Java Basic syntax

1. Keywords

Boolean, break, Byte, case, Char, class, continue, default, do, double, else, final, float, For,goto, if, import, int, Lon G, new, package, private,protected, public, return, short, static, switch, this, void, while, abstract, catch, const, exte NDS, Assert, finally, implements, instanceof, interface, native, STRICTFP, Super, Synchronized,throw, throws, transient, t RY, volatile

2. Reserved words

True, FALSE, NULL

3. Identifiers

Naming rules: A. Identifiers can contain letters, numbers, underscores, dollar signs

B. Identifiers cannot be keywords or reserved words

C. Identifiers cannot begin with a number

D. Identifiers are case-sensitive and do not specify a maximum length

For example: identifier, user_name, _sys_varl, $change, etc.

Naming conventions: A. " "(Choose concise English words as identifiers)

B. Each word starts with a lowercase letter, the first letter of the second word is capitalized or the first letter of each word is uppercase (camel-named)

For example: Mystudentcount, Databaseuser

c. Words are not separated by a space break or connection number (-), the bottom line (_), the first letter of each word (Pascal nomenclature)

For example: FirstName, UserName

4. Data type

Base data type: Numeric (Integer (Byte, short, int, long), float (float, double)), character (char), Boolean

Reference types: Class, Interface (interface), arrays, strings (string)

Note: Strings are denoted by double quotation marks for character literals, such as "A", which declares strings with string name;

"+" in the string to connect the literal

Table-java Basic data types

Data type	Key words	Size
BYTE type	Byte	1 bytes (8 bits)
Short-integer	Short	2 bytes (16 bits)
Long integer type	Long	8 bytes (64 bits)
Single-precision	Float	4 bytes (32 bits)
Double-precision Type	Double	8 bytes (64 bits)
Integral type	Int	4 bytes (32 bits)
Character type	Char	2 bytes (16 bits)
Boolean type	Boolean	Not sure

Note: The Boolean value is True, False

5. Constants

Final data type constant name = constant value;

For example: Final double PI = 3.14159;

6. Casting

The cast operator consists of a data type of a strong conversion that is placed in parentheses. （）；

When a numeric data expression performs a calculation, an automatic type conversion is performed from low precision to high precision, that is, byte < short < int < long < float < double.

For example: int x;

Double d = 3.5;

x = D; cannot be compiled by

x = (int) d; can be compiled by

Escape character for 7.Java

\b: Backspace

\ t: Tab

\ n: Line break

\ r: Enter

\ ": Double quotation marks

\ ': Single quote

\ \: Back slash

8. Operators

Operators and Precedence in Java

Operator classification	operator
Pre-or post-increment/decrement	+ + 、--
Unary operators	+ 、-、 ~,! , (CAST)
Multiplication/Division/Modulus	*、/、%
Add/subtract/String connections	+ 、-、 +
Shift Operators	<<, >>, >>>
Comparison operators	<, <=, >, >=, instanceof
Equality operators	= =,! =
Bitwise operators	&, |, ^
Conditions and, or	&&, | |
Trinocular operator	? :
Assignment operators	=
Extended assignment operators	*=,/=,%=, + =,-=, <<=, >>=, >>>=, &=, ^=, |=

A. Increment and decrement operators

A. Pre-increment

For example: int x = 5;

int z = ++x;

Output: x = 6 z = 6;

B. Post-increment

For example: int x = 5;

int y = x + +;

Output: x = 6 y = 5;

B. Three-mesh operator

Syntax form: (Boolean expression)? x:y;

For example: (x = = 5)?   "Yes": "No"; If x equals 5, then "Yes" is displayed, otherwise "no" is displayed.

Using the If/else statement: if (x = = 5) {

SYSTEM.OUT.PRINTLN ("yes");

}else{

System.out.println ("no");

}

9.Java comments

Single-line Comment://

Multi-line Comment:/*......*/

Text/Document notes:/**......*/(primarily written on a class or method)

Java Basic syntax