polymorphism in java

Yes.. Method overloading is compile time as we are passing different argument.

 public void getEmpName(int empId) {
    ......
}

public void getEmpName(String empName) {
    ......
}

public void getEmpName(int empId, String empName) {
    ......
}

and in method overriding is same signature from parent and subclass. so, if you use interface based programming while execution only it will be decided as runtime.

Now coming to your question, I see stackoverflow discussion but IMO overloading is polymorphism. If you see the implementation of System.out.println method there are 10 implementation. Now as a user just use the method and compare with the definition of polymorphism. If it is fulfilling the criteria then yes, overloading is a polymorphism.

 polymorphism means that some code or operations or objects behave differently in different contexts.

#-Link-Snipped-#.
Some say overloading is ad-hoc but as per definition, if code is behaving differently at different scenario then its polymorphism.