Module 3 - Java Basics

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2026-02-26 16:01

Tags: #java

Author: Duke Hsu

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Module 3 - Java Basics

Module Topic

Data Types

• Variables

• Data Types

• Constants

Operators and Expressions

• + - * / .....

Scanner

• Input

• Output

• nextLine()

Example Application in OOP

Datatypes and Variables and Constants

Concept Define

• Variables are named memory locations used to store data that can change during program execution.

• Data Types define the type and size of data a variable can store.

• Constants are values that cannot be changed once assigned . In Java, constants are declared using the final keyword.

Primitive Data Types in Java

DATA TYPE	DESCRIPTION	EXAMPLE	DEFAULT VALUE (FOR FIELDS)
byte	very small whole numbers	byte b = 10;	0
short	small whole numbers	short s = 100;	0
int	whole numbers	int age = 18;	0
long	very large whole numbers	long follows = 9888222333L;	0L
float	decimal numbers(single precision)	float price = 99.5f	0.0f
double	decimal numbers (double precision)	double salary = 25000.78;	0.0d
char	a single charater	char grade ='A';	'\u0000'
boolean	true of false values	boolean isPassed = true;	false

Note

String or any Object default values is NULL

Operators

1. Arithmetic Operators

   • Used to perform mathematical operations.

2. Assignment Operators

   • Used to assign values to variables

3. Relational (Comparison ) Operators

   • Used to compare two values and return a boolean result

4. Logical Operators

   • Used to combine of negate boolean conditions, allowing for complex decision-making in control flow statements.

5. Unary Operators

   • Unary operators in java perform operations on a single operand. They include operations likenegation(-),increment(++), and decrement(--), allowing for modifications or evaluations of a single value.

6. Ternary(Conditional ) Operator

   • The ternary operator in java is a concise way to evaluate a condition and return one of two values based on that condition. It uses the syntaxcondition ? valueIfTrue : valueIfFalse, enabling shorthand conditional expressions.

Tables and Example

Arithmetic

OPERATOR	DESCRIPTION	EXAMPLE
+	addition	a + b
-	subtraction	a - b
/	division	a / b
%	modulus(remainder onec)	b % a
*	multiplication	a * b

Assignment

OPERATOR	EXAMPLE	MEANING
=	x = 5	assign 5 to x
+=	x += 2	x = x + 2
-=	x -= 1	x = x - 1
*=	x *= 3	x = x * 3
/=	x /= 2	x = x / 2

Relational (Comparison)

OPERATOR	DESCRIPTION	EXAMPLE
==	equal to	x == y
!=	not equal tp	x != y
>	greater than	a > b
<	less than	b < a
>=	greater than or equal to	c >= b
<=	less than or equal to	c <= a

Logical Operators

OPERATOR	DESCRIPTION	RETURN
&&	AND	all true return true
||	OR	if one is true , then true
!	NOT	true / false

Unary Operators

OPERATOR	DESCRIPTION	RETURN
+	Unary plus operator	indicatespositive value (numbers are positive without this, however)
-	Unary minus operator	negates an expression
++	Increment operator	Increments a value by 1 (遞增)
--	Decrement operator	decrements a value by 1 (遞減)
!	Logical complement operator	inverts the value of a boolean(反轉)

int a = 5;
int nagetiveA = -a;  //nagetiveA output -5 unary minus operator

int b = -5;
int B = +b;  // B out put -5 , unary plus operator ,

int c = 6;
c++; //c is 7

int d = 10;
d--;  // d is 9

boolean trueThings = false;
boolean notrue = !trueThings; //'nottrue' is now true

Ternary (Conditional) Operator

Syntax: condition ? valueTrue : valueFalse

int age = 18;

String status = (age>=18)? "Adult" : "Minor"; // true , output adult

More Operator plz check : https://docs.oracle.com/javase/tutorial/java/nutsandbolts/opsummary.html

Order of Precedence(Highest to Lowest)

PRECEDENCE LEVEL	OPERATORS	OPERATOR CATEGORY
1 (Highest)	()
2	++, --,!	Unary Operators
3	*, /, %	Arithmetic
4	< , > ,<=, >=	Relational (Comparison)
5	== , !=	Relational (Comparison)
6	&&	Logical Operators
7	`
8	= , +=, -= , *= , /=	Assignment

Input and Output Using Scanner

The Scanner Class

• The Scanner class is part of the java.util package, and allows programs to accept input from users.

Common Scanner Methods.

• nextlnt() : Reads the next integer input from the user. For example, if the user enters "42", it stores 42 as an integer.

• nextDouble(): Reads the next double (decimal) number input. For instance, if the user enters "3.14", it stores 3.14 as a double.

• nextLine(): Reads an entire line of text input, including spaces, until the user presses Enter. For example, if the user enters "Hello World", it stores "Hello World" as a string.

• nextBoolean(): Reads the next input value as a boolean (true or false). If the user types "true" or "false", it stores that value as a boolean.

• next(): Reads the next token (word) until white space.

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References

Module 3 - OOP Java Basics.pdf

Summary of Operators - https://docs.oracle.com/javase/tutorial/java/nutsandbolts/opsummary.html

Scanner - java platform -https://docs.oracle.com/javase/8/docs/api/java/util/Scanner.html

Java Data Types - https://www.geeksforgeeks.org/java/java-data-types/