Same source code, Eclipse build success but Maven (javac) fails

Question

Keep getting this error when compiling using Maven:

type parameters of X cannot be determined; no unique maximal instance exists for type variable X wit         


        

Answer 1

A few things to look at:

1. Both Eclipse and Maven are using the same java/bin installation
2. Eclipse and Maven are using the same libraries, one might have something the other does not.

Answer 2

I met the same error,use ant. Because when compile by ant or maven,javac use JDK to compile.But in eclipse,it has JDT,that can compile success.

I add below script in my build.xml file: <property name="build.compiler" value="org.eclipse.jdt.core.JDTCompilerAdapter" /> Then,ant can build success.

I am not familiar with Maven. Maybe,it can set the compiler?

In my source code,there are many code like this: public <X> X find(String hql, Object... values) { return (X) HibernateUtils.createQuery(getSession(), hql, values).uniqueResult(); }

Maybe your code too.

But,use JDT,the success is't the final success,in ant. build.xml can build success only in eclipse. when I run ant from windows command,fail. Throw another error: Class not found: org.eclipse.jdt.core.JDTCompilerAdapter

PS, I have copy jar files about JDT in eclipse plugin to ant_home/lib directory.

Wish a little help to you.And our problem can solve.

Answer 3

It definitely has to do something with the JDK versions maven and eclipse are using. Also make sure your Compiler compliance level in eclipse points to the right JDK version.

Answer 4

This issue can occur when your code is generic and it calls another method that has a generic return type. Sometimes the compiler gets confused trying to figure out how to resolve the method call / return type.

It can be resolved by adding an explicit cast to your code.

// Old code:
public T getValue() {
    return otherMethod();  // otherMethod has the signature: <RT> RT otherMethod() { ... }
}

// New code:
@SuppressWarnings("unchecked")
public T getValue() {
    return (T) otherMethod();   // the cast tells the compiler what to do.
}