Since I started studying Java, I will leave what I learned.

Output

System.out.println("Hello World!");
System.out.println(123);

//Execution result
//Hello World!
//123

Output in () and start a new line. How to read println is print line. I tried to find out what System and out mean, but for now I decided not to go deep. Reference) Understand System.out.println ("hello, world")

Variable declaration

int number; //Declare variable number of type int
String str; //Declare a variable str of type String

Variable initialization

int number = 5;
String str = "hoge";

Assign a value at the same time as the variable is declared.

Variable calculation, concatenation

//Calculation of int type variables
int number1 = 3;
System.out.println(number1 + 5);   //The result is 8
int number2 = 10;
System.out.println(number1 + number2);   //The result is 13

//Concatenation of String type variables
String greeting = "Good morning";
System.out.println(greeting + "sky");   //おはようsky
String name = "Riku";
System.out.println(greeting + name);   //Good morning Riku

Self-substitution

x = x + 10;   //Add 10 to the variable x and overwrite

There are basic and abbreviations for the description method.

Uninflected word	Abbreviation
x = x + 10	x += 10
x = x - 10	x -= 10
x = x * 10	x *= 10
x = x / 10	x /= 10
x = x % 10	x %= 10

When adding and subtracting only 1

There are also abbreviations.

Uninflected word	Abbreviation	Further omitted
x = x + 1	x += 1	x++
x = x - 1	x -= 1	x--

double type

There are several data type variables that handle values other than int type. Reference) Java Road: Variables (1. Variables) The double type handles values with a decimal point.

double number = 3.14;
System.out.println(number);   ///The result is 3.14

Studying Java ①