• Status: Solved
  • Priority: Medium
  • Security: Public
  • Views: 232
  • Last Modified:

Identify the type

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;

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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) {
		java.util.Iterator<Class<?>> iterator = paramTypeList.iterator();
		Class<?>[] paramTypeArray = new Class<?>[paramTypeList.size()];
		int count = 0;
		while(iterator.hasNext()) {
			paramTypeArray[count] = iterator.next();
		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;

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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.

Vijay Bhore
1 Solution
CPColinSenior Java ArchitectCommented:
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.
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