Java - Error : return type is incompatible

Question

I'm learning java. I was trying to run the code, where I got this error: return type is incompatible. Part of code where it showed me error.

class A {
    public void eat() { }
}

class B extends A {
    public boolean eat() { }
}

Why it is happening?

Answer 1

This is because we cannot have two methods in classes that has the same name but different return types.

The sub class cannot declare a method with the same name of an already existing method in the super class with a different return type.

However, the subclass can declare a method with the same signature as in super class. We call this "Overriding".

You need to have this,

class A {
    public void eat() { }
}

class B extends A {
    public void eat() { }
}

OR

class A {
    public boolean eat() { 
        // return something...
    }
}

class B extends A {
    public boolean eat() { 
        // return something...
    }
}

A good practice is marking overwritten methods by annotation @Override:

class A {
    public void eat() { }
}

class B extends A {
    @Override
    public void eat() { }
}

Answer 2

if B extends A then you can override methods (like eat), but you can't change their signatures. So, your B class must be

 class B extends A {
        public void eat() { }
 }

Answer 3

B extends A should be interpreted as B is a A.

If A's method doesn't return anything, B should do the same.