Java Basics-Variables and data types

Each language will be designed to a lot of data, so you will be exposed to different data types, the initial contact data type is also dizzy, Java language, finally a little understand, comb a bit, with June mutual encouragement.

• The concept of variables
  • A storage area in memory
  • Variable name + Data Type
  • Can be changed within the same type range

Why define variables:

Using variables Note:
• variable scope, one pair {}
• Initialize value

• definition The format of the variable:
  • data type    variable name = initialization value
  • eg:int x = 4
  • Note: Format fixed

• Understanding: Variables are like unknowns in mathematics.
• Data type :

the integer default type is :int

the decimal default type is :Double

Memory consumption and range of values

integral type	Occupy storage space (bytes)	size range
BYTE 	1	-128 ~ 127
short	2	-215 ~ 215 -1
int	4	-231 ~ 231 -1
long	8	-263   ~ 263 -1
floating-point	 	 
float	4	-3.403E38~ 3.403E38
double	8	-1.798E308~ 1.798E308
character type	 	 
char	2 ( adopted unicode encoding	 
Boolean type	 	 
boolean	1 ( 1/8byte)	 

parsing : Why byte takes one byte and the value range is -128~127

first you need to understand that in binary, the highest bit is the sign bit, 0 indicates positive, 1 represents a negative, and the other bits are data bits.

byte Total accounted 8 Bit , indicating the Number ( 2 8 ).

The maximum value is 01111111 , turn into decimal to 127

the minimum value is 10000000 , 1 is the sign bit, which represents a negative number, and turns it into decimal - . So The minimum value is -128 .

why exactly? -128 ? How are binary and decimal converted at the bottom? Will involve the original code, anti-code, complement , and listen to the next chapter analysis.

Summary:

In the final, the most important thing in software system is data, data is the core of the enterprise. Although some of the underlying things we do not need to be proficient, but only to understand these, later use can be handy, and then!

Java Basics-Variables and data types