Consider the following scenario:

public class Test
{
    public void foo()
    {
        A a = new A();
        B b = new B();
        
        Base c = a & b; // << "Operator '&' cannot be applied to 'A', 'B'"
        c = a.and(b);
        c = a + b; // << "Operator '+' cannot be applied to 'A', 'B'"
        c = a.add(b);
    }
}

class A implements Base { }

class B implements Base { }

interface Base
{
    default Base and(Base other) { return this;  }
    default Base add(Base other) { return this; }
}

As you might imagine, the functional syntax works fine as "a" implements Base so it has the and/add methods and "b" implements Base so it is a valid parameter.
But the operator syntax cannot recognize them as valid operators.

If I change the parameters from Base to B, it works fine.
Or if I change the variable "B b" to "Base b", it also works fine.
The same also happens if Base is a class.

However, I have 16 classes that all have to be able to use the "and" operator on each other.
And that would result in 16*15 methods with all duplicate code that could very well be in one interface.

I am using IntelliJ Ultimate version 2017.2 with the Java-oo plugin 0.6.
(Javac compiler)