变量----存储数据的容器
两种数据类型
- 原始数据类型
- 引用数据类型
原始数据类型
Java支持8种原始数据类型，原始数据类型都是被预定义的，并附带关键词命名
- byte
- 字节类型是一个8位有符号二的补码整数
- 最小值是-128 （-2的7次方）
- 最大值127 （2的7次方-1）
- 默认值0
- 字节数据类型用于节省大型数组中的空间，主要用于代替整数，因为字节比整数小四倍。
- short
- int
- long
- float
- double
- boolean
- char
short
Short data type is a 16-bit signed two's complement integer
Minimum value is -32,768 (-2^15)
Maximum value is 32,767 (inclusive) (2^15 -1)
Short data type can also be used to save memory as byte data type. A short is 2 times smaller than an integer
Default value is 0.
Example: short s = 10000, short r = -20000
int
Int data type is a 32-bit signed two's complement integer.
Minimum value is - 2,147,483,648 (-2^31)
Maximum value is 2,147,483,647(inclusive) (2^31 -1)
Integer is generally used as the default data type for integral values unless there is a concern about memory.
The default value is 0
Example: int a = 100000, int b = -200000
long
Long data type is a 64-bit signed two's complement integer
Minimum value is -9,223,372,036,854,775,808(-2^63)
Maximum value is 9,223,372,036,854,775,807 (inclusive)(2^63 -1)
This type is used when a wider range than int is needed
Default value is 0L
Example: long a = 100000L, long b = -200000L
float
Float data type is a single-precision 32-bit IEEE 754 floating point
Float is mainly used to save memory in large arrays of floating point numbers
Default value is 0.0f
Float data type is never used for precise values such as currency
Example: float f1 = 234.5f
double
double data type is a double-precision 64-bit IEEE 754 floating point
This data type is generally used as the default data type for decimal values, generally the default choice
Double data type should never be used for precise values such as currency
Default value is 0.0d
Example: double d1 = 123.4
boolean
boolean data type represents one bit of information
There are only two possible values: true and false
This data type is used for simple flags that track true/false conditions
Default value is false
Example: boolean one = true
char
char data type is a single 16-bit Unicode character
Minimum value is 'u0000' (or 0)
Maximum value is 'uffff' (or 65,535 inclusive)
Char data type is used to store any character
Example: char letterA = 'A'
引用数据类型