This document provides an overview of key Java concepts like classes, objects, constructors, arrays, array lists, input/output streams, and call by value vs reference. It begins with explaining what a class is by relating it to real-world entities and their properties and behaviors. It then demonstrates how to define classes, create objects, add methods, and use constructors. The document also covers array lists, input/output streams, and the differences between call by value and call by reference. Videos are provided for further explanation of these topics.

1. The Free Java Course
that doesn’t SUCK
Part 2

2. Saw Part 1?
Part 1 covered all the newbie stuff, search for it J

3. Agenda
1. What is a class & Object
2. Buffered Reader
3. Scanner
4. Array List
5. Call By Value vs. Reference
6. Constructors & Overloading
7. Static keyword

4. Agenda
8. Enumerations
9. Scope vs. Lifetime
10. This keyword
11. Inheritance
12. Method overriding
13. Super keyword
14. Polymorphism

5. Where do I watch these videos?
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6. What is a class?
Simple = Grouping the Java data types to make your own types
Complex = Trying to mock items in the real world…
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7. What is your job?
Take something in the real world and try to represent it in code
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8. 1 What does it have? (Noun)
[Properties]
2 What does it do? What can you do
with it? (Verb) [Methods]
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9. What does it have? (Noun)
[Properties]
Model
Size (Width, height, length, breadth…)
Weight
…
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10. What does it do/you can do?
[Methods]
Call
Sms
Take pictures/videos
Play games
…
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11. 1 What does it have? (Noun)
[Properties]
2 What does it do? What can you do
with it? (Verb) [Methods]
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12. 1 What does it have? (Noun)
[Properties]
Author
Number of pages
Publication name
Title
…
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13. 1 What does it do or you can
do with it? (Verb) [Methods]
Read
Make Notes
…
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14. Ask this question every time…
Take anything in the real world, it can be a real object or a
virtual tank inside your favorite game.
What does it have? What does it do or what can you do with it?
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15. class Phone{
//What does it have? Properties
String model;
double weight;
…
//What does it do or you can do? Methods
public void call(){…};
public void sendSms(){…}
public void takePictures(){…}
public void playGames(){…}
}
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16. class Book{
//What does it have? Properties
String author;
int pages;
String publicationName;
String title;
//What does it do or you can do? Methods
public void read(){…};
public void makeNotes(){…}
}
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17. First Name Last Name Age Occupation Class
Mark Murphy 35
Software
Engineer
Object 1
Jon Skeet 40 Developer Object 2
Frank Underwood 60 Congressman Object 3
Raymond Tusk 65 Entrepreneur Object 4
Zoe Barnes 30 Journalist Object 5
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18. The Conclusion
Class = You create a type
Object = You use your created type
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19. 1. java class vs object
2. Java class vs method
3. Java class vs type
4. Java instance variable
5. Java instance method
6. difference between classes and objects
7. identifying classes and objects in ooad
Google It!

20. How to make a Class?
class Book{
//What does it have? Properties
String author;
int pages;
//What does it do or you can do?
Methods
public int getPages(){…};
public void setPages(int number){…}
}
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21. How to make an Object?
Book one = new Book();
Book two = new Book();
Book mine = new Book();
Book yours = new Book();
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22. When you make an object…
one null
one
Book one;
one = new Book();
one.author = “Herbert Schildt”; one
Herbert
Schildt
author
one.pages = 1000; one
Herbert
Schildt
author
pages = 1000

23. When you make an object…
two null
two
Book two;
two = new Book();
two.author = “J K Rowling”; two
J K
Rowling
author
two.pages = 1500; two
J K
Rowling
author
pages = 1500

24. Adding a method (accessor/getter)
class Book{
String author;
int pages;
public int getPages(){
return pages;
}
}
two
J K
Rowling
author
pages = 1500
int getPages()
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25. Using a method
public static void main(String[] args){
Book two = new Book();
two.author = “JK Rowling”;
two.pages = 1500;
…println(two.getPages());
}
two
J K
Rowling
author
pages = 1500
int getPages()
main()

26. Adding a method (mutator/setter)
class Book{
String author;
int pages;
public int getPages(){
return pages;
}
public void setPages(int number){
pages = number;
}
}
two
J K
Rowling
author
pages = 1500
int getPages()
void setPages(int)
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27. Using a method
public static void main(String[] args){
Book two = new Book();
two.author = “JK Rowling”;
two.pages = 1500;
two.setPages(2000);
…println(two.getPages()) //2000
}
two
J K
Rowling
author
pages = 2000
int getPages()
void setPages(int)
main()
2000

28. Solve this
problem
User will give you length of each side/no of
sides
1 side = Take that as the side of a square or
radius of a circle
2 sides =Length and breadth of rectangle
3 sides= sides of triangle.
Any other number of sides = Invalid Input
Find the smallest, largest and average area.
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29. What do we know from the
problem?
There are 4 shapes : circle, rectangle, square and triangle…
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30. Let’s start with Square
What does a square have?
Length of each side
Diagonal length
Angles
Area
Perimeter
…
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31. Let’s start with Square
What can you do with a square/square do?
Calculate Area
Calculate perimeter
…
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32. 1. What is a getter and setter method?
2. what is accessor and mutator method in java
3. java data members definition
4. java instance method
5. java dot operator
6. where are java objects created
7. java new keyword
Google It!

33. What is a Stream?
0110 1100 1010 1011 0011 0101 1110 1111 0000Data
Source
Your
Program
InputStream
OutputStream
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34. 0 1 0 0 1 0 1 1 0
InputStream
InputStream: Reads only 0s 1s
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35. 0 1 0 0 1 0 1 1 0
InputStream
InputStreamReader
Input
Stream
Reader
H i T h e r e !
Take the binary 0s and 1s from Input Stream and give you characters,
But only 1 character at a time

36. 0 1 0 0
Input
Stream
BufferedReader
Input
Stream
Reader
Wh a t
Take the characters from InputStreamReader and read the entire line
in a single shot…
Buffered
Reader What

37. Need BufferedReader object
BufferedReader reader = new BufferedReader(…);
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38. Need InputStreamReader
InputStreamReader isr = new InputStreamReader(…);
BufferedReader reader = new BufferedReader(isr);
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39. Need InputStream
InputStreamReader isr = new InputStreamReader(System.in);
BufferedReader reader = new BufferedReader(isr);
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40. How do I take input?
…println(“Enter your name”);
InputStreamReader isr = new InputStreamReader(System.in);
BufferedReader br = new BufferedReader(isr);
String yourName = br.readLine();
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41. I a m 2 6 y r
Scanner
Scanner I
Take characters, split everything on the basis of ‘spaces’ by default
am 2 6 y r

42. How does it work?
System.out.println(“Enter whatever you want…”);
Enter whatever you want…
I am 26.5 years old!
Scanner scan = new Scanner(System.in);
I a m 2 6 . 5 y e a r s o l d ! After user hits enter, scanner splits input on the
basis of spaces
I a m 2 6 . 5 y e a r s o l d ! Each part is called a token, scanner has 5 tokens
Use the next() method of the Scanner class to get each token

43. Click to watch videos below
Classes and
Objects
Explained I
Classes and
Objects
Explained II
Classes and
Objects
Example
Take Input
From User
Explained
Take Input
From User
Example

44. 1. what is a stream in java
2. Java InputStream
3. Java OutputStream
4. Java BufferedReader
5. Java Scanner
6. Java Console
7. java scanner ioexception
8. bufferedreader vs scanner vs console
9. Scanner next java
10. Scanner nextLine
Google It!

45. Why Array List?
No need to worry about the size…Also be very specific about
what type of elements you can store
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46. Auto boxing and unboxing
Primitive
Type
Wrapper
Class
byte Byte
short Short
int Integer
long Long
float Float
double Double
char Character
boolean Boolean
Double wrapper = 31.25;
//Putting number into a box = autoboxing
double d = wrapper;
//Removing number from box = unboxing
Doublewrapper =
= 31.25value
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47. How to make one?
ArrayList list = new ArrayList();
//stores anything and everything
ArrayList<String> list = new ArrayList<>();
//stores only Strings
ArrayList<Integer> list = new ArrayList<>();
//stores only Integers
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48. Method
Name
What does it do?
add Adds element to the end of the ArrayList
clear Removes all elements from ArrayList
contains Returns true if ArrayList contains the element you specified, else false
get Returns the element at the index you specify
indexOf Returns index of first occurrence of the element you specified in the
ArrayList
remove Either specify the element and remove it when it occurs first or specify the
index and remove the element at the index
size Number of elements stored
trimToSize Trim ArrayList to current number of elements

49. Lights! Camera! Action!
ArrayList<String> list = new
ArrayList();
list.add(“red”);
list.add(0, “yellow”);
list.add(“green”);
list.remove(1);
list.remove(“green”);
list.contains(“yellow”)
list
list red
list yellow red
list yellow red green
list yellow green
list yellow
true
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50. For each loop
String[] list =new String[10];
…
for(String item : list){
…println(item);
}
ArrayList<String> list = new
ArrayList<>();
…
for(String item : list){
...println(item);
}
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51. Array List References
ArrayList<String> friends = new ArrayList<>();
friends.add(“Anky”);
friends.add(“Gary”);
ArrayList<String> people = friends;
people.add(“Murphy”);
ArrayList<String>
friends =
people =
Anky
Gary
Murphy
0
1
2
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52. Array vs.
Array List
Size of list never changes = use Array
Want a long list of numbers = use
Array
Else use ArrayList
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53. Operation Arrays Array Lists
Get an element e = values[2]; e = values.get(2);
Replace an element values[3] = 12; values.set(3, 12);
Size values.length values.size();
Remove element No inbuilt mechanism values.remove(4);
Initialize fast int[] values = {7, 8, 9}; Call add() 3 times
Arrays vs. Array Lists
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54. 1. java arraylist to array
2. java array to arraylist
3. java arraylist vs array performance
4. java arraylist vs array memory usage
5. java wrapper class
Google It!

55. What is a primitive variable
byte, short, int, long, float, double, char, boolean are primitive
types
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56. Primitive
type
Properties
Not initialized by default.
If reassigned, new value replaces old
byte, short, int. long, float, double &
char have default value 0
boolean has default value false
Stored on stack
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57. What is a reference type
Anything that is not a primitive type…
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58. Reference
Type
Properties
Store addresses
Addresses point to objects
Hence, they refer to objects
Initialized to a default value of null
Can call methods through their object
Stored on heap
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59. Memory Model
…main(){
int i = 20;
String x = “20”;
}
i = 20
x = address
“20”
Stack Heap

60. Call By Value
Don’t modify things like ever!
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61. …modify(int number){
number = 100;
}
…main(String[] args){
int original = 25;
…println(“Before ”+original) //25
modify(original);
…println(“After ”+original); //25
}
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62. original 25
original 25
original 25
original 25
number 25
number 100
int original = 25;
…println(“Before ”+original) //25
modify(original);
…println(“After ”+original); //25
…modify(int number){
number = 100;
}
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63. Call By Reference
Think carefully about what you are doing…
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64. …modify(Square object){
object.side = 100;
}
…main(String[] args){
Square sq = new Square();
sq.side = 25;
…println(“Before ”+sq.side); //25
modify(sq);
...println(“After ”+sq.side); //100
} coursetro.com

65. sq
…main(String[] args){
Square sq = new Square();
sq.side = 25;
…println(“Before ”+sq.side); //25
modify(sq);
...println(“After ”+sq.side); //100
}
…modify(Square object){
object.side = 100;
}
side = 25
sq side = 25
sq side = 100
sq side = 100
object
object
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66. Array List
Explained
Array List
Example
Call by value vs.
reference
Explained
Call by value vs.
reference
Example
Relevant
Videos
Click To Watch Videos Below

67. 1. java call by value vs call by reference
2. java reference variable
3. java object or primitive
4. Stackoverflow error vs outofmemoryerror
Google It!

68. Solve this
problem
User will give you length of each side/no of
sides
1 side = Take that as the side of a square or
radius of a circle
2 sides =Length and breadth of rectangle
3 sides= sides of triangle.
Any other number of sides = Invalid Input
Find the smallest, largest and average area.
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69. 1 What does it have? (Noun)
[Properties]
2 What does it do? What can you do
with it? (Verb) [Methods]
length
breadth
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70. What does it have? (Noun)
[Properties]
Length
Breadth
…
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71. What does it do/you can do?
[Methods]
Calculate Area
Calculate Perimeter
Calculate Diagonal Lengths
…
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72. How to make a Rectangle?
class Rectangle{
//What does it have? Properties
double length;
double breadth;
//What does it do or you can do?
//Methods
public double getArea(){…};
}
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73. How do we initialize stuff?
double bill = 40.35; bill 40.35
Rectangle r = new Rectangle(); r
How to make length = 20, breadth = 10 in the 1st step directly?
length 0
breadth 0
r
length 20
breadth 0
r.length = 20;
r.breadth = 10; r
length 20
breadth 10

74. What are constructors?
Rectangle r = new Rectangle(); That!
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75. The Default Constructor
main()
Rectangle has 2 properties :
length, breadth
Rectangle r = new Rectangle ();
length = 0.0
breadth = 0.0…println(r.length + “ ” + r.breadth)
Square()
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76. Your Default Constructor
main()
Rectangle r = new Rectangle ();
Rectangle(){
length = 20;
breadth = 10;
}
…println(r.length + “ ” + r.breadth)
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77. Your Custom Constructor
Rectangle r = new Rectangle (20, 10);
Rectangle(double l, double b){
length = l;
breadth = b;
}
20, 10
Rectangle r2 = new Rectangle (50, 40);
50, 40
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78. I want both Rectangles!
Rectangle r = new Rectangle();
Rectangle r2 = new Rectangle(20, 10);
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79. Your Overloaded Constructor
Rectangle r = new Rectangle ();
Rectangle(double l, double b){
length = l;
breadth = b;
}
Rectangle r2 = new Rectangle (50, 40);
Rectangle(){
length = 20;
breadth = 10;
}
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80. Rules
Has same name as class
Doesn't return anything EVER!
There is always a default constructor
Unless you make it parameterized
Called before other methods
Called automatically
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81. 1. method vs constructor in java
2. java constructor overloading
3. java default constructor
4. java parameterized constructor
Google It!

82. static
variables blocks methods imports
inner
classes
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83. class Rectangle{
double length;
double breadth;
Rectangle(){
…println(“I was called”);
}
public double calculateArea(){…};
}
Rectangle r = new Rectangle();
//I was called
Rectangle r2 = new Rectangle();
//I was called
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84. How many rectangles?
Keep track of the number of rectangles created…
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85. class Rectangle{
double length;
double breadth;
int count = 0;
Rectangle(){
count = count + 1;
}
public double calculateArea(){…};
}
Rectangle r = new Rectangle();
//1
Rectangle r2 = new Rectangle();
//1
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86. rRectangle r = new Rectangle();
length 0
breadth 0
count 1
r2Rectangle r2 = new Rectangle();
length 0
breadth 0
count 1
The Normal Way
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87. The Static Way
rRectangle r = new Rectangle();
length 0
breadth 0
r2Rectangle r2 = new Rectangle();
r3Rectangle r3 = new Rectangle();
count 1
length 0
breadth 0
length 0
breadth 0
23

88. class Rectangle{
double length;
double breadth;
static int count = 0;
Rectangle(){
count = count + 1;
}
public double calculateArea(){…};
}
Rectangle r = new Rectangle();
//1
Rectangle r2 = new Rectangle();
//2
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89. class Rectangle{
double length;
double breadth;
static int count = 0;
Rectangle(){
count = count + 1;
}
public double calculateArea(){…};
}
…main(String[] args){
...println(Rectangle.count);
}
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90. Static
Variables
Rules
Part of a class not object
ClassName.variableName to access
1 copy maintained across objects of that class
Methods in class can access static variables
Keep common information static
Primitive variables initialized to defaults
Reference static variables initialized to null
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91. Static Blocks
class Rectangle{
…
static int count = 0;
Rectangle(){
count = count + 1;
}
}
class Rectangle{
…
static int count;
static{
count = 0;
}
Rectangle(){
count = count + 1;
}
}
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92. Load
class
Initialize
static
variables
Run
static
blocks
Run
construc
tor
Other
stuff
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93. Static Methods
Methods common to everyone…
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94. r
length 0
breadth 0
r2
r3
length 0
breadth 0
length 0
breadth 0
count 3
int
getCount()
void
setCount(int)
…main(String[] args){
...
main()
println(Rectangle.getCount());
Rectangle.setCount(0);
}

95. What about main?
Static so that JVM can call it using ClassName.main for your
class without objects
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96. Constructors
And Overloading
Explained
Constructors
And Overloading
Example
Static Keyword
Explained
Static Keyword
Example
Relevant
Videos
Click To Watch Videos Below

97. 1. main method static in java
2. java static vs non static
3. Java static vs final
4. java when to use static
5. java static block vs static variable
6. Static block executed before main method
7. static method vs instance method
8. static rules in java
9. when to use static variables in java
Google It!

98. How did I make constants so far?
public class Workday{
static final String MONDAY = “Monday”;
static final String TUESDAY = “Tuesday”;
static final String WEDNESDAY = “Wednesday”;
static final String THURSDAY = “Thursday”;
static final String FRIDAY = “Friday”;
}
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99. How did I use them?
public class Schedule {
//Can be Workday.MONDAY, Workday.TUESDAY…
String workday;
}
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100. What is an enumeration?
A set of related constants…
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101. Example
Direction NORTH, SOUTH, EAST, WEST
Days SUNDAY, MONDAY…
Game Status CONTINUE, WON, LOST
Pizza Sizes SMALL, MEDIUM, LARGE,
EXTRA LARGE
Employee Level INTERN, DEVELOPER,
MANAGER, CEO
Colors RED, GREEN, BLUE…
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102. How to make one
enum PizzaSize {
SMALL,
MEDIUM,
LARGE,
EXTRA_LARGE
};
enum Workday {
MONDAY,
TUESDAY,
WEDNESDAY,
THURSDAY,
FRIDAY
};
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103. How to use one?
class Schedule {
Workday workday;
public Workday getWorkday(){
return workday;
}
public void setWorkday(Workday day){
workday = day;
}
}
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104. Using enumeration with an if condition
if( schedule.getWorkday() == Workday.FRIDAY ) {
...println(“Let’s party guys!”);
}
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105. Using enumeration with switch
switch( schedule.getWorkday() ) {
case MONDAY: case TUESDAY: case WEDNESDAY: case THURSDAY:
…println(“Boring man!”);
break;
case FRIDAY:
...println(“Let’s party guys!”);
break;
}
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106. Printing all the enumeration values
for ( Workday w : Workday.values() ) {
…println(w.name());
}
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107. Add object oriented stuff…
public enum Workday {
MONDAY
TUESDAY
WEDNESDAY
THURSDAY
FRIDAY
final String representation;
Workday (String rep) {
representation = rep;
}
(“Monday”),
(“Tuesday”),
(“Wednesday”),
(“Thursday”),
(“Friday”);
public String getRepresentation() {
return representation;
}
}
for ( Workday w : Workday.values() ) {
…println(w.getRepresentation());
}
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108. Direct Input?
valueOf()… covered in the practical video of this topic.
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109. 1. Why use enums instead of constants
2. java enumeration interface
3. java enumeration methods
4. enumeration vs iterator example in java
5. enumeration name value
6. enumeration ordinal java
Google It!

110. Scope vs. Lifetime
Scope : the region in the program where variable is accessible
Lifetime : the duration that a variable exists
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111. Local Variables
class Test {
public void calculate(){
int x = 10;
for(int i = 1...){
int prod = i * i;
}
}
}
Scope of x = Black box, Scope of i and prod = Green Box, Lifetime = White Box

112. Parameter Variables
class Test {
public static void setA(String t){
…
...println(t);
}
}
Scope = Lifetime = Black Box
Can’t add a local variable and parameter variable with the same name inside a
method
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113. Static Variables
class Test {
static String a = “Test”;
public void display(){
…println(a); //Test
}
public static void setA(String t){
a = t;
}
}
Scope = black box, Lifetime = as long as the program runs
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114. Static Variable Hiding
class Test {
static String a = “Test”;
public void display(){
int a = 20;
…println(a); //20
...println(Test.a); //Test
}
public static void setA(String a){
…println(a); //Parameter’s value
...println(Test.a); //Test
Test.a = a;
}
}
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115. Disjoint Scopes
class Test {
public void square(double number){
double result = …
}
public void cube(double number){
double result = …
}
}
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116. Instance Variables
class Test {
String b = ”Test”;
public void display(){
…println(b); //Test
}
public void setB(String t){
b = t;
}
}
Scope = black box, Lifetime = as long as the object exists
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117. Instance Variable Hiding
class Test {
String b = ”Test”;
public void setB(String b){
…println(b); //prints the parameter’s value
}
}
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118. This Keyword
class Test {
String b = ”Test”;
public void setB(String b){
this.b = b;
}
}
…main(String[] args){
Test one = new Test();
one.setB(“Hi”);
Test two = new Test();
two.setB(“Bye”);
Test three = new Test();
three.setB(“Vow”);
}
b “Test”one
b “Test”two
b “Test”three
this
“Hi”
“Bye”
“Vow”

119. This & constructors
Covered in the practical session J
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120. Enumeration
Explained
Enumeration
Example
This Keyword
and variable
hiding explained
This keyword
and variable
hiding example
Relevant
Videos
Click To Watch Videos Below

121. 1. java this keyword best practice
2. java this static context
3. this vs super in java
4. this keyword constructor java
5. static method this java
6. java this keyword usage
7. java println this
Google It!

122. Without Inheritance
Person
• First Name
• Last Name
• Age
Employee
• First Name
• Last Name
• Age
• Occupation
• Salary
Manager
• First Name
• Last Name
• Age
• Occupation
• Salary
• Department
Managing
Director
• First Name
• Last Name
• Age
• Occupation
• Salary
• Department
• Experience
• Branch

123. Without Inheritance
Vehicle
•Wheels
•Fuel
capacity
•Weight
•Mileage
Bike
• Wheels
• Fuel capacity
• Weight
• Mileage
• Seater
capacity
• Gears
Car
• Wheels
• Fuel
Capacity
• Weight
• Mileage
• Seater
capacity
• Gears
• Type
• Storage
capacity
Truck
•Wheels
•Fuel
Capacity
•Weight
•Mileage
•Seater
Capacity
•Gears
•Type
•Storage
capacity
•Load
capacity

124. Why Inheritance?
Stop repeating yourself, try to find common stuff and declare
them only once…
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125. With Inheritance
Managing Director
Experience Branch
Manager
Department
Employee
Occupation Salary
Person
First Name Last Name Age
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126. With Inheritance
Truck
Load Capacity
Car
Bike
Seater Capacity Gears
Vehicle
Wheels Fuel Capacity Weight Mileage
Type Storage Capacity

127. Solve this
problem
User will give you length of each side/no of
sides
1 side = Take that as the side of a square or
radius of a circle
2 sides =Length and breadth of rectangle
3 sides= sides of triangle.
Any other number of sides = Invalid Input
Find the smallest, largest and average area.
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128. The Shape Hierarchy
Shape
Circle Rectangle
Square
Triangle
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129. Shape and Rectangle
class Shape{
public void display(){
…println(“Displaying shape”);
}
}
s
r
display()
length 0.0
breadth 0.0
display()
sq
display()
length 0.0
breadth 0.0
side 0.0
class Rectangle extends Shape {
double length;
double breadth;
}
class Square extends Rectangle{
double side;
}
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130. Inheritance
Rules
The parent = superclass/base class
The child = subclass/derived class
All fields and methods of superclass are
inherited by subclass
Subclass = specialized version of superclass
Object = direct/indirect superclass for every
class in Java
No multiple inheritance
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131. Object : The
God class
Every class without an extends clause
automatically extends from Object.
toString(), hashcode(), equals(), clone() …
are some of the methods from Object
class
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132. 1. java inheritance types
2. java inheritance example
3. java superclass of all classes
4. java extends multiple classes
5. java extends keyword
6. java subclass vs superclass
7. java subclass override
Google It!

133. What is Method Overriding?
To change what the superclass method does, define it in your
subclass and override it
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134. Shape, Rectangle and Square
class Shape{
public double getArea(){
return 0.0;
}
}
s
r
sq
getArea()
length 0.0
breadth 0.0
getArea()
length 0.0
breadth 0.0
getArea()
side 0.0
returns 0.0
returns 0.0
returns 0.0
s = Shape, r = Rectangle, sq = Square objects
class Rectangle extends Shape {
double length;
double breadth;
}
class Square extends Rectangle{
double side;
}

135. Method Overriding
class Shape{
public double getArea(){
return 0.0;
}
}
s getArea() returns 0.0
s = Shape, r = Rectangle objects
r length 0.0
breadth 0.0
getArea() returns l * b
class Rectangle extends Shape {
double length;
double breadth;
public double getArea(){
return length * breadth;
}
}
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136. Method Overriding
class Rectangle extends Shape {
double length;
double breadth;
public double getArea(){
return length * breadth;
}
}
r
sq
length 0.0
breadth 0.0
getArea()
length 0.0
breadth 0.0
getArea()
side 0.0
returns l * b
returns side * side
r = Rectangle, sq = Square objects
class Square extends Rectangle{
double side;
public double getArea(){
return side * side;
}
}
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137. Difference Between
Overloading
1. Within the Class
2. Different parameters
3. Works with static
4. Compile Time
Overriding
1. With parent child classes
2. Same parameters
3. Doesn’t
4. Run Time
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138. Constructor Chaining
class Shape{
Shape(){
…println(“First”); }}
s First
r
First
Second
sq
First
Second
Third
s = Shape, r = Rectangle, sq = Square objects
class Rectangle extends Shape {
Rectangle(){
…println(‘’Second”); }}
class Square extends Rectangle{
Square(){
…println(‘Third”); }}

139. Super
keyword
Access superclass variable
Call superclass method
Call superclass constructor
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140. How to call superclass variable?
class Shape{
String name = “I am a shape”;
}
s
r
name
name
I am a shape
I am a rectangle
I am a shapedisplay()
s = Shape, r = Rectangle objects
class Rectangle extends Shape {
String name = “I am a rectangle”;
public void display(){
…println(name);
...println(super.name);
}
}
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141. How to call superclass method?
class Shape{
public void display(){
…println(“Which shape?”);
}
}
s
r
display()
display()
Which shape
Which shape
Rectangle
s = Shape, r = Rectangle objects
class Rectangle extends Shape {
@Override
public void display(){
super.display();
…println(“Rectangle”);
}
}
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142. How to call superclass constructors?
class Shape{
Shape ( String name){
…println(name);
}
}
s
r
Shape() …
First
Second
Rectangle()
s = Shape, r = Rectangle objects
class Rectangle extends Shape {
Rectangle(){
super(“First”);
…println(“Second”);
}
} coursetro.com

143. Inheritance
Explained
Inheritance
Example
Super keyword and
Method overriding
Explained
Super keyword and
Method overriding
Example
Relevant
Videos
Click To Watch Videos Below

144. 1. java super keyword
2. java super vs this
3. java super vs override
4. java method overriding rules
5. java method overriding vs overloading
6. accidental overloading java
7. super keyword constructor in java
8. java constructor chaining
9. java static method override
10. java super keyword static
Google It!

145. What is Polymorphism?
Process objects with the same superclass as if they are all
objects of the superclass
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146. A closer look
class Shape{
public double getArea(){
return 0.0;
}
}
class Rectangle extends Shape{
double length;
double breadth;
… //Constructor
public double getArea(){
return length * breadth;
}
}
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147. Superclass variable = Subclass object
class Square extends Rectangle{
double side;
… //Constructor
public double getArea(){
return side * side;
}
}
…main(String[] args){
Square sq = new Square(20);
Rectangle r = new Rectangle(20, 10);
Shape s = sq;
s.getArea(); //400
s = r;
s.getArea(); //200
}
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148. How does it work?
Square sq = new Square(20);
Rectangle r = new Rectangle(20, 10);
Shape s = sq;
s.getArea(); //400
s = r;
s.getArea(); //200
sq
length 0.0
breadth 0.0
getArea()
side 20
r length 0.0
breadth 0.0
getArea()
s
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149. Polymorphism
Properties
1. Access only the superclass
properties/methods when referring
to subclass object
2. Actual object decides which method
is called at run time
3. Type of variable doesn't matter
4. Supports Class & Interface
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150. Solve this
problem
User will give you length of each side/no of
sides
1 side = Take that as the side of a square or
radius of a circle
2 sides =Length and breadth of rectangle
3 sides= sides of triangle.
Any other number of sides = Invalid Input
Find the smallest, largest and average area.
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151. Why should I use this?
Covered in the practical session of this video
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152. Click to watch videos below
Polymorphism
With Classes
Explained
Polymorphism
With Classes
Example

153. 1. java polymorphism example
2. java polymorphism types
3. superclass reference subclass object
4. compile time polymorphism vs runtime polymorphism in
java
5. java polymorphism rules
6. java polymorphism real world example
7. java polymorphism real time example
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154. Thank You From…
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