Two simple questions

Question

29.What is the process called where, at execution time, the type of object to which a variable refers determines the actual method do use. 

30.What keyword must a concrete class use in its declaration to indicate that it provides details on the abstract methods of an interface.

Answer 1

dynamic dispatch determines from the type of the subclass which method should be called, e.g.,

public abstract class Shape {

...

public abstract double area();

...

}

public class Circle extends Shape {

...

public double area();

...

}

...

public Shape sh = new Circle(5);

sh.area();

...

would call the area() method on the instance of class Circle

//----------------------------------------------------------------

abstract classes and concrete classes implement Interfaces

for example

class ArrayList<T> implements interfaces AbstractList<T> and RandomAccess<T>

Answer 2

1. This is a feature of polymorphism and is known as method overloading.
2. the class IMPLEMENTS the interface.