基本数据类型
variable，其实什么也不是，只是通过内存位置来保存值。这就意味着你创建变量的时候，也在内存里保留里空间。
基于变量的数据类型，操作系统分配内存，并且决定什么可以储存在保留内存中。因此，通过分配不同数据类型的变量，可以被赋值 整数、小数、字符等在变量里。
Java里有两大类数据类型：
- Primitive Data Type 原始数据类型
- Reference / Object Data type 引用数据类型
Primitive Data Type
八种基本类型：
byte
Byte data type is an 8-bit signed two's complement integer
Minimum value is -128 (-2^7)
Maximum value is 127 (inclusive)(2^7 -1)
Default value is 0
Byte data type is used to save space in large arrays, mainly in place of integers, since a byte is four times smaller than an integer.
Example: byte a = 100, byte b = -50
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'
Reference DataTypes 引用数据类型
引用变量是使用定义的构造函数的类创建的。它们是用于访问对象。这些变量声明为特定类型的不能被改变。例如,雇员,小狗等
Example: Animal animal = new Animal("giraffe");
