Regain Java Memoirs (i): JAVA01 basic data types and basic statements

Basic requirements for writing Java programs

1. Writing Java classes is actually writing Java files ( By default, the class name and file name require the same )

2. When writing a class, it should be placed in a package

meaning of the package : display of a folder ( reflection of the hierarchical relationship of a document )

The hierarchy in the package depends. Layer in to differentiate between different Java files

The application between packages

1. Create the class package name (indicating the location of the class)

2. Use the class import package name. class name (can use * to represent all)

Basic data type:

1. Identifiers

Named rules:

1. Letters, underscores, numbers, $, composition, but numbers cannot be started

2. Case sensitive

3. Cannot use keywords

4. Habits

1. Requires a certain semantics, all the letters lowercase

2. The first letter of the class name is capitalized student, and the first letter of the variable name is lowercase studentname

3. Connect File_path between words

2. Basic data type (8 types)

1. Integral type

Byte	1 b 8 bit	-128--127
short	2b                    16	-2^15	 	Span style= "font-size:18px" > 	 
int	4                      32	-2^31	 		 
Long	8 64	-2^63

2. Floating point

Float	4 B 32
Double	8B 64

3. Characters

Char	2 16
4. Boolean
Boolean	1 b True/false

Conversions between types

1. The positive

Byte-short (char)-int-long-float-double

2. Reverse (forced conversion)

(conversion type) identifier/number

Features of Java

Reference data type

Class, interface, array

Reference type identifier (variable) = new reference type (parameter)/[parameter]: constructor of reference type

String S=new string ("");

Int arr[] =new int[10]

Difference between reference type and base type ( memory )

Stack memory: Storing simple data types (variable names and values)

Heap memory: Used in conjunction with stack memory, where the first address of the heap memory is stored, and the referenced instance is stored in the heap (the portal/attribute of the definition of the method)

Basic statement:

Operator

Shift Operators

>> All symbols Right shift

>>> right-shift high-fill 0

logical operators

&/|

&&/| |

!

Arithmetic operations

+ + use: do not use i+=1;

Declaration of a process statement variable

Global variables: Scope is the entire file

Local variables: part of the method

Use of Operators

Order

Branch if: else/

Switch (Byte/short/int/char)

...

Cyclic for/while

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Reference type

Array: is an object

Declaring an array

type [] array; Recommended /Type array[]

Create an array

Space in the heap memory, specifying the length of the array, length once specified cannot be changed

Multidimensional arrays

Type []: array//Declaration and creation

Properties and methods of arrays

Arrays are provided by JAVAAPI, with certain methods and properties

Regain Java Memoirs (i): JAVA01 basic data types and basic statements