Object Type Conversion

• Similarity with primitive conversion

  Converting from one type to another

• Difference

  Primitive type variables store values. So when we convert from a larger to type to smaller type, we might end up loosing information.

  Reference variables on the other hand do not contain the object itself, but its reference. So when we convert types of objects, we're not changing the object, but we're just changing the label on the object, expanding or narrowing the opportunities to work with.

  Upcasting narrows the list of methods and properties available to this object and down casting can extend it.

Upcasting in Java

Implicit Casting

Downcasting in Java

Syntax

• Explicit Casting

• Same as narrowing conversion in primitive data types

  float a = 10.5;
  int b = (int) a;
  
  print(a) -→ 10.5
  print(b) -→ 10
  
  Animal animal = new Animal();
  Cat cat = (Animal) animal;    
  

• Another way

  Animal animal = new Animal();
  if (Cat.class.isInstance(animal)) {
  Cat cat = Cat.class.cast(animal);
  

Class Cast Exception (Private) — ClassCastException

That is why it is advised to use instanceOf check before downcasting.

• instanceOf

  Used to avoid the ClassCastException by checking if the object belongs to a certain type

  //Example 
  if (animal instanceof Cat) {
      ((Cat) animal).meow();
  }
  
  

  //case 1
  Dog dog = new Dog();
  Animal animal = dog;
  
  if(Cat.class.instanceOf(animal)) -→ false
  
  //case 2
  Cat cat = new Cat();
  Animal animal = cat;
  
  cat.meow();
  
  Cat.class.instanceOf(animal) -→ true