Java basic grammar

An article released exclusively on October 09, 2017. I referred to "** Introduction to Java that can be understood clearly **".

Construction of development environment

Java SE from Oracle, IntelliJ from JET BRAINS DL and install IDEA. The Atom editor is also useful.

Basic matters

Variable declaration

`Main.java`


public class Main{
    public static void main(String args[]){
int variable name=value;
final int constant name=value; //Constant name is uppercase
    }
}

Classification	Model name	Stored data
integer	long	Big
	int	usually
	byte	-128 ~ 127
Decimal	double	usually
	float	ambiguous
Boolean value	boolean	true / false
letter	String	String
	char	One character

operator

`Main.java`


int age = 15;

operator	function	Evaluation direction
++	Left side=Left side+ 1	->
--	Left side=Left side- 1	->
*	Multiply	->
/	division	->
%	Surplus division	->
+	Addition	->
	String concatenation	->
-	Subtraction	->
=	Substitution	<-
+=	Left side=Left side+right side	<-
	"Left side" = "Left side" + "right side"	<-
-=	Left side=Left side-right side	<-
*=	Left side=Left side*right side	<-
/=	Left side=Left side/right side	<-
%=	Left side=Left side%right side	<-

Basic instruction execution

`Main.java`


//Screen output(With line breaks)
System.out.println("String");
//Screen output(No line breaks)
System.out.print("String");
//Convert strings to numbers
int n = Integer.parseInt(String);
//Random number generation
int r = new java.util.Random().nextInt(upper limit);
//Input reception from keyboard
String m = new java.util.Scanner(System.in).nextLine();
int n = new java.util.scanner(System.in).nextInt();

Conditional branch

operator

operator	meaning
==	Left side=right side
!=	Left side ≠ right side
>	Left side>right side
<	Left side>right side
>=	Left side ≧ right side
<=	Left side ≤ right side
&&	Conditional expression 1 ∨ Conditional expression 2
\|\|	Conditional expression 1 ∧ Conditional expression 2

If-ElseIf-Else Statement --Branch Branch

`Main.java`


if (Conditional expression 1) {
Block 1
} else if(Conditional expression 2) {
Block 2
} else {
Block 3
}

Switch statement

When evaluating ** a match between the left and right sides of ** integers, strings, and characters **, the If-ElseIf-Else statement can be rewritten as a Switch statement.

`Main.java`


switch(Condition value)　{
case value 1:
Process 1
case value 2:
Process 2
        break; //Suspend the process itself
    default:
Default processing
}

Do-While Statement-Repeat

`Main.java`


do{
block
}while (Conditional expression) {
block
}

For statement

You should use a For statement when you know the number of iterations.

`Main.java`


for (int i = 0; i < 10; i++) {
block
    if (i == 7) {
        continue; //Cancel the current lap
    }
}

while (true) {
block//infinite loop
    for (;;) {
block//infinite loop
    }
}

Array

`Main.java`


int[]Array name= {Value 0,Value 1...Value n}
Array name= null; //Cut the array
Number of elements in int array=Array name.length;

//Extended For statement
for(int arbitrary variable name:Array name) {
block
}