I have;
JavaScript
x
List<String> stringList = new ArrayList<String>();
List<Integer> integerList = new ArrayList<Integer>();
Is there a (easy) way to retrieve the generic type of the list?
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Answer
If those are actually fields of a certain class, then you can get them with a little help of reflection:
JavaScript
package test;
import java.lang.reflect.Field;
import java.lang.reflect.ParameterizedType;
import java.util.ArrayList;
import java.util.List;
public class Test {
List<String> stringList = new ArrayList<String>();
List<Integer> integerList = new ArrayList<Integer>();
public static void main(String args) throws Exception {
Field stringListField = Test.class.getDeclaredField("stringList");
ParameterizedType stringListType = (ParameterizedType) stringListField.getGenericType();
Class<?> stringListClass = (Class<?>) stringListType.getActualTypeArguments()[0];
System.out.println(stringListClass); // class java.lang.String.
Field integerListField = Test.class.getDeclaredField("integerList");
ParameterizedType integerListType = (ParameterizedType) integerListField.getGenericType();
Class<?> integerListClass = (Class<?>) integerListType.getActualTypeArguments()[0];
System.out.println(integerListClass); // class java.lang.Integer.
}
}
You can also do that for parameter types and return type of methods.
But if they’re inside the same scope of the class/method where you need to know about them, then there’s no point of knowing them, because you already have declared them yourself.