No instance(s) of type variable(s) T exist so that List<T> conforms to Integer

Question

In the following code:

return new HashSet<>(namedParameterJdbcTemplate.query(
    SOME_SQL_QUERY_STRING,
    parametersMap,
    (resultSet, rowNum) -> resultSet.getBigDecimal("GETID")
));

I'm getting a red line under (resultSet, rowNum) -> resultSet.getBigDecimal("GETID")) and the following error : No instance(s) of type variable(s) T exist so that List<T> conforms to Integer. Can someone please help me and tell why this is happening?

Answer 1

The fundamental problem is that a different (unwanted) overloaded version of the "query" method is inferred (based on the code) and the lambda (Function) given as third parameter is not appropriate for this version of "query".

A way to fix this is to "force" the query function you want by providing the type parameter as such:

return new HashSet<>(namedParameterJdbcTemplate.<BigDecimal>query( ...

Answer 2

add an explicit casting to your method call

in my case I have

<T> Map<String, T> getMap(@NotNull String rootPath, @NotNull Class<T> type)

and I used it like

LinkedHashMap<String,String> x = xmlRegestryFile.getMap("path/to/map/of/string", String.class)

but it failed and gave me that error, so I overcomed this error by adding casting

x = (LinkedHashMap<String, String>) xmlRegestryFile.getMap("my/path", String.class)