Getting the basics of Java variables

1, a variable
refers to a memory space in the computer memory, is the basic unit for storing data

Example:
Hotel - Memory
Hotel rooms each room contains the equivalent of a variable is
the room number - variable name
variable's data type - the type of room
guest room - variable values

2, the use of variable
declarations: variable name data type; for example: int money;
the assignment: variable name = value; for example:money=100;//将数值赋给money

3, declare variables
defined variables method:

1. First statement, then assignment: data type variable name; variable name = value;
2. Statement and assignment: data type variable name = value; // unassigned variables can not be used
3. A plurality of variable declaration and the same type of assignment: data type variable 1, variable 2, the value of the variable 3 = 3, 4 variable, the variable value 5 = 5;
   the PS: the Java is a strongly typed language, a variable type must match the type of the value

4, the data type of
the data type into basic data types and the reference data type

1. Basic data types: integer, decimal, character, Boolean
   ① integer
   
   byte (byte) 1Byte = 8bit Type 2 can store a total of 8 ^ 256 = an integer of 000 million to 127 plus 128 1111
   1111 128 128 -1 to negative number 1 represents a high negative zero positive sign bit byte data type of data indicated range: -128 to 127
   For type long, to be added later l or L

   ② decimal, floating-point
   
   decimal / float: using scientific notation
   2E3 equivalent to 2 10. 3 ^ = 2000.0;
   3E5 equivalent. 3 10. 5 ^ = 300000.0;
   Double float to the default type, To is float type assignment, the need to add F / f behind literal assigned For double type can be added D / d after the literal;

   ③ char
   char 2 bytes 0-65535 Unicode encoding (Unicode)
   the Unicode character set support ASCII code, wherein each character corresponds to a decimal integer;
   character assignment: char c1 = 'A';
   is an integer assignment: char c2 = 65;
   for the band assignment: char c3 = '\ u0041' ;
   escape character: \ n newline \ t indentation (tab stop) \ backslash 'single quotation marks "double quotes

   ④ boolean
   boolean 1 byte ture / false

2. Reference data types: string, array, objects, interfaces, classes
   string: String Any "" literal sequence of Unicode characters between the
   value of the method: String str1 = "hello";

5, conversion type
automatic type conversions: Two types compatible with each other and greater than the target type source type
byte-> SHORT-> INT-> Long
float-> Double
char can be converted to Short
char-> int
INT-> a float / Long
casts conversion: Two types compatible with each other and less than the target type source type

6, the expression

Use variables or literal operator connected, and a final result can be obtained.
Automatic lifting Type: two operands is a double, the calculation result is automatically elevated to Double; if not double, a float, the upgraded flaot; if not float, there is a long, to improve the Long; if the operation the number is not long, there is a int, then promoted to int; if not int, are short or byte, still promoted to int;

7, the operator

1. Arithmetic operator (two operands operation)
   + Add, summing
   - Save, difference
   * multiplication, quadrature
   / in addition, quotient
   % modulus, modulo
   ++ increments the value of the variable +1
   - decrements the value of the variable Save 1
   ++ / - to be used after the variable x, + 1 after the assignment operator (the first use, after +/- 1);

2. Assignment operator
   = direct assignment
   + = summed after the assignment
   - assignment after differencing =
   * = Quadrature after assignment
   / assignments = quotient after
   the assignment% = Remainder;

3. Relational operators
   greater than>
   Less than <
   greater than or equal to> =
   Less than or equal <=
   equal ==
   not equal! =

4. Logical operators
   && with (and) two data operands is true, the result is true;
   || or (or) has two operands is true, the result is true;
   ! NOT (negation) meaning "not" , true or false, false is truth;

5. Logical Operators shorting
   && with (and) short-circuited, when the left side of the expression is false, the right is not calculated, result is false;
   || or (or) or short-circuited, the left expression is true, the right is not calculated side, result is true;
   & with (and) a non-short-circuited, bitwise aND operator
   | or (or) the non-short circuit or, bitwise oR operator

6. Ternary operator
   first determines and then obtain corresponding results
   :? @ Semantics: boolean expression? Results 1: 2 results when the expression is true, the result obtained result; 2 results obtained;

7. Bitwise operators: two operands based on the calculated bit binary number

    &     位与    非短路与。两个数位，同时为1，结果为1
    |     位或    非短路或。两个数位，有一个为1，结果为1
    ^     异或     对应位上的数，相同为0，不同为1；
    ~     求反    按位求反1变0,0变1； 	
    >>	右移(带符号)    按位右移1位(高位补原符号位)；
    <<   左移    按位 左移1位；
   >>>  右移(无符号)    按位 右移1位(高位补0)；`
   

8, the console (keyboard) input

Program is running, the console may (terminal) manual data entry, let the program continues.

java.util.Scanner input = new java.util.Scanner(System.in);

Guide package syntax: import 包名.类名；// will introduce an external class file functionality into its own file
writing position: packageafter (if any), outside class, how can the sentence.
Each class has a defaultimport java.lang.*;

package *;
//引入Scanner包后
import java.util.Scanner;
//或者可以写为：import java.util.*;
public class * {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
	}
}

Order of use:
1, into java.util.Scanner;
two, a variable declared Scanner type Scanner sc = new Scanner(System.in);
3, using the Scanner function corresponding to the class (type distinction):
sc.nextInt();// get integer
sc.nextDouble();// obtained decimal
sc.next();//sc.nextLine (); obtaining the string
sc.next().charAt(0);// obtain a single the first letter of characters that the string