列表（用于系统类项目），该列表将通过套接字连接进行序列化。
需求规范规定，列表应该通过写入长度的 int，然后写入每个元素来序列化。
此外，应该有一个（非静态）readFrom(InputStream in) 方法从流中读取数据。
我想知道是否有一种方法可以创建一个通用的 WritableList 对象，该对象作为参数，并在调用 readFrom 时填充自身？
据我所知，如果没有一些黑客反射，你无法真正获得对象内部泛型类型的类型。所以我正在考虑将类作为构造函数中的参数传递，就像这样
public class WritableList<E extends Writable> extends ArrayList<E> implements Writable {
Class<E> storedClass;
protected WritableList(Class<E> storedClass)
{
this.storedClass = storedClass;
}
@Override
public void readFrom(InputStream in) throws IOException {
int length = DataTypeIO.readInt(in);
this.clear();
for (int i = 0; i < length; i++)
{
E e;
try {
e = storedClass.newInstance();
e.readFrom(in);
add(e);
} catch (InstantiationException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
} catch (IllegalAccessException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
}
}
}
但是，我现在不完全确定如何将 WritableList 作为类传递。当我尝试像这样实例化它时：
grid = new WritableList<WritableList<Location>>(**What goes here?**);
我不确定要传入什么样的类。我对 java 反射不太有经验，所以这里的任何帮助都会很棒。谢谢
I'm trying to write a List (for a systems class project) that is going to be serialized through a socket connection.
The requirement specs says that a List should be serialized by writing an int for the length, then writing each element.
Also, there should be a (non-static) readFrom(InputStream in) method that reads in the data from a stream.
I was wondering if there is a way to create a generic WritableList object that takes as a parameter, and populates itself when readFrom is called?
From what I know, you can't really get the type of the generic type inside the object without some hacky reflection. So I was thinking of passing the class as a parameter in the constructor like so
public class WritableList<E extends Writable> extends ArrayList<E> implements Writable {
Class<E> storedClass;
protected WritableList(Class<E> storedClass)
{
this.storedClass = storedClass;
}
@Override
public void readFrom(InputStream in) throws IOException {
int length = DataTypeIO.readInt(in);
this.clear();
for (int i = 0; i < length; i++)
{
E e;
try {
e = storedClass.newInstance();
e.readFrom(in);
add(e);
} catch (InstantiationException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
} catch (IllegalAccessException e1) {
// TODO Auto-generated catch block
e1.printStackTrace();
}
}
}
}
However, I'm not entirely sure how to pass in a WritableList as a class now. When I try to instantiate it like so:
grid = new WritableList<WritableList<Location>>(**What goes here?**);
I'm not sure what kind of class to pass in. I'm not too experienced with java reflection, so any help here would be great. Thanks
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我的猜测应该是
new WritableList(Location.class) My guess is it should bew
new WritableList<Location>(Location.class)我认为问题出在这个设计上。需要首先使用
.newInstance()实例化类，然后使用它来调用.readFrom()，这是没有意义的。.newInstance()在代码中使用时通常是一个坏兆头，因为它假设存在无参构造函数（在本例中，您的WritableList不存在该构造函数）类），即使它存在，它也会强制您使用无参构造函数，从而阻止将数据传递到对象中。I think the problem is with the design of this. It doesn't make sense to need to first instantiate the class using
.newInstance()and then use that to call.readFrom()..newInstance()is generally a bad sign when used in code, because it assumes the existence of a no-argument constructor (which does not exist in this case for yourWritableListclass), and even if it exists, it forces you to use the no-argument constructor, preventing one from passing data into the object.