Big Data <javase + Linux Elite Training class >_day_02

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1: Basic grammarvariable variables are small boxes in memory (small containers), what are containers?variables are loaded with data! 2: Basic grammarThe smallest unit of the computer's storage unit computer storage device"Bit" (bit), also known as "bit". The smallest storage unit of a computer is called"Bytes" (byte), B.    The bytes are made up of 8 bits. 1 bytes=8 bit 1B=8b 1024B=1KB1024 =1MB 1024MB=1GB 1024GB=1TB 1024TB=1PB3: Basic Grammardata Types in Java (four classes of eight) integer types-byteNumber of bytes: 1 Range: 128 ~ 127 ShortNumber of bytes: 2 range: 32768 ~ 32767intNumber of bytes: 4 range: 2147483648 ~ 2147482648LongNumber of bytes: 8Range: floating-point-floatNumber of bytes: 4single-precision floating point-DoubleNumber of bytes: 8double precision floating point precision high character type-CharNumber of bytes: 2 can represent a character, such as: ' A ' a ' ' ay 'Boolean type-BooleanNumber of bytes: 1 only two values:true        false4: Basic Grammarconstant and type integer constants can determine the type based on the scope in which the default integer type int type is in Java. Special:2147483641L, 100L is a long type. The floating-point type in Java is double by default, and"F".

5: Three elements of variable creation, base syntax

Partition: Specify the stored data type, and name
Create three elements of a variable: type, name, data

int a= 100;

6: Base Syntax--Define basic data type variables

Code block:

 Public  classvariable{ Public Static voidmain (String [] args) {//Defining integer Types        byteb = 127;                System.out.println (b);  Shorts = 32767;                        System.out.println (s); inti = 20001002;                System.out.println (i); //define a long type        LongL = 2147483649L;                System.out.println (l); //floating-point, single-precision float        floatf = 1.0f;                System.out.println (f); //floating-point, double-precision        DoubleD = 2.2;                System.out.println (d); //character        Charc = ' a ';                        System.out.println (c); //Boolean type True false        BooleanBoo =true;            System.out.println (Boo); }}

7: Basic syntax--Definition of string variable

 Public class variable_2{    /*         string with "" "Package," 0 ~    n "*     /Public staticvoid  main (String [] args) {        //  specifies data type    name    data, Represents the type of string        s = "I love Big Data development";        System.out.println (s);    }}

8: Considerations for variable definitions based on basic syntax

 public  class   variable_3{ /*              definition and use of variables 1, after the definition of the variable, do not assign a value, can not use 2, the definition of the valid range of variables, valid range within a pair of curly braces 3. Variables cannot be defined repeatedly  */ int  a = 1;  public  static  void   main (string[] args) { int
     i = 2;    System.out.println (i); }}

 9: Conversion of data types, base syntax-> auto convert  1: Range Small Data type value ( byte ), which can be converted directly to a large range of data type values (for example: int   2: Large range data Type value (int ), cannot be converted directly to a data type with a small range (for example: byte  ) Sort by data type:  byte ->short ->int -> Long ->float ->double -& gt; coercion type conversion 

 Public class variable_4{    publicstaticvoid  main (string[] args) {            //  defines a double type variable            double i =n;            System.out.println (i);    }}

 Public classdataconvert{ Public Static voidMain (string[] args) {DoubleD = 3.14; //int i = D; //System.out.println (i); //Forced ConversionsSystem.out.println ("=========== cast ================="); inti = (int) D;                System.out.println (i); byteB = (byte) 200;                System.out.println (b); System.out.println ("=========== and pick up ========"); System.out.println ("Chinese" + "country"); }}

10: Basic GrammarThe arithmetic operator computes the symbol for the data. Operator Arithmetic Rule Example results+ Plus +3 3 + + 4 + link character String "Chinese" + "country"China-Minus signNTA = 3;-a-3-minus 3-2 1 * multiplication 2*3                    6/Division Sign 5/2 2 modulo 5%2 1 + + self-incrementintA = 1;a++/++a 2--Self-reductionintb = 3;b--/--b 2 11: Basic syntaxassignment operator operator arithmetic rule results= assigned valueintA = 1; 2 + = Plus post-assignmentintA = 3;a+=2 4-= minus value assignmentintA = 2;a-=2 0 *= passenger after assignmentintA = 2;a*=2 4/= divisible AssignmentintA = 2;a/=2 1%= modulo assignmentintA = 2;a%=2 0

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Big Data <javase + Linux Elite Training class >_day_02