My journey to Java 001 — Variables, operations, methods, object and class

Install Java Development Kit in ubuntu:

IntelliJ IDEA:

1- Variables:

Java variable example:

Create a new java project
The first method, print Hello World!
public static void main(String[] args) {
int int_v = 10; // Integer numbers
double dou_v = 140.13; // floating numbers
char char_v = 'a'; // one character
String str_v = "JourneyToJAva By Islam Taha"; // string

System.out.println(int_v);
System.out.println(dou_v);
System.out.println(char_v);
System.out.println(str_v);

}

2- Operations:

double addition(double x, double y){
return x+y;
}

double subtraction(double x, double y){
return x-y;
}

double multi(double x, double y){
return x*y;
}

double divde(double x, double y){
return x/y;
}

3.1- Methods (Instance Methods):

double addition(double x, double y){
return x+y;
}
\*
type: double (that is the type of the return result)
name: addition
inputs: x and y (both of them are double)
return: x+y (it returns double variable that is why we defined the method with double type)
*\

3.2 Methods (Static Methods):

double static addition(double x, double y){
return x+y;
}

Show me an example for static and instance methods:

//create an object
// class_name object_name = new class_name();
JourneyToJava001 Journey_obj = new JourneyToJava001;
/*
type: class_name
object_name: any_thing
new: deserve a place in the memory to store an object
*/
public class JourneyToJava001 {

double addition(double x, double y){
return x+y;
}
double static subtraction(double x, double y){
return x-y;
}
public static void main(String[] args) {
JourneyToJava001 journey_obj = new JourneyToJava001();
System.out.println(journey_obj.addition(10.1, 10.2));
System.out.println(subtraction(15, 10.2)); }
}

4- Access modifiers:

4.1 — Private

4.2 — protected

4.3 — Default:

4.4 — Public:

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