Why return type of same-named-method should be same in sub-class Java?

Question

My background is C++. I know what is overloading and what is the overriding. I want to ask if I don\'t want to override the method from the parent and want to make my own me

Answer 1

Because all methods in Java are "virtual" (i.e. they exhibit subtype polymorphism). C++ also disallows conflicting return types when overriding virtual member functions.

struct Base {
    virtual void f() {}
};

struct Derived : Base {
    int f() override { return 0; }
};

Compiler output:

8 : error: conflicting return type specified for 'virtual int Derived::f()'
int f() { return 0; }
^
3 : error: overriding 'virtual void Base::f()'
virtual void f() {}
^

Note that only conflicting return types are disallowed. Different return types are allowed, as long as they are compatible. For example, in C++:

struct Base {
    virtual Base* f() { return nullptr; }
};

struct Derived : Base {
    Derived* f() override { return nullptr; }
};

And in Java:

class Base {
    Base f() { return null; }
}

class Derived extends Base {
    @Override
    Derived f() { return null; }
}