incompatible types (generics)

Question

I'm getting

incompatible types; inferred type argument(s) java.lang.Object do not conform to bounds of type variable(s) T
[ERROR] found   : <T>int
[ERROR] required: int
[ERROR] -> [Help 1]

for my method

private <T extends Comparable<T>> int useComparator(final Object o1, final Object o2, final String property) {
    final T s1 = new PropertyModel<T>(o1, property).getObject();
    final T s2 = new PropertyModel<T>(o2, property).getObject();
    return s1.compareTo(s2);
}

where PropertyModel is org.apache.wicket.model.PropertyModel, but in fact this is not important much (this class simply returns value of some field, btw: is there some class with similar function in Spring for example?).

Problem is at line calling that method:

return this.useComparator(o1, o2, sortProperty);

I can fix this by

return this.<Comparable> useComparator(o1, o2, sortProperty);

but I'm wondering..I have no problem when compiling such code in Eclipse and NetBeans. As far as I can see I'm using same java, but in Maven I'm getting the error from the beggining of the post. Is there some compiler flag that I missed?

Not sure if that helps, but my Maven version is:

> mvn -version
Apache Maven 3.0.4 (r1232337; 2012-01-17 09:44:56+0100)
Maven home: c:\Programs\apache-maven-3.0.4
Java version: 1.6.0_37, vendor: Sun Microsystems Inc.
Java home: c:\Java\jdk1.6.0_37\jre
Default locale: sk_SK, platform encoding: Cp1250
OS name: "windows 7", version: "6.1", arch: "amd64", family: "windows"

Maven compiler plugin setting from pom.xml:

<plugin>
    <groupId>org.apache.maven.plugins</groupId>
    <version>2.5.1</version>
    <inherited>true</inherited>
    <artifactId>maven-compiler-plugin</artifactId>
    <configuration>
        <source>1.6</source>
        <target>1.6</target>
        <encoding>UTF-8</encoding>
    </configuration>
</plugin>

edit: requested code added

Create the wicket project (just for dependencies). I used Wicket Quickstart page to generate maven project. I used:

mvn archetype:generate -DarchetypeGroupId=org.apache.wicket -DarchetypeArtifactId=wicket-archetype-quickstart -DarchetypeVersion=6.6.0 -DgroupId=net.betlista -DartifactId=stackoverflow -DarchetypeRepository=https://repository.apache.org/ -DinteractiveMode=false

Import the project to your favorite IDE.

Use this JUnit test to simulate the problem:

package net.betlista;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;

import junit.framework.Assert;

import org.apache.wicket.extensions.markup.html.repeater.util.SortParam;
import org.apache.wicket.model.PropertyModel;
import org.junit.Test;

public class ComparatorTest {

    @Test
    public void test() {
        final ArrayList<Person> persons = new ArrayList<Person>();

        final Person alice = new Person("Alice", 30);
        persons.add(alice);
        final Person bob = new Person("Bob", 20);
        persons.add(bob);

        Collections.sort(persons, new PropertyComparator(new SortParam<String>("name", true)));
        Assert.assertEquals(alice, persons.get(0));
        Assert.assertEquals(bob, persons.get(1));

        Collections.sort(persons, new PropertyComparator(new SortParam<String>("name", false)));
        Assert.assertEquals(alice, persons.get(1));
        Assert.assertEquals(bob, persons.get(0));

        Collections.sort(persons, new PropertyComparator(new SortParam<String>("age", true)));
        Assert.assertEquals(alice, persons.get(1));
        Assert.assertEquals(bob, persons.get(0));

        Collections.sort(persons, new PropertyComparator(new SortParam<String>("age", false)));
        Assert.assertEquals(alice, persons.get(0));
        Assert.assertEquals(bob, persons.get(1));
    }

    static class Person {
        String name;
        Integer age;

        public Person(final String name, final Integer age) {
            this.name = name;
            this.age = age;
        }
    }

    private static class PropertyComparator implements Comparator<Object> {

        private SortParam<String> sort;

        public PropertyComparator(final SortParam<String> sort) {
            this.sort = sort;
        }

        @Override
        public int compare(final Object o1, final Object o2) {
            final int dir = sort.isAscending() ? 1 : -1;

            final String sortProperty = sort.getProperty();
            return dir * this.useComparator(o1, o2, sortProperty);
        }

        private <T extends Comparable<T>> int useComparator(final Object o1, final Object o2, final String property) {
            final T p1 = new PropertyModel<T>(o1, property).getObject();
            final T p2 = new PropertyModel<T>(o2, property).getObject();
            return p1.compareTo(p2);
        }

    }

}

In my environment this works fine in Eclipse, but fails when tried to compile using

mvn clean install

When I tried to move useComparator out of PropertyComparator and made it static didn't help...