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

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


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

//Screen output(With line breaks)
//Screen output(No line breaks)
//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(;
int n = new java.util.scanner(; 

Conditional branch


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

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.

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

Do-While Statement-Repeat

}while (Conditional expression) {

For statement

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

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

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


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) {

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