Identifier

• Some names that are customized in the program.

• Composed of 26 English letters, number: 0-9 Symbol: _ $

• Define legal identifier rules:1. The number cannot be started.

2. No keywords can be used.

• Java is strictly case sensitive.
• Note: When making a name, try to make sense as much as possible to improve your reading.

2. Name specification

Name specification in Java:

• Package Name: All letters are lowercase when composed of multiple words.

       • xxxyyyzzz

• Class name interface name: When multiple words are composed, the first letter of all words is capitalized.

       • XxxYyyZzz

• Variable name and function name: When multiple words are composed, the first word is lowercase and the second word begins with the first letter of each word.

       • xxxYyyZzz

• Constant name: All letters are capitalized. Each word is connected with an underscore when multiple words are used.
  • XXX_YYY_ZZZ

3. Data type

Among them, the basic data type size is as follows:

Integer type: (The bold part below is the wrapper class for each data type)
byte (1 byte) (Byte), short (2 bytes) (Short), int (4 bytes) (Integer), long (8 bytes) (Long)
Floating point type:
float(4 bytes)(Float), double(8 bytes)(Double)
Logical:
boolean(true/false)(Boolean)
Character:
char (2 bytes) (Character)

Byte: A byte type integer occupies 8 bits in memory. The range of the table number is -128(-2^7)~127(2^7-1)
short: A short type integer takes up 16 bits in memory, and the table number ranges from -32768(-2^15)~32767(2^15-1)
int: An integer of type int occupies 32 bits in memory, and the range of the table number is -2147483648(-2^31)~2147483647(2^31-1)
long: A long type integer takes 64 bits in memory, and the table number ranges: (-2^63)~(2 ^63-1)

Note: long l = 4l;

       float f = 2.3f; 

The range of the basic data type is byte->short->int->long->float->double (range from small to large)

Basic data type interview questions:

[java interview questions] Basic data types and other issues: