Java generics with unbounded wildcard?

Question

I have an interface to convert object to string:

public interface Converter {
    String asString(T object);
}

And a map to store

Answer 1

You are facing issue called wildcard capture. Java is unable to identify the type that will be received from the List data. Try refactoring your code in any of the two ways

Method 1: Change your interface as below

interface Converter {
    String asString(Object object);
}

Method 2: Helper method to capture wild card by type inference

Create an helper method as below,

// Helper method created so that the wildcard can be captured
// through type inference.
private  void helper(List data) {
    Map, Converter> converterMap = null;
    List stringData = null;

    for (T datum : data) {
        stringData.add(converterMap.get(datum.getClass()).asString(datum));
    }
}

Call this helper method as below

List data = fetchData();
helper(data);