Java Syntax Basics

Java Syntax Basics

1. Key words

Some words have special meanings to the compiler and cannot be used as identifiers, all lowercase letters

Java language keywords

Abstract	Boolean	Break	Byte	Case	Catch	Char	Class	Try	Do
Default	Continue	Double	Else	Extends	Assert	Final	Finally	Float	For
If	Implement	Import	instanceof	Int	Interface	Long	Native	New	Goto
strictfp	Package	Private	protected	public	return	Short	static	void	Switch
This	Synchronized	Throw	Throws	Transient	Const	Super	Volatile	While

Three reserved characters: Goto, FALSE, NULL

Main is a special name used to describe the starting method of a Java program, but it is not a keyword

2. Identifiers

Naming rules: can only be numbers, letters, underscores, $

Cannot start with a number

Strictly case-sensitive

cannot be a keyword

3. Data type

Basic data type:

Data type	Key words	Size
BYTE type	Byte	8 Guests
Short-integer	Short	16 Guests
Integral type	Int	32 Guests
Long integer type	Long	64 guests
Single-precision	Float	32 Guests
Double-precision Type	Double	64 guests
Character type	Char	16 Guests
Boolean type	Boolean	Not sure, determined by the JVM

Reference type: Class, interface, array

The difference between a reference type and a base type: The reference does not contain the actual data of the object it points to, but instead points to the location of the object in memory.

Basic types of variables, Java virtual machines put them in the Java stack

A variable of a reference type, the reference type itself is placed in the Java stack, and the object pointed to by the reference is placed in the Java heap

4. Variables

Data type variable name

For example: int A;

Assignment method: 1.int a = 3;

2.int A;

A = 3;

5. Constants

Use the final keyword in Java to indicate that a variable is actually a constant

Programmers often capitalize all the letters of a constant

6. Operators

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	&, |, ^
Condition And,or	&&, | |
Trinocular operator	?:
Assignment operators	=
Extended assignment operators	*=,/=,%=, + =,-=, <<=, >>=, >>>=, &=, ^=, |=

7. Comments

Single-line Comment: Peer text with two forward slash "//" comment out Slash

Multiline Comment: the "/*" and "* *" symbols are used for comments on multiple lines of code. Open the comment with "/*" and "*/" to close the comment. So the text will be commented out between the two.

Javadoc notes: "/**" and "* *" are a pair of special types of annotation symbols that are used with the Javadoc tool to generate HTML files that contain comments. These generated HTML pages are provided to the programmer along with the Java code to help the programmer understand the purpose and usage of the code. In Java, this feature is widely used.

Java Syntax Basics