Java Eclipse Lambda function error

Question

The following code produces an error for me in Eclipse Luna and prevents from running.

    jdbcTemplate.query( query, r -> {
        Folder folder = new Folder();
        folder.setId(r.getLong("id"));
        folder.setFolderName(r.getString("folder_name"));
        folder.setFullPath(r.getString("full_path"));
        folders.add(folder);
    }, folderId);

    return folders;
}

The error occurs at jdbcTemplate.query

The method query(String, ResultSetExtractor<Object>, Object[]) is ambiguous for the type JdbcTemplate

Error does not occur when I package file as jar and run.

Thanks for any guidance or suggestions.

your lambda expression needs to return an object at the end of it's body — Jack Ammo
– Jack Ammo, Commented May 1, 2016 at 22:36

ctg · Accepted Answer · 2016-05-01 23:05:18Z

3

There are three query methods in JdbcTemplate, as follows:

query(String, ResultSetExtractor<T>);
query(String, RowCallbackHandler);
query(String, RowMapper<T>);

In all three, the second argument can be implemented as a lambda, and the two that have a generic <T> parameter will return something. Eclipse is complaining that it can't tell the difference between the first and the third method you are referring to, so you need to specify the type of the functional interface that the lambda is replacing. Additionally, as Jack Ammo says, you need to return an object from the lambda to satisfy the interface. Don't add the returned object to your list of folders inside the lambda, either. So, you'd be looking at something like this:

Folder folder = jdbcTemplate.query( query, (ResultSetExtractor<Folder>) r -> {
    Folder folder = new Folder();
    folder.setId(r.getLong("id"));
    folder.setFolderName(r.getString("folder_name"));
    folder.setFullPath(r.getString("full_path"));
    return folder;
}, folderId);

folders.add(folder);

return folders;

answered May 1, 2016 at 23:05

ctg

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1 Comment

user2880771 Over a year ago

Thanks! Casting as RowCallbackHandler solved problem.

Jack Ammo · Accepted Answer · 2016-05-01 22:48:09Z

2

according to the javadoc for ResultSetExtractor, the method you're implementing with your lambda expression is Object extractData(ResultSet rs). extractData returns an Object so your lambda also has to return an Object in order to properly implement it.

answered May 1, 2016 at 22:48

Jack Ammo

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