This document discusses Java syntax and data types. It covers variable declaration including instance, static, and local variables. It also discusses Java naming rules, comments, primitive data types including integers, floating-point numbers, characters, and booleans. It describes wrapper classes and how autoboxing and unboxing works. It explains promotion and casting. Finally, it provides an overview of common operators in Java like assignment, arithmetic, relational, bitwise, and logical operators.

1. Syntax and Data Type

2. Content
1. Variable declaration
2. Java Naming Rule
3. Comments
4. Primitive Data
5. Type/Wrapper Class
6. Auto Boxing
7. Promotion and Casting
8. Operators

3. Variable Declaration
● Variable is a name of memory location.
● Variable Declaration:
[access_modifier] Datatype varName [ = value];
● There are three types of variables in Java:
○ Instance variable
○ Class Variable or Static variable
○ Local variable

4. Variable Declaration
● Instance variable (non-static fields):
○ Declared outside a method, constructor, block
○ Are visible to all methods, constructors and block in the class
○ No “static” keyword
○ Values are unique to instance of class
○ Has a default value

5. Variable Declaration
● Static or Class variable (static fields):
○ Must be declared outside of methods
○ Has “static” keyword
○ Can be accessed by ClassName.VariableName
○ Has a default value

6. Variable Declaration
● Local Variables
○ Declared in a method, constructor or block
○ No access modifier
○ Lifetime is only within declared block
○ Automatically destroyed once it exits the block
○ No default value => Must be initial a value before used
○ Parameters are also local variables:
■ No access modifier
■ Used for passing a value for method

7. Variable Declaration

8. Java Naming Rules
● Variable is case-sensitive
● Can begin with letter (recommended), dollar sign ($), underscore( _ )
● Can contain letters, numbers, underscores and dollar sign (not recommended)
● Can not contain other special characters, whitespace, keywords
● Should start lowercase and with UPPERCASE for the character of the next word (eg.
teacherName)

9. Comments
● Describe the definition of code
● Remark the code
● Documenting the code
● Get ignored by the compiler
● There are 3 types of comments:
○ Single line
○ Multi line
○ Documents

10. Comments
● Single line : // (Double forward slash)

11. Comments
● Multi-line : /* ................ */

12. Comments
● Documents: /**...............*/

13. Primitive Data Types / Wrapper Class
Primitive Data Types
● Java defines primitive types of data into 8 types: byte, short, int, long, char, float,
double, and boolean
● Primitive Data type is divided into 4 groups:
○ Integer: byte, short, int, long - that are used for whole-valued signed numbers
○ Floating-point numbers: float and double - that is used for decimal numbers
○ Character: char - is represented for symbols in character set such as letters and
numbers
○ Boolean: boolean – is a special data type that is represented true/false values.

14. Primitive Data Types / Wrapper Class
● Integers and Floating-point types
●
●
●
●
● Character

15. Primitive Data Types / Wrapper Class
● Character
○ In Java, char data type has a size of 16-bit that is range from ‘u0000’ to ‘uffff’ or
0-65535
● Boolean
○ boolean data type has 1-Bit size that stores values of 0, 1 represented of false and
true

16. Primitive Data Types / Wrapper Class
Wrapper Class
● provides the mechanism for converting primitive data types to Object Wrapper Class.
● For convert data type from String to primitive data type
● provide some methods for usage

17. Primitive Data Types / Wrapper Class
Wrapper Class

18. Auto Boxing
● Autoboxing is the automatic conversion that Java compiler makes between the
primitive data types and their corresponding object wrapper class
E.g Integer i = 9; // This is autoboxing
// Compiler will replace 9 with Integer.valueOf(9)

19. Unboxing
● Unboxing is the automatic conversion from object wrapper class to primitive data
type
E.g
Integer i = new Integer(9);
int j = i; // This is unboxing
// int j = i; is equal to int j = i.intValue();

20. Promotion & Casting
Promotion
● Promotion is an automatic type conversion
● No data losing
● No casting operator

21. Promotion & Casting
Casting
● Casting is type conversion to a specific data type.
● But there are some points that we can not cast such as:
○ Primitive type to Reference type
○ Null value to primitive type
○ Primitive type to Boolean
○ Boolean to other primitive types

22. Operators
● Operator in java is a symbol that is used to perform operations
● Here are some basic operators that are commonly used:
○ Assignment Operator
○ Arithmetic Operator
○ Relational / Comparison Operator - Bitwise Operator
○ Logical Operator

23. Operators
● Assignment Operators

24. Operators
● Arithmetic Operators

25. Operators
● Relational Operators

26. Operators
● Bitwise Operators

27. Operators
● Logical Operators

28. Thank you!