Java Chapter II: Data Types and operators

Today just class, Yang teacher said the conversion between the system: 16 binary: 1,2,3,4,5,6,7,8,9,a,b,c,d,e,f. Already mastered, just a stroke!

decimal integers, such as: 99,-500, 0
octal integers, which require starting with 0, such as: 0 15
Hexadecimal number, requires 0x or 0X, such as: 0x 15

Java is a strongly typed language with a naming convention for identifiers:

Can only be a letter, _, number, $ composition, and the first digit cannot be a number! Can not use keywords, strict case-sensitive, hump naming method, do see the name of the idea!

Data types in Java:

Basic data types: 4 Class 8, Integer type: Byte (1 bytes), short (2 bytes), int (4 bytes), Long (8 bytes), Float type: float (single precision, 4 bytes), double (doubles, 8 bytes), Character: char (2 bytes), Boolean: Boolean (1-bit/1bit, can only be ture or false). 1 bytes/1byte=8bit/8 bits.

Reference data type: Class, Interface (interface), array.

Unicode encoding set is International, 2 bytes, can represent a Chinese character (two bytes); 1 The default is the int type. 3.14 The default is the Doublie type . float pi = 3.14F This is the right way to write!

The final modified variable is constant, cannot be re-assigned, and the variable is best capitalized pi.

Scanner input = new Scanner (system.in);//Get the input stream of the keyboard, need the guide package before use: Import Java.util.Scanner;

Class Name Object name = new class name (parameter);//How to create an object

The assignment operator and the three-mesh operator have the lowest precedence, () [] have the highest precedence.

Data transformations in Java
1. Automatic conversion: Two data types are compatible with each other, the target type is greater than the source type (the range of small to large automatic conversion).
BYTE--->short-->int--->long--->float--->double
If multiple data types are mixed, the result should be the type with the largest range
2. Cast: The loss of precision can occur, even data distortion.
Syntax: (data type) an expression or variable;
Eg:double f=3.14;
int i = (int) F;

　　

Java Chapter II: Data Types and operators