Java Fundamentals 2-Basic syntax

1. Identifier: A sequence of characters used to name a class, interface, method, variable, etc.

Composition rules: English uppercase and lowercase letters, numeric characters, $ and _
Note: Cannot start with a number, cannot be a keyword in Java, is case-sensitive

2. Note: The text used to interpret the description program.
Note Classification format in Java: (1) Single-line Comment://(2) Multiline Comment:/* can't see Me */(3) document Comment:/** can't see me * *

3. Constant: Its value cannot be changed during program execution.

Constant classification: Literal constants, custom constants

Literal constants (1) string Constants "Hello" (2) Integer Constants 12,23 (3) Decimal Constants 12.34 (4) Character constants ' A ', ' a ', ' 0 ' (5) Boolean constant True,false (6) NULL constant NULL
4. Variable: The amount of the value that can change within a certain range during the execution of a program.

Variable definition Format: (1): Data type variable name = initialization value, (2): Data type variable name; Variable name = initialization value;

5. Data type and type conversion

(1) Java is a strongly typed language that provides the corresponding data types for each type of data.
(2) Category: A: Basic Data Type: 4 Class 8 kinds B: Reference data type: Class, interface, array.
(3) Basic data types
A: Integer occupies bytes byte 1 short 2 int 4 long 8 B: Floating-point number float 4 Double 8
C: Char 2 D: Boolean Boolean 1
Note: integers By default are of type int, and floating-point numbers are double by default.   Long integers to be added L or L. Single-precision floating-point numbers are added F or f.

6: Data type conversion
(1) Boolean type does not participate in conversions
(2) Default conversion
A: From small to large
B:byte,short,char--INT--long--float--double
C:byte,short,char do not convert each other, directly into the int type participates in the operation.
(3) Forced conversion
A: from big to small
B: There may be a loss of precision, generally not recommended for such use.
C: Format:
Target data type variable name = (target data type) (converted data);

7. Operators

Precedence of operators (high-to-low)

Priority level	Describe	Operator
1	Brackets	(),[]
2	PLUS sign	+,-
3	auto-subtract, non	++ , --, !
4	multiplication, taking surplus	*,/,%
5	Add and Subtract	+,-
6	shift operation	<< , >> , >>>
7	size relationship	> , >= , < , <=
8	Equality relationship	= =,!=
9	Bitwise-AND	&
10	Bitwise XOR OR	^
11	Bitwise OR	|
12	Logic and	&&
13	Logical OR	||
14	conditional operations
15	Assignment operation	= , += , -= , *= , /= , %=
16	Bit assignment operations	&=,|=,<<=,>>=,>>>=

8. Keywords

Abstrac indicates that a class or member method has an abstract property	Assert assertion, which is used for program debugging	One of the Boolean basic data types, Boolean type	Break jumps out of a block early	One of the byte base data types, byte type
Case is used in a switch statement to indicate one of the branches	Catch is used in exception handling to catch exceptions	Char one of the basic data types, character type	Class declares a category	Const Reserved keywords, no specific meaning
Continue Back to the beginning of a block	Default Default, for example, used in a switch statement , indicates a default branch	Do Used in the DO-WHILE loop structure	Double One of the basic data types, double-precision floating-point number types	Else Used in a conditional statement to indicate a branch when the condition is not true
Enum Enumeration	Extends Indicates that one type is another type of subtypes, where common types have classes and interfaces	Final Used to describe the final attribute, indicating that a class cannot A subclass is derived, or the member method cannot be overwritten The value of the member domain cannot be changed, Used to define constants	Finally Used to handle exception cases, to declare a block of statements that are essentially bound to be executed	Float One of the basic data types, single-precision floating-point number types
For A guide word for a cyclic structure	Goto Reserved keywords, no specific meaning	If Guide Words for conditional statements	Implements Indicates that a class implements the given interface	Import Indicates that you want to access the specified class or package
instanceof Used to test whether an object is an instance object of the specified type	Int One of the basic data types, integer type	Interface Interface	Long One of the basic data types, long integer type	Native Used to declare a method that is implemented by a computer-related language (such as the C/c++/fortran language)
New Used to create a new instance object	Package Package	Private An access control method: Private mode	Protected An access control method: Protection mode	Public An access control method: Common mode
Return Returning data from member methods	Strictfp Used to declare fp_strict (single-precision or double-precision floating-point numbers) Expression follows IEEE 754 arithmetic specification	Short One of the basic data types, the short integer type	Static Indicates a static property	Super Indicates a reference to the parent type of the current object or a constructor for the parent type
Switch Guide words for Branching statement structures	Synchronized Indicates that a piece of code needs to be executed synchronously	This Reference to the current instance object	Throw Throws an exception	Throws Declares all exceptions that need to be thrown in the currently defined member method
Transient Declaring a member domain without serialization	Try Try a block that might throw an exception	void Declares that the current member method does not return a value	Volatile Indicates that two or more variables must be changed in a synchronized manner	While Used in the loop structure

　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　

Author: luvsangiin Source: http://www.cnblogs.com/eeddee/p/8721871.html

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Java Fundamentals 2-Basic syntax