Why cast after an instanceOf?

Question

In the example below (from my coursepack), we want to give to the Square instance c1 the reference of some other object p1, but only i

Answer 1

The compiler does not infer that since you are in the block, you have done a successful check for the type of the object. An explicit cast is still required to tell the compiler that you wish to reference the object as a different type.

if (p1 instanceof Square) {
    // if we are in here, we (programmer) know it's an instance of Square
    // Here, we explicitly tell the compiler that p1 is a Square
    c1 = (Square) p1;
}

In C# you can do the check and the cast in 1 call:

c1 = p1 as Square;

This will cast p1 to a Square, and if the cast fails, c1 will be set to null.