InitialTest.java

Java Programming Fundamentals
1. What is Java?

Java is an object-oriented programming language (OOP).

Object-oriented programming organizes code using:

Classes
Objects
Variables (data)
Methods (behaviors/functions)
2. Classes and Objects
Class

A class is a blueprint for creating objects.

Example:

Java
public class SayHello {
}

The filename and public class name must match.

Example:

Plain Text
File: SayHello.java
Class: public class SayHello
 
Object

An object is an instance of a class.

Objects contain:

Variables (data)
Methods (behavior)

Example:

Java
SayHello speaker = new SayHello();

new creates a new object.

Object-Oriented Programming (OOP)

OOP is based on creating objects that contain both data and behaviors.

Example:

Java
public class Dog {
 
String name;
 
void bark() {
System.out.println("Woof!");
}
}

Here:

name is data
bark() is behavior
3. Variables and Data Types
Variables

Variables store information in memory.

Example:

Java
int age = 20;
String name = "John";
Primitive Data Types
Boolean

Stores:

Java
true
false

Example:

Java
boolean lightOn = true;
Integer (int)

Stores whole numbers.

Java
int x = 10;
int y = -5;
Floating Point Numbers

Store decimal values.

Java
float price = 3.99f;
double pi = 3.14159;
4. Integer Division

When two integers are divided, the decimal portion is discarded.

Example:

Java
int x = 5 / 2;

Result:

Java
x = 2

Because both values are integers.

5. Methods

A method is a function inside a class.

Example:

Java
public void sayHello() {
System.out.println("Hello");
}
Method Parameters

Methods can accept inputs called parameters.

Example:

Java
public int add(int a, int b) {
return a + b;
}

Call the method:

Java
int result = add(7, 8);
Return Values

A method can have many parameters:

Java
add(1, 2, 3);

but can only return one value:

Java
return result;
6. Understanding Main()

Every Java application starts with:

Java
public static void main(String[] args)

This is called the main method.

Java begins running your program here.

Example:

Java
public class Main {
 
public static void main(String[] args) {
System.out.println("Program Started");
}
}
7. Understanding public static void
public

The method can be accessed from anywhere.

static

The method belongs to the class itself.

You do not need to create an object to use it.

Example:

Java
Math.abs(-5);

No object needed.

void

The method returns nothing.

Example:

Java
public void sayHello() {
System.out.println("Hello");
}

No value is returned.

8. System.out.println()

Example:

Java
System.out.println("Hello");
 

Breakdown:

System

A built-in Java class.

out

A predefined output object.

println()

A method that prints text to the screen.

The dot (.) operator accesses members of classes and objects.

9. The Dot Operator

The dot operator accesses:

Variables
Methods

Examples:

Java
speaker.adder();
Java
speaker.name;
10. Creating and Using Objects

Example class:

Java
public class SayHello {
 
int a;
int b;
 
int adder() {
return a + b;
}
}

Creating objects:

Java
SayHello speaker1 = new SayHello();
SayHello speaker2 = new SayHello();

Assigning values:

Java
speaker1.a = 5;
speaker1.b = 10;
 
speaker2.a = 8;
speaker2.b = 15;

Using methods:

Java
int result1 = speaker1.adder();
int result2 = speaker2.adder();

Results:

Java
result1 = 15
result2 = 23

Each object stores its own data.

11. Loops
For Loop

Used when repeating the same code multiple times.

Example:

Java
for(int i = 0; i < 5; i++) {
System.out.println(i);
}
Parts of a For Loop
Java
for(initialization; condition; update)

Example:

Java
for(int i = 0; i < 5; i++)

Initialization:

Java
int i = 0

Condition:

Java
i < 5

Update:

Java
i++
Increment Operator
Java
i++;

Means:

Java
i = i + 1;
12. State-Based Programming

A state is a distinct mode or condition that a program can be in.

Examples:

On
Off
Idle
Running
Menu Screen
Game Over Screen
Light Switch Example

State 0 = On

State 1 = Off

Java
int state = 0;
Switch Statement
Java
switch(state) {
 
case 0:
 
light = true;
 
if(button == true) {
state = 1;
}
 
break;
 
case 1:
 
light = false;
 
if(button == true) {
state = 0;
}
 
break;
}
Why State Machines Are Useful

Instead of writing huge nested if statements:

Java
if(...)
{
...
}
else if(...)
{
...
}
else if(...)
{
...
}

States keep complex systems organized and easier to understand.

13. Toggle Logic

A boolean can be flipped using !.

Example:

Java
light = !light;

If:

Java
light = true

Then:

Java
light = false

and vice versa.

This is called toggling.

14. Break Statement

break immediately exits the current switch case or loop.

Example:

Java
case 0:
System.out.println("ON");
break;

Without break, Java continues into the next case.

This is called fall-through.

15. Event-Based Programming

Event-based programming means code runs when something happens.

Examples of events:

Button click
Mouse click
Key press
Timer expiration

Example:

Java
button.addActionListener(e -> {
System.out.println("Button Clicked");
});

The program waits for events and responds when they occur.

Quick Exam Review
Plain Text
Class = Blueprint for objects
 
Object = Instance of a class
 
Method = Function inside a class
 
Variable = Stores data
 
int = Whole number
 
float/double = Decimal number
 
boolean = true or false
 
main() = Program starting point
 
public = Accessible from anywhere
 
static = No objpublic class InitialTest {
    public static void main(String[] args){
        System.out.println("You're ready to program in Java!");
    }
}