02-05 Java language basics (variables, data types)

Variable overview

• What is a variable?
  The amount by which the value can change within a certain range during program execution

• Variable definition format
  Data type variable name = variable value

• Why define variables
  to store constants of the same type continuously, and can be reused

type of data

• Why have data types? The
  Java language is a strongly typed language. For each type of data, a clear specific data type is defined, and different sizes of memory space are allocated in the memory.

• Classification of data types in Java
  Basic data types
  Reference data types

• Basic data type
  integer

  Keyword	size	range
  byte	One byte	-128~127
  short	Two bytes	-2^15 ~ 2^15 - 1
  int	Four bytes	-2^31 ~ 2^31 - 1
  long	Eight bytes	-2^63 ~ 2^63 - 1

  Floating point

  Keyword	size	range
  float	Four bytes	-3.403E38 ~ 3.408E38
  double	Eight bytes	-1.798E308 ~ 1.798E308

  Character type

  Keyword	size	range
  char	Two bytes	0~65535

  Boolean

  Keyword	size	range
  boolean	No clear size	true、false