inheritence

Question 1

what is inheritance

Answer 1

first a very general class is defined
then more specialized versions of the class are defined
   - you can then add new instance vars and methods
   - this class can inherit the methods and instance vars of the general class

Inheritance is the process by which a new class is created from another class
–The new class is called a derived(child) class, subclass, specialized class 
–The original class is called the base(parent) class, super class, generalized class - superscript used for super class

Question 2

why is inheritance great

Answer 2

allows code to be reused without having to copy it into the definitions of derived classes

Question 3

format of class drawings for inheritance

Answer 3

top class - superclass

Question 4

how to create derived classes

Answer 4

extends baseclass
public class HourlyEmployeeextends Employee{
    /*new instance variables*/
}

Question 5

what does the derived class automatically inherit from the parent class

Answer 5

instance vats
all static vars
all public methods

*private instance variables cannot be changes without using the set and get methods that should be found in the parent class

Question 6

what does it mean to override a method definition

Answer 6

you can change or override an inherited method if needed
–In order to override a method definition, a new definition of the method is simply placed in the class definition, just like any other method that is added to the derived class

Question 7

can you change the return type of an overriden method?

Answer 7

when overriding a method the returned type may be changed to any descendent of the returned type - known as a covariant return type

Question 8

can you change the access permission of an overridden method

Answer 8

valid:
base class: private void doSomething()
derived class: public void doSomething()

invalid:
base class: public void doSomething()
derived class: private void doSomething()

A subclass can make something more visible, but not less visible

Question 9

overriding vs overloading

Answer 9

When a method is overridden, the new method definition given in the derived class has the exact same number and types of parameters as in the base class
•When a method in a derived class has a different signature from the method in the base class, that is overloading

Question 10

what does the final modifier do?

Answer 10

final public void somemethod() --> this method cannot be redefined in any derived class
final class --> no subclasses of this class can be made...ever

Question 11

what is the super constructor?A

Answer 11

a derived class uses a constructor from the base class to initialize all the data inherited from the base class

public derivedClass(int p1, int p2, double p3)  {
super(p1, p2);
instanceVariable = p3;}

–In the above example, super(p1, p2); is a call to the base class constructor
- calling super must be the first step in the constructor definition

Question 12

what happens if the base class doesn’t use super in the constructor definition?

Answer 12

then the no-argument constructor of the base class will automatically be invoked–This can result in an error if the base class has not defined a no-argument constructor
- you cannot use multiple supers i.e. super.super.tosString()

Question 13

how to use an original method in a derived class

Answer 13

super.someOrigMethod() - the grandchild class goes to the parent and the parent will have a reference to all the methods in the grandparent class

Question 14

what does instanceof do?

Answer 14

checks if an object is of the type given as its second argument - will return true if the object is the type of any descendant of classname

Question 15

what does getClass do?

Answer 15

if two objects were created with the same class?

Checks to see if the classes are exactly the same
E.g. if one is technical and one is engineer, even though engineer is technical it will return false because they arent exactly the same
Returns a number when used in another way

Question 16

what happens when you leave out the modifier?

Answer 16

you get package access

Question 17

what is package access?

Answer 17

Instance variables or methods having package access can be accessed by name inside the definition of any class in the same package–However, neither can be accessed outside the package

Question 18

what is protected access?

Answer 18

can be accessed by name: inside own class def, inside any derived class, in the definition of any class in the same package