Type System

Analogy: concept

Type Casting is like Disguises:

Upcasting: A Doctor puts on a generic "Human" mask. They are still a Doctor, but you only treat them as a Human. (Safe).
Downcasting: You ask the "Human" to take off the mask. If they really ARE a Doctor, great! If they are actually a Firefighter, you have a problem. (Unsafe).

The Transformer

See how objects can be viewed as their Parent type (Upcasting) or cast back to their specific type (Downcasting).

Type Casting (Transformer)

Original Object

Type: Circle

Object created as a Circle.

Key Concepts

Upcasting: Treating a Child object as a Parent object.
- Always safe.
- Shape s = new Circle();
Downcasting: Treating a Parent reference as a Child object.
- Risky! Requires a check.
- Circle c = (Circle) s;
Type Checking: Using instanceof (Java) or typeof to verify the object before casting.

The Code

class Shape {}
class Circle extends Shape { void roll() {} }
class Square extends Shape { void slide() {} }

// Upcasting (Safe)
Shape s = new Circle(); 

// Downcasting (Risky)
if (s instanceof Circle) {
    Circle c = (Circle) s; // Safe now!
    c.roll();
} else {
    System.out.println("Not a Circle!");
}

// Bad Downcast
Square sq = (Square) s; // Error! ClassCastException.