Java series (3)-basic syntax and java syntax
1. Keywords
Features: All lowercase letters
2. identifier
(1) It is the character sequence that names such as class, interface, and method.
(2) composition rules:
A: uppercase/lowercase letters
B: Number
C: $ and _
(3) considerations:
A: it cannot start with A number.
B: it cannot be a keyword in java.
C: Case Sensitive
(4) common naming rules
A: The packages are all in lower case and are separated by multi-level packages.
B: class or interface: uppercase letters of each word
C: method or variable: lowercase for the first letter, and uppercase for the second word
D: constant: all uppercase. Multiple words must be separated by _ (STUDENT_MAX_AGE)
3. Notes
(1) category:
A: When the line comment ://
B: multi-line comment :/**/
C: document notes:
(2) functions of Annotations:
A: Explain the program and improve the code reading.
B: It can help us debug the program.
4. Constants
(1) The value of the program remains unchanged during execution.
(2) category:
A: literal value constant
B: Custom Constants
(3) literal Constants
A: String constant
B: integer constant
C: decimal constant
D: character constant
E: Boolean constant
F: null constant, null
(4) java provides four representations for Integer constants
A: binary (starting with 0 B)
B: octal (starting with 0)
C: decimal (the default integer is decimal)
D: hexadecimal (starting with 0x)
5. hexadecimal conversion
(1) convert others to decimal
(2) convert decimal to other hexadecimal
(3) Fast Conversion Method of hexadecimal conversion
A: The conversion between decimal and binary. The code is 8421.
B: Binary and octal, hexadecimal conversion
6. Variables
(1) amount of changes that can occur within a certain range during Program Execution
(2) Definition Format of variables:
A: data type variable name = initialization value
B: data type variable name;
Variable name = initial value
7. Data Type
(1) java is a strong type language that provides a corresponding data type for each type of data
(2) category:
A: basic data types: 4 categories, 8 Types
B: Reference Data Type: Class, interface, array
(3) Basic Data Types
A: integer
[Byte: 1]
[Short: 2]
[Int: 4] [Default]
[Long: 8]
B: Floating Point Number
[Float: 4]
[Double: 8] [Default]
C: character
[Char: 2]
D: Boolean
[Boolean: 1]
8. Data Type Conversion
(1) The boolean type is not involved in conversion.
(2) Default conversion:
A: from small to big
B: byte, short, char → int → long → float → double
C: byte, short, and char are not converted to each other and are directly converted to the int type during calculation.
(3) forced conversion:
A: from big to small
B: It may cause loss of precision. It is generally not recommended.
C: Format: Target data type variable name = (target data type) (converted data)
[Example]