Question

1.     When a sub class object is created, when is the call to the super class constructor made? How does a programmer call the super class constructor from the sub class?

What do all classes indirectly extend?
What methods does every class inherit from the Object class?

2.     When writing methods in a sub class, how can those methods call the methods from the parent class?

3.     Which class is more specific, a super class or a sub class?

4.     Can a super class have more than one sub class? What is an abstract class?

5.     Can an abstract class be instantiated?
Can an abstract class be used as a super class?

6.     If a class extends a superclass as follows: public class ClassA extends ClassParent Is the following a valid statement:

7.     ClassParent objectA = new ClassA( ); Is the following a valid statement?

8.     ClassA objectB = new ClassParent( );

9.     What is the difference between overriding a method and overloading a method?

10. Polymorphism

11. How does the JVM know which method to call when an object invokes a method? What is the purpose of the instanceof operator?
12. What data type does the instanceof operator evaluate to?
13. What is typecasting?

14. Protected and package specifiers

15. List the four Java access specifiers in order of least restrictive to most restrictive.

16.If you do not code an access specifier for a field or method, what is its default access?

17. Java interfaces

18. What code is contained in a Java interface?

19. All the method headings in a Java interface must have this access:
20. All the fields in a Java interface are: _________, _____________, and ___________. How many interfaces can a class implement?
21. What is meant by implementing an interface?

Answer 1

1.Whenever a subclass object is created then the parent class default constructor will be called first followed by subclass constructor.

A super class parametrized constructor can be called by its subclass using super keyword as the first line in subclass constructor.

All classes extend the object class.

The methods which all the classes inherit from object class are clone(),equals(),finalize(),toString(),hashCode(),getClass()

2.Super keyword is used to call superclass methods from the childclass.
3.A superclass is more specific as it has all the attributes clearly defined which its childclasses need to extend.
4.Yes , a subclass can have more than one subclass.An abstract class is one which cannot be instantiated.
5.No, it cant be instantiated.Yes, it can be used as a superclass.
6.Yes
7.Yes it is a valid statement.
8.No, it is not a valid statement.
9.Overriding means having same method name in superclass and childclass whereas overloading means having same method name for more than one method
in same class but different number of parameters.
10.Polymorphism is ability of object to take on many forms.If an object passes more than one IS a test it is polymorphic.Most common example is parent class
reference with child class object.
11.JVM makes use of dynamic binding for instance methods and static binding for static methods to determine which method to call.
12.boolean datatype
13.Typecasting means converting from one datatype to other.
14.protected and package specifiers are used to limit the accessibility of classes.
15.public,default,protected,private.
16.Default
17.Interface is a collection of abstract methods.
18.Abstract methods,default methods,static variables etc.,
19.public
20.public,static and final.A class can implement multiple interfaces at once.
21.Implementing an interface means implementing all the methods present in the interface.