How does one use polymorphism instead of instanceof? (And why?)

Question

If we take the code below:

Shape p1 = new Square();
Square c1;
if(p1 instanceof Square) {
  c1 = (Square) p1;
}

What does it mean t

Answer 1

Polymorphism lets you change the behaviour of something depending on which type is it. Not sure how to explain it with your example since you could just assign it to a Square straight away if it is important that it is a Square for some reason. Sometimes you need to subclass as it might have additional behaviour etc, but consider this example:

class Shape
{
    abstract void draw();
}

class Square extends Shape
{
    void draw()
    {
        // square drawing goes here
    }
}

The draw method here is an example of polymorphism as we have a base class Shape that says that all shapes now how to draw themselves, but only the Square knows how to draw a Square.