Get type of generic type inside a List in Java

Question

I have the below function:

    public  void putList(String key, List lst){
          if (T instanceof String) {
          // Do something              


        

Answer 1

It's not possible in Java due to erasure. What most people do instead is add a type token. Example:

public  void putList(String key, List list, Class listElementType) {
}

There are certain situations where reflection can get at the type parameter, but it's for cases where you've pre-set the type parameter. For example:

public class MyList extends List {
    private List myField;
}

In both of those cases reflection can determine the List is of type String, but reflection can't determine it for your case. You'd have to use a different approach like a type token.