Skip to main content

Maven Only: type parameters of X cannot be determined

This is a rare error that compiling with Eclipse does not catch, but maven compile goal will. In the case in question, There is a Generic return type as follows, as discussed in java forums

private <A> A getValue(){
    return getOtherValue(); //<--  Error occurs here

It compiles out an error:

type parameters of <X>X cannot be determined; no unique maximal instance exists for type variable X with upper bounds int,java.lang.Object

The intriguing question is, why does this happen only in maven? Why does it not happen in Eclipse? Few in the java forum have suggested that this is a bug in the compiler. However, an impatient programmer looking for a solution around it, Just cant get it. There is an unanswered stack overflow post here. The java forum is also confusing for a novice.

The simple answer here is, the getValue() method (or the getOtherValue, or the method it calls) is, at some place, not really Strongly typed and the compiler is left to guess wildly about what type the return value actually is. To overcome it, the whole call chain need to infer generics or simply perform an unchecked type cast. The solution will be strongly typed after the call in the chain.

private <A> A getValue(){
    return (A) getOtherValue(); //<--  No Error now

Popular posts from this blog

Javascript: Convert Strings to Binary (and representing in a nerdy way!)

I follow those GoogleDevelopers Videos. Sometime back, in one of the presentations on GoogleIO, there was this interesting string of dots at the bottom of each page of the presentation. They looked like random big and small dots. A similar bunch of dots were also on the T-shirt of a presenter was wearing in another presentation. While it seemed something in the pattern, I could not find what it was. Finally, another presenter cleared the matter that those dots are just binary representation of "GOOGLEIO" (So much for advertizing Google IO, Impressive!).

So I wanna do it. Takes me back to days of those DSP classes at school. Nerdy me had to churn some old brain cells. I remember those first programming language classes in Pascal and C when you were asked to do fibonacci series and converting a binary string to ascii codes. That *experience* came handy here: Check it out!

Text to Binarize:
For those who came to copy the javascript code to convert string to binary, Here it is…

Add jquery in Chrome console

Many a time, a page you are debugging doesnot have jquery. This simple js will add(or prompt you to overwrite) jquery to any page from chrome console.


MySql Copying Table Structures.

Some times you need to copy only table structures across databases. This article describes two ways of doing it.

If the whole database schema need to be exported, mysqldump is very effective. A --nodata flag will dump all tables' schema.

Like this.
mysqldump --nodata -p -u username databaseName
But if you want to copy a specific table, individually, you could use "create table like" feature. You could create it even from a different database. However it must be on the same mysqld instance.

Like this.
create table newtable like oldtable; --Or from a table in other database create table mytable like otherdatabase.tablename;