Identifier:
JAVA sequence of characters used for a variety of variables, methods and the like named elements become identifier.
Tip: Those who own place from the name of the call identifier.
Define the legal rules for identifiers:
1. The case of the 26 English letters, 0-9, or _ $ Composition
2. The numbers can not begin with.
3. Keywords and reserved words can not be used, but can contain keywords and reserved words
4.Java strictly case-sensitive, unlimited length.
The identifier can not contain spaces.
示例：miles,Test,a++,--a,4#R,$4,#44,apps,class,public,int,x,y,radius
Naming conventions:
Package name: multi-word when all letters are lowercase: xxxyyyzzz
Class name, interface name: multi-word, the first letter of all words capitalized: XxxYyyZzz
Variable names, method names: multi-word, lowercase first letter of the first word, the second word began to capitalize the first letter of each word: xxxYyyZzz
Constant name: All the letters are capitalized. When many words each word with an underscore: XXX_YYY_ZZZ
Note 1: When a name, in order to improve readability, to try to make sense, "see the name to know Italian."
Note 2: java using unicode character set, so the identifier can also use Chinese characters declaration, but not recommended.
