import java.util.List; import java.util.Map; import lombok.experimental.ExtensionMethod; @ExtensionMethod(ExtensionMethodGeneric.Extensions.class) class ExtensionMethodGeneric { public void test() { List<String> stringList = null; List<Number> numberList = null; stringList.test(); stringList.test(numberList); stringList.test(stringList).test(numberList); Integer i = stringList.test2(); Map<String, Integer> map = null; List<String> l = map.test(stringList, numberList); } static class Extensions { public static <T> List<T> test(List<String> obj, List<T> list) { return null; } public static <K,V> K test(Map<String, Integer> obj, K k, V v) { return k; } public static <T> T test(List<T> list) { return null; } public static <T,U> U test2(List<T> list) { return null; } } }