Reference Variable Casting

This section takes care of Casting(DownCasting and UpperCasting) Downcast: Casting down the inheritance tree to a more specific class

	class Animal {
	void makeNoise() {
	System.out.println("Generic noise");
	}
	}
	class Dog extends Animal {
	void makeNoise() {
	System.out.println("Bark");
	}
	void playDead() {
	System.out.println("Playing");
	}
	}
	public class AnimalTest {
	public static void main(String ...x) {
	Animal a = new Dog();
	Dog d = (Dog)a; // downcast
	a.playDead();
	}
	}

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The compiler trusts in us even if you're trying to cast object that does not refer a dog.

	public class AnimalTest {
	public static void main(String ...x) {
	Animal a = new Animal();
	Dog d = (Dog)a; // downcasting
	a.playDead();
	}
	}

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The code above compiles well but you'll get an exception(java.lang.ClassCastException) at runtime, it occurrs because the compiler only verifies an inheritance tree, in this case Dog is a subtype of Animal. !Important Watch out, the code above compiles the exception is throwns at runtime. Upcasting: Unlike downcasting you don't have to type anything like the previous example Dog d = (Dog)a, the upcasting is implicitly, in other words you're restricting the number of methods that you can invoke.

	class Computer {
	void turnOn() {
	System.out.println("Turning on Computer");
	}
	}
	class MacBook extends Computer {
	void turnOn() {
	System.out.println("Turning on MacBook");
	}
	void openMacX() {
	System.out.println("Openning a MacX");
	}
	}
	public class ComputerTest {
	public static void main(String x[]) {
	MacBook m = new MacBook();
	Computer c = m; // upcasting - implicitly
	Computer c = (Computer)m; //upcasting - explicitly
	}
	}

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Finally the casting can be at one line.

	public class AnimalTest {
	public static void main(String ...x) {
	Animal a = new Dog();
	Dog d = (Dog)a; // downcasting
	a.playDead();
	((Dog)a).playDead(); // at one line
	}
	}

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