1. Java Basics
Data Types in Java

2. Data Types in Java Data type tells compiler:
How much memory to allocate
Format in which to store data
Types of operations you will perform on data

3. Data Types in Java Java is a strongly typed language Data types may be
Unlike C, Type checking is strictly enforced at run time
Impossible to typecast incompatible types
Data types may be
Primitive data types
Reference data types

4. Data Types in Java Primitive Numeric Integer int short long byte
Floating point
float
double
Non-numeric
char
boolean
Non-primitive
Arrays
Classes
Interfaces

5. Data Types in Java Primitive Data Types in Java
Integer Data Types
byte
(1 byte)
short
(2 bytes)
int
(4 bytes)
long
(8 bytes)
All numeric data types are signed
The size of data types remain same on all platforms
Char data type is 2 bytes as it uses the UNICODE character set. And so, Java supports internationalization
Floating Data Types
float
(4 bytes)
double
(8 bytes)
Character Data Types
char
(2 byte)
Logical Data types
boolean
(1 bit) (true/false)

6. Integer Data Types in Java
Size in bytes
Minimum Value
Maximum Value
Byte 1
-128
127
Short 2
-32,768
32,767
Int 4
-2,147,483,648
2,147,483,647
long 8
-9,223,372,036,854,775,808
9,223,372,036,854,807

7. Declaration Example int testGrade;
int numPlayers, highScore, diceRoll;
short xCoordinate, yCoordinate;
byte ageInYears;
long cityPopulation;

8. Floating Data Types in Java
Size in bytes
Minimum Values
Maximum Values
Float 4
1.4E-45
E38
double 8
4.9E-324
E308

9. Declaration Example float salesTax; double interestRate;
double paycheck, sumSalaries;

10. Character Data Types in Java
Size in bytes
Minimum Values
Maximum Values
Char 2
Encoded as 0
Encoded as FFFF
One Unicode Character (16 bits - 2 bytes)

11. Declaration Example char finalScore; char newline, tab, doubleQuotes;

12. Logical Data Types in Java
boolean
(1 bit) (true/false)
Used for decision making or as "flag" variables

13. Declaration Example boolean isEmpty; boolean passed, failed;

14. Compatible Data Types Data Type Compatible Data Types byte byte
short byte, short
int byte, short, int, char
long byte, short, int, long, char
float float, byte, short, int, long, char
double float, double, byte, short, int, long, char
boolean boolean
char char

15. Data Types in Java Variables
Variables are defined in Java using the following format :
<access modifier> <type> <variable name>;
e.g. public String name;
private int count;
One value can be placed in one time in a variable but it may change syntax :
dataType identifier; or
dataType identifier1, identifier2, …;

16. Data Types in Java Variables
A named storage in the computer’s memory that stores a value of a particular type for use by program
Example of variable declaration:
The data type can either be:
built-in primitive types (e. g. int, double, char)
Reference data types (e.g. String, BufferedReader)
Naming Convention:
Variable Name: First word lowercase & rest with their initials capitalized (Camel Casing)
e.g. thisIsALongVariableName
DataType
VariableName
int
myAge, cellPhone ;
double
salary ;
char
tempChar ;

17. Data Types in Java Variables (Contd…)
Using primitive data types is similar to other languages
Variables can be declared anywhere in the program
In Java, if a local variable is used without initializing it, the compiler will show an error
int count ;
int max=100;
for (int count=0; count <max; count++) {
int z = count * 10; }
BEST PRACTICE:
Declare a variable in program only when required
Do not declare variables upfront like in C

18. Variable Naming Convention
First letter is lowercase
Embedded words begin with uppercase letter
Name of the variable should be reasonable and meaningful that depict the data store.
Avoid extra large variable name.
Similar Java keyword should not be used as variable name.

19. Assign Value to Variable
Variables
Assignment operator =
Value on the right of the operator is assigned to the variable on the left
Value on the right can be a literal (text representing a specific value), another variable, or an expression (explained later)
Syntax:
dataType variableName = initialValue; Or
dataType variable1 = initialValue1,
variable2 = initialValue2, …;

20. Assign Value to Object Variables Assignment operator =
Value on the right of the operator is assigned to the variable on the left
Value on the right can be a literal (text representing a specific value), another variable, or an expression (explained later)
Syntax:
dataType variableName = initialValue; Or
dataType variable1 = initialValue1,
variable2 = initialValue2, …;

21. Data Types in Java Comments in Java
A single line comment in Java starts with //
A multi line comment starts with /* & ends with */
// This is a single line comment in Java
/* This is a multi line
comment
in Java */

22. Data Types in Java Reference Data Types
Hold the reference of dynamically created objects which are in the heap
Can hold three kinds of values:
Class type: Points to an object / class instance
Interface type: Points to an object which is implementing the corresponding interface
Array type: Points to an array instance or “null”
Difference between Primitive & Reference data types:
Primitive data types hold values themselves
Reference data types hold reference to objects, i.e. they are not objects, but reference to objects
Objects & Arrays are accessed using reference variables in Java
A reference variable Is similar to a pointer (stores memory address of an object)
Java does not support the explicit use of addresses like other languages

23. Data Types in Java Reference Data Types (Contd…)
Java does not allow pointer manipulation or pointer arithmetic
Memory Representation:
primitive
reference
A reference type cannot be cast to a primitive type
A reference type can be assigned ‘null- to show that it is not referring to any
int primitive = 5;
String reference = “Hello” ; 5
Hello

24. Data Types in Java Typecasting Primitive Data Types
Automatic type changing is known as Implicit Conversion
- A variable of smaller capacity can be assigned to another variable of bigger capacity
Whenever a larger type is converted to a smaller type, we have to explicitly specify the type cast operator
This prevents any accidental loss of data
int i = 10;
double d;
d = i;
double d = 10;
d = i;
i = (int) d;
Type cast operator ()

25. Access Modifier
A modifier is a keyword placed in a class, method or variable declaration that changes how it operates.
There are basically four types of access modifier in JAVA
public
private
default
protected

26. Default Modifier
If a class has no modifier (the default, also known as package-private), it is visible only within its own package (packages are named groups of related classes.

27. Public Modifier
A class may be declared with the modifier public, in which case that class is visible to all classes everywhere.
The following function uses public access modifier:
Example :
public static void main(String[] arguments) {
/ // ... }

28. Private Modifier
The private modifier specifies that the member can only be accessed in its own class.
Example:
public class football{
private String score;
public String getScore() {
return this.score; }
public void setScore(String score) { this.format = format;

29. Protected Modifier
The protected modifier specifies that the member can only be accessed within its own package (as with package-private).
Example:
class AudioPlayer {
protected boolean openSpeaker(Speaker sp) {
// implementation details }
} class StreamingAudioPlayer {
boolean openSpeaker(Speaker sp) {

30. Protected Modifier
Here, if we define openSpeaker() method as private, then it would not be accessible from any other class other than AudioPlayer. If we define it as public, then it would become accessible to all the outside world. But our intension is to expose this method to its subclass only, that's why we used protected modifier.

31. Sample Exercise #1 Is it legal to assign a char to an int variable ?
Yes, it is possible
int i = ‘a’; // assigns 97 to I

32. Sample Exercise #2 Is it legal to assign an int to an char variable ?
Yes, it is possible
char c = 97; // assigns ‘a’ to c

33. Sample Exercise #3
It is possible to perform arithmetic on char variables ?
Yes, it is possible
char ch = ‘a’;
ch = ch + 1; // assigns ‘b’ to ch

34. Sample Exercise #4
Does a int value can be assigned to a char type variable ?
Yes, we can assign a integer value to a char type variable but a char type value cannot be assigned to a int type variable