Java 不存在类型变量 T 的实例，因此 List<T> 符合 Integer
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No instance(s) of type variable(s) T exist so that List<T> conforms to Integer
提问by cnova
In the following code:
在以下代码中：
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?
我(resultSet, rowNum) -> resultSet.getBigDecimal("GETID"))在下面看到一条红线，并出现以下错误：No instance(s) of type variable(s) T exist so that List<T> conforms to Integer。有人可以帮助我并告诉我为什么会这样吗？
采纳答案by Ovidiu Dolha
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".
根本问题是推断出“查询”方法的不同（不需要的）重载版本（基于代码），并且作为第三个参数给出的 lambda（函数）不适用于此版本的“查询”。
A way to fix this is to "force" the query function you want by providing the type parameter as such:
解决此问题的一种方法是通过提供类型参数来“强制”您想要的查询功能：
return new HashSet<>(namedParameterJdbcTemplate.<BigDecimal>query( ...
回答by Basheer AL-MOMANI
add an explicit casting to your method call
向您的方法调用添加显式转换
in my case I have
就我而言，我有
<T> Map<String, T> getMap(@NotNull String rootPath, @NotNull Class<T> type)
and I used it like
我用它就像
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
但它失败了并给了我那个错误，所以我通过添加强制转换来克服这个错误
x = (LinkedHashMap<String, String>) xmlRegestryFile.getMap("my/path", String.class)
