Question

I am trying to convert the following c# code into java

abstract class BaseProcessor<T> where T : new()
{
 public T Process(HtmlDocument html)
 {
         T data = new T();

        Type type = data.GetType();
        BindingFlags flags = BindingFlags.Public | BindingFlags.Instance | BindingFlags.SetProperty;
        PropertyInfo[] properties = type.GetProperties(flags);
        foreach (PropertyInfo property in properties)
        {
             string value = "test";
             type.InvokeMember(property.Name, flags, Type.DefaultBinder, data, new object[] { value });
        }
 }
}

So i have done upto

public class BaseProcessor<T> 
{
   public T Process(String m_doc)
   {
      T data = (T) new BaseProcessor<T>(); // this is not working

      Document doc = Jsoup.parse(m_doc);
      return data;
   }
}

When i instantiate the data object its not acquiring the properties of the Generic class at runtime
let say for example when i hit the code its not getting properties of DecodeModel class

IDocProcessor<DecodeModel> p = new DecodeThisProcessor();
return p.Process(doc);


public interface IDocProcessor<T>
{
    T Process(String webresponse);
}

public class DecodeThisProcessor extends BaseProcessor<DecodeModel> implements IDocProcessor<DecodeModel>
{
public void setup();
}

So please help me what will be the right syntax to instantiate generic object data

Answer 1

You cannot instantiate generics. The reason is that the type is not available at run-time, but actually replaced with Object by the compiler. So

T data = new T(); // Not valid in Java for a generics T!

would in fact be:

Object data = new Object(); // Obviously not the desired result

Read the Java Generics Tutorial wrt. to “type erasure” for details.

---

You will need to employ the factory pattern.

T data = factory.make();

where

public interface Factory<T> {
     T make();
}

needs to be implemented and passed to the constructor. To make this work, you need a factory that knows how to instantiate the desired class!

A (rather obvious) variant is to put the factory method into your – abstract – class.

public abstract class BaseProcessor<T> 
{
   protected abstract T makeProcessor();

   public T Process(String m_doc)
   {
       T data = makeProcessor(); // this is now working!

and when extending BaseProcessor implement it for the actual final type.