Public static void main

Keyword on data access

• Public
  • Can be accessed anywhere (even other classes)
• Private
  • Can only be accessed in whatever method its in
• Protect
  • Only works with inheritance with methods, still is private but public deeper inside the program

Keyword on variables activity

• Static
• Non-static

Everything we can create classes as objects

Creating our own classes

Splitting up 1 program into different files

Classes look like this

They have 3 parts each

Class name

---

Data States + instance variables

---

Methods (functions/subroutines)

---

Book

---

Data States + instance variables

ID

Static count

---

Static updateBook() (functions/subroutines)

---

Book B = new Book(); //is a constructor, allows us to create instances from a class

Book C = new Book();

B.updateBook();

C.updateBook();

//both B and C objects share the book class, including their methods, but they contain their own data separately,

• static shares methods of the class, not of the objects

Building user defined classes

Each class has 3 parts

//everything can be treated like objects in programming

First is class name: i.e. car dealership db

Second is data and attributes:

String Make

String Model

Int year

//class can contain as much data & attributes as needed

Third part is reserved for methods: //what we do with data

addNewCar()

deleteCar()

printCar()

Going to create separate classes to separate things

The access modifiers and static non-static modifiers

Will use access modifiers

Public

Private

Protected

Default //declaring a method that is like void and prints

• If you make main method private then we cannot even run the program, because its locked off from java running or compiling it

Class car { Public string make Public string model;

private int year; //getters and setters are written in the class where a var is private
public int getYear()//getters always have same data type as var used
{return year;}	

public void setYear(int year) //data type for setters are always void

{ this.year =year;} //this keyword is important in java for set funcs 
                  //this keyword only looks for var being entered for the specific obj

Public void printCarDetails()
{
	println( “Make: “ + make + “\nModel: “ + model + “\nYear: “ + year);
}

~~~~~ code ~~~~~

}

Class Test {

car c = new car(); //doing this initializes space for our new object, the class of car was a data structure but contained 0 data.

c.make = “Lexus”; //can also initialize directly 

c.model = “ES-300H”;

//c.year = 2022; wont work because its private

//because year is private we cant directly access through obj, we need 2 methods to access them, we need getters and setters 

c.setYear(2022);

.println(make: “+ c.make); //public var

.println(“model: “+ c.model); //public var

.println(“year: “ + c.getYear()); //access private var through get method

car d - new car(); //making new obj for this specific car

~~~~~

}

Inside our obj visual

C obj

|Lexus|

|ES-300H|

|2022|

Creating and arrays arraylist, linked-lists of objects

Class Student { Private String name; Private int gpa; Public String getName()

Public int getGPA()
{return gpa;}

Public void setStudent(String name, int gpa)
{
	This.name = name;
	This.gpa = gpa
}

Public void print()
{
	.println(“name: “ + name + “\nGPA: “ + gpa);
}

}

Class Test { Main {

	//Student S = new Student();

	// we dont just 1 student, but we need n amt of students

	// we need to create an array of these objects

	Student [] s = new Student[10]; //if we want 10 students

	//first we create the array, now in each of those fields of array we store data for each student

	Scanner sc = new Scanner(System.in);

	For (int i = 0; i < S.size(); i++)
	{

		.print(“Enter name & gpa of student” + i++);

		String n = sc.next();

		Int g = sc.nextInt();

		//now we have data, next we need to construct our obj in the array

		S[i] = new Student(); //call constructor

		S[i].setStudent(n, g); //store what the user imputed for student i

	}

	//then to print each student

	For ( int i = 0; i < s.size(); i++)

		s[i].print();

}

}

Can create constants like this → Final int MAX = 10;

//Creating the same thing but with a real constructor

Class Student {

Public student(String name, int gpa)
{
	This.name =name;

	This.gpa = gpa;
}

//or

Public student()

{

	this(“null”, 0); //can still use this to pass in params, but by default will set these vals

}

}