Java Basics (two) variables and data types
Review:
1. What is the programming
2.Java programming language and its history
Step 3. Use Notepad to develop Java programs
4. The package name rules
In this chapter:
1.why the What??
2. Variable three elements
3. Master variables and constants
And finally the difference between 4.final and finalize the
The master data type conversion
1.why? What?
RAM: run-time memory when you power off the computer, shut down, data will be lost or crashes
ROM: Read Only Memory, C drive, D drive
To store the variable data, represented by a character instead of a number or string, to modify and maintain the code
Variables: To store data, the address is not convenient to use when the program runs, it leads to a variable name.
2. The three elements of variable
data types
① The first classification
Value Type
Integer: int (default integer)
Floating-point (decimal): double (double precision by default), float
Non-numeric types
String (String): as long as the double quotation marks are strings. "Name"
character (char): sheets quotation marks is the character 'M' 'female' 'A'
** boolean (boolean): true true / false false **
② The second classification
The basic data types: very common, are the key color in the IDE int double char boolean ...
reference data types: arrays, classes (String data type is a reference), the interface ...
the variable name (important)
Rules:
① see the name EENOW
② variable names consist of letters, numbers, underscores as well as the $ sign, but the number can not start, can not appear keywords.
Keywords: system defines the special meaning of the word (in the IDE the color has changed)
, for example: public static int class ...
③ method using camelCasing
Example: storing user information wodemingzi -> nomenclature employed hump -> woDeMingZi
-> using the underscore splicing -> wo_de_ming_zi
hump nomenclature :( small hump nomenclature)
first letter lowercase, if there is more than one word, the first letter of each word capitalized behind.
myUserInfo
PS: class name (Pascal nomenclature / big hump nomenclature)
first letter of each word is capitalized! HelloWorld
<font size = 4> ** ④ English either all, or pinyin, must not mashup ** </ font>
. 1
variable value
3. Variables and Constants using
variable set → → → Array XML → → non-relational database relational database → → large data cache
Variables used:
1. declare variables: the data type of a variable value divided memory space int num
2. assign values to variables: a stored value to this variable space num = 10
3. Variable ... variable value obtained according to the variable name can be used as the arithmetic output can also be used
Variable name assignment Data type 4 = variable value of variable declaration while int num = 10
constant
The program is running, there are some data did not want it to be re-assigned, can be modified with final
final double Pi = 3.1415926927
Constant naming convention:
1. All the letters are capitalized words
2. If there is more than one word, using the connections between the plurality of words _
3.MENU_PAGE_CONTEXT
Interview questions:
And finally the difference between final and finalize the
4. The master data type to
1. Type integer ranging from small to large: byte → short → int → long → float → double
2. Low → High accuracy (automated implicit type conversion)
3. High → low accuracy (casts, loses precision)
Interview questions
++ and -