Java向下转型(RTTI)

<span style="font-family:Courier New;font-size:14px;">class A {

	protected A process() {

		return new A();
	}

	public String toString() {

		return "A class";
	}

}

class B extends A {

	@Override
	public B process() {

		return new B();
	}

	public void extraMethod() {
	}

	public String toString() {

		return "B class";
	}

}

public class ReturnType {

	public static void main(String[] args) {

		A a = new A();
		B b = new B();
		A c = new B();

		b.extraMethod();

		((B) c).extraMethod();
		((B) a).extraMethod();

	}

}</span>