java basic writing standards

Table of contents

basic grammar

Java identifier

The difference between Java source program and compiled execution

Basic template (Hello World program)

public class HelloWorld {
    /* 第一个Java程序
     * 它将输出字符串 Hello World
     */
    public static void main(String[] args) {
        System.out.println("Hello World"); // 输出 Hello World
    }
}

basic grammar

Case-sensitive: Java is case-sensitive, which means that the identifiers Hello and hello are different.
Class name: For all classes, the first letter of the class name should be capitalized. If the class name consists of several words, the first letter of each word should be capitalized, for example MyFirstJavaClass .
Method name: All method names should start with a lowercase letter. If the method name contains several words, the first letter of each subsequent word is capitalized.
Source file name: The source file name must be the same as the class name. When saving the file, you should use the class name as the file name (remember Java is case-sensitive), and the file name suffix is .java . (If the file name and class name are different, a compilation error will occur).
Main method entrance: All Java programs are composed of public static void main(String[] args) The method starts executing.

Java identifier

All components of Java require names. Class names, variable names, and method names are all called identifiers.

There are a few things to note about Java identifiers:

All identifiers should start with a letter (A-Z or a-z), dollar sign ($), or underscore (_)
The first character can be followed by any combination of letters (A-Z or a-z), dollar sign ($), underscore (_) or numbers.
Keywords cannot be used as identifiers
Identifiers are case sensitive
Examples of legal identifiers: age, $salary, _value, __1_value
Examples of illegal identifiers: 123abc, -salary

Java modifiers

Like other languages, Java can use modifiers to modify methods and properties in classes. There are two main types of modifiers:

Access control modifiers: default, public, protected, private
Non-access control modifiers: final, abstract, static, synchronized

We will discuss Java modifiers in depth in later chapters.

Java keywords

Java keywords are listed below. These reserved words cannot be used in the names of constants, variables, and any identifiers.

category	Keywords	illustrate
Access control	private	private
	protected	be protected
	public	public
	default	default
Class, method and variable modifiers	abstract	Declare abstraction
	class	kind
	extends	extend,inherit
	final	final value, immutable
	implements	Implementation (interface)
	interface	interface
	native	Native, native methods (non-Java implementation)
	new	new, create
	static	static
	strictfp	Strict and precise
	synchronized	thread, synchronization
	transient	short
	volatile	Volatile
program control statements	break	Break out of loop
	case	Define a value for switch to select
	continue	continue
	default	default
	do	run
	else	otherwise
	for	cycle
	if	if
	instanceof	Example
	return	return
	switch	Select execution based on value
	while	cycle
Error handling	assert	Assert whether an expression is true
	catch	catch exception
	finally	Execute regardless of exception
	throw	Throws an exception object
	throws	declares that an exception may be thrown
	try	catch exception
Package related	import	introduce
Package related	package	Bag
basic type	boolean	boolean
	byte	Byte type
	char	Character type
	double	double precision floating point
	float	single precision floating point
	int	integer
	long	long integer
	short	Short
variable reference	super	parent class, super class
	this	This category
	void	No return value
reserved keywords	goto	is a keyword, but cannot be used
	const	is a keyword, but cannot be used

Note:Java's null is not a keyword, similar to true and false. It is a literal constant and is not allowed to be used as an identifier.

Comment

//行注释
/*
块注释
可以多行一起注释
*/

Java empty line

Blank lines or lines with comments will be ignored by the Java compiler.

inherit

In Java, a class can be derived from other classes. If you are creating a class and there is already a class that has the properties or methods you need, then you can inherit the newly created class from that class.

Using inheritance, you can reuse methods and properties of existing classes without having to rewrite the code. The inherited class is called a super class, and the derived class is called a subclass.

interface

In Java, an interface can be understood as a protocol for objects to communicate with each other. Interfaces play a very important role in inheritance.

The interface only defines the methods to be used by the derived class, but the specific implementation of the method completely depends on the derived class.

The difference between Java source program and compiled execution

As shown below: