How to Get class of Elements that List Contains?

Question

I have a list like that:

private List myList = new ArrayList();

I want to get the .class of T. How can I do that?

Answer 1

Why do you need to know this? Perhaps this will do what you need

// must be at least one element (and all elements are the same)
Class elementType = myList.get(0).getClass(); 

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The only way to do this is to either

• store the type in a field and add a getter method for this.

like

private final Class type;
private final List list = new ArrayList();

public Class getType() { return type; }

• use getGenericType() on the actual field, assuming the parameter type is NOT generic.
• use a sub class with a specific type.

like

List list = new ArrayList() { }; // create a specific sub-class
final Class listClass = list.getClass();
final ParameterizedType genericSuperclass = (ParameterizedType) listClass.getGenericSuperclass();
Class elementType = (Class) genericSuperclass.getActualTypeArguments()[0];

This has the dis-advantage that you could end up creating lots of anonymous classes and potential confusion with things like ArrayList.class != list.getClass() however list instanceof ArrayList