Java - Basci Data Type 基本数据类型

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");