JAVA-based keywords, reserved words and identifiers

Keywords:

1. The definition and characteristics of keywords

1. Definition: A string (word) given a special meaning by the Java language and used for special purposes
2. Features: All letters in the keywords are lowercase
3. Official address:
   https://docs.oracle.com/javase/tutorial/java/nutsandbolts/_keywords.html

Keywords used to define data types
class	interface	enum	byte	short
int	long	float	double	char
boolean	void
Keywords used to define process control
if	else	switch	case	default
while	do	for	break	continue
return
Keywords used to define access permission modifiers
private	protected	public
Keywords used to define class, function, variable modifiers
abstract	final	static	synchronized
Keywords used to define the relationship between classes
extends	implements
Used to define the keywords for establishing and referencing instances and judging instances
new	this	super	instanceof
Keywords for exception handling
try	catch	finally	throw	throws
Keywords used for packages
package	import
Other modifier keywords
native	strictfp	transient	volatile	assert
* Used to define the literal value of the data type value
true	false	null

2. Reserved word (reserved word)

• Java reserved words: the current Java version has not been used, but future versions may be used as keywords. Avoid using these reserved words when naming identifiers yourself.
• goto 、const.

3.Identifier

Identifier:

• The character sequence that Java uses when naming various variables, methods, and classes is called an identifier.
• Tip: Any place where you can name it is called an identifier.

Define legal identifier rules:

• It consists of 26 uppercase and lowercase letters of English letters, 0-9, _ or $
• Numbers cannot start.
• Keywords and reserved words cannot be used, but keywords and reserved words can be included.
• Java is strictly case-sensitive, and the length is unlimited.
• The identifier cannot contain spaces.

Naming conventions in Java:

• Package name: All letters are lowercase when multiple words are formed: xxxyyyzzz

• Class name, interface name: when multiple words are formed, the first letter of all words is capitalized: XxxYyyZzz

• Variable name and method name: When multiple words are formed, the first letter of the first word is lowercase, and the second word starts with uppercase of each word: xxxYyyZzz

• Constant name: All letters are capitalized. When there are multiple words, each word is connected with an underscore: XXX_YYY_ZZZ

• Note 1: When naming, in order to improve readability, it should be as meaningful as possible, "see the name to know the meaning".

• Note 2: Java uses unicode character set, so the identifier can also be declared in Chinese characters, but it is not recommended.

Next chapter: Variables based on JAVA (data types and conversion)