Want to win a PS4? Go Premium and enter to win our High-Tech Treats giveaway. Enter to Win

x
?
Solved

Identify the type

Posted on 2012-04-12
1
Medium Priority
?
229 Views
Last Modified: 2012-08-13
I have written a method as follows,

public static <T> List<T> add(List<T> list, T t) {
    if(list == null) return null;
    if(t == null) return list;

    List<T> outputList = new ArrayList<T>(list);
    outputList.add(t); // append item into list

    return outputList;
}

Open in new window


I want to understand the Class for it's input parameters. I am using the following code for this purpose,

   
private static Class<?>[] getParameterTypes(Method method) {
		Type[] t = method.getGenericParameterTypes();
		List<Class<?>> paramTypeList = new ArrayList<Class<?>>();
		
		for(Type arg: t) {
			paramTypeList.add(getClass(arg));
		}
				
		java.util.Iterator<Class<?>> iterator = paramTypeList.iterator();
		Class<?>[] paramTypeArray = new Class<?>[paramTypeList.size()];
		int count = 0;
		
		while(iterator.hasNext()) {
			paramTypeArray[count] = iterator.next();
			count++;
		}
		
		return paramTypeArray;
	}
        
private static <T> Class<?> getClass(Type type) {
		if (type instanceof Class<?>) {
			return (Class<?>) type;
		} else if (type instanceof ParameterizedType) {
			return getClass(((ParameterizedType) type).getRawType());
		} else if (type instanceof GenericArrayType) {
			Type componentType = ((GenericArrayType) type).getGenericComponentType();
			Class<?> componentClass = getClass(componentType);
			if (componentClass != null) {
				return Array.newInstance(componentClass, 0).getClass();
			} else {
				return null;
			}
		} else {
			return null;
		}
	}

Open in new window


The problem is that for the argument T, the getClass method returns null and my business logic fails. Can anybody suggest a way to identify the class of T.

Thanks,
Vijay Bhore
0
Comment
Question by:vijaybhorems
[X]
Welcome to Experts Exchange

Add your voice to the tech community where 5M+ people just like you are talking about what matters.

  • Help others & share knowledge
  • Earn cash & points
  • Learn & ask questions
1 Comment
 
LVL 14

Accepted Solution

by:
CPColin earned 1000 total points
ID: 37840405
You probably can't get the type from the List, because generic types are erased at runtime (search for a phrase like "java type erasure" for more details). However, since you're passing an object of type T to that add() method, you could just call getClass() on that object.
0

Featured Post

Free Tool: Port Scanner

Check which ports are open to the outside world. Helps make sure that your firewall rules are working as intended.

One of a set of tools we are providing to everyone as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

By the end of 1980s, object oriented programming using languages like C++, Simula69 and ObjectPascal gained momentum. It looked like programmers finally found the perfect language. C++ successfully combined the object oriented principles of Simula w…
In this post we will learn different types of Android Layout and some basics of an Android App.
Viewers will learn about the different types of variables in Java and how to declare them. Decide the type of variable desired: Put the keyword corresponding to the type of variable in front of the variable name: Use the equal sign to assign a v…
Viewers will learn about the regular for loop in Java and how to use it. Definition: Break the for loop down into 3 parts: Syntax when using for loops: Example using a for loop:
Suggested Courses

610 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question