使用通用参数实例化通用类时出错

Question

I have created a generic JAXB serializing class which looks like this:

public class JAXBSerializing<T>
    implements IXMLSerializing<T>
{
private final Class<T> mType;

public JAXBSerializing(Class<T> oType)
{
    mType = oType;
}

}

Now in my code when I instantiate it with a "normal" class, it works fine.

IXMLSerializing<String>strser = new JAXBSerializing<String>(String.class);

But when I try to use a generic class I get a compiler error:

MapEntry<String, String>e = new MapEntry<String, String>("Key", "Value");
IXMLSerializing<MapEntry<String, String>>serializer = new JAXBSerializing<MapEntry<String, String>>(MapEntry.class);

I tried various combinations but none of them work.

IXMLSerializing<MapEntry<String, String>>serializer = new JAXBSerializing<MapEntry<String, String>>(MapEntry<String, String>.class);

Syntax error on token ">", void expected after this token

or

IXMLSerializing<MapEntry<String, String>>serializer = new JAXBSerializing<MapEntry<String, String>>(MapEntry.class);
The constructor JAXBSerializing<MapEntry<String,String>>(Class<MapEntry>) is undefined

The only thing that works is when I instantiate a dummy object like this:

MapEntry<String, String>e = new MapEntry<String, String>("Key", "Value");
IXMLSerializing<MapEntry<String, String>>serializer = new JAXBSerializing<MapEntry<String, String>>((Class<MapEntry<String, String>>) e.getClass());

While this works, I wonder how to properly pass the class as a parameter without that dummy object. And even so, I get an unchecked type warning because of the unneccessary cast, though the objects are all of the correct type.

Answer 1

You can strip the type parameter on the constructor and surpress the warning

public JAXBSerializing(Class<?> oType)
{
    mType = oType;
}

Then this should not yield compiler error

IXMLSerializing<MapEntry<String, String>> serializer = new JAXBSerializing<MapEntry<String, String>>(MapEntry.class);