Type Casting Summary

Run-Time Class Mismatch

• Occurs when actual type doesn't match expected type
• Can lead to runtime errors
• Example:

  GetAreable[] shapes = new GetAreable[] {
    new Circle(p, 2),
    new Square(p, 5)
  };
  Circle c = (Circle) shapes[1];  // Runtime error: Square cannot be cast to Circle
  

Type Casting Basics

• Converting between compatible types
• Must be explicitly done for narrowing conversions
• Syntax: (Type) expression
• Example:

  Shape s = new Circle(p, 1.0);
  Circle c = (Circle) s;  // explicit cast needed
  

Safe Casting Practices

• Always check type before casting
• Use instanceof operator
• Example:

  if (shape instanceof Circle) {
    Circle c = (Circle) shape;  // safe cast
    // use c
  }
  

Common Casting Scenarios

1. Upcasting (Widening):

   Circle c = new Circle(p, 1.0);
   Shape s = c;  // no cast needed
   

2. Downcasting (Narrowing):

   Shape s = getShape();
   Circle c = (Circle) s;  // cast needed
   

Casting with Generics

• Cannot create generic array
• Type erasure affects casting
• Example:

  // Not allowed:
  T[] array = new T[10];  // compile error
  
  // Correct way:
  T[] array = (T[]) new Object[10];
  

Best Practices

• Minimize use of casting
• Always validate types before casting
• Use generics when possible
• Document casting requirements
• Handle potential ClassCastException
• Design to avoid need for casting