Wow, it's so rich.

It's in 2022 One morning in, Zhuge thirteen met two people ： Zhang San and Zhang Sanfeng .

Yes , Zhang San is the outlaw maniac , Zhang Sanfeng is the old man with a long beard .

Someone asked , What's the relationship between them , As you can see , They are both human beings , And the name contains Zhang San , That's it .

Many people ask Java Follow JavaScript What does it matter , They are both a programming language , And the name contains Java, That's it .

JavaScript It's a weakly typed language , No matter how it is used var、const still let Can store any type of data .

Java Is a strong type of language , Each variable must specify a type （ as for JDK10 Supported by var Modify local variables , Let's talk about it , What I'm talking about now is JDK8）

Many friends who have just graduated will be asked in the interview ：Java There are several basic data types ？ What are they ？ What are their characteristics ？ How many bytes ？

Ask someone who has just graduated this question , Mainly to investigate his basic skills .

Let's have a brief talk next Java The base type

One 、Java There are several basic types

Java Yes 8 Basic data types , Respectively ：

• 6 Number types ：
  Integer type ： byte、short、int、long
  floating-point ：float、double
• 1 Types of characters ：char
• 1 Middle boolean type ：boolean

Two 、 Briefly introduce this 8 Type of data

2.1 byte

• byte The data type is 8 position 、 The signed , An integer represented by a binary complement （ The computer indicates that the complement is used , As for why , And what is the original code 、 Inverse code 、 Complement code , This is the knowledge of College , Forget the , Wait for me , The next one is about ）

• minimum value -128 （-2^7）

• Maximum 127 （2^7 -1）

• The default value is 0

• Example ： byte b = 10, byte by = -2;

• byte Type is used in large arrays to save space , Of course, mainly with int To compare ,int Occupy 4 Bytes , One value is byte Of 4 times , But we must pay attention to the scope , If the value range is not byte Within the maximum and minimum range , Let's not use byte According to the .

• How to calculate the maximum and minimum , We will also write this separately in the next article , Actually short、int、long similar

2.2 short

• short The data type is 16 position 、 A signed integer represented by a binary complement
• The minimum is -32768 （-2^15）
• The maximum is 32767 （2^15 -1 ）
• The default value is 0
• Example ：short s = 1888, short sh = - 1999;
• short Data types can also follow byte Save space as well , One short The space occupied is 2 individual byte size , But it's half int size

2.3 int

• int The data type is 32 position 、 A signed integer represented by a binary complement
• The minimum is -2147483648 （-2^31）
• The maximum is 2147483647 （2^31 -1 ）
• The default value is 0
• We usually write code , It's all direct use int type , Because now computer memory is not a big problem , We mainly focus on the realization of functions , But we need to know byte、short、int The amount of memory occupied by , And data range , no need , But you don't have to know .

2.4 long

• long The data type is 64 position 、 A signed integer represented by a binary complement
• The minimum is - 9223 372 036 854 775 808 （-2^63）
• The maximum is 9223 372 036 854 775 807 （2^63 -1 ）
• The default value is 0L
• Be careful ： We'll use it again long Type data must be added after the value L( Case insensitive , But it's better to use capital letters , A lowercase letter “l” And figures “1” Easily misread )
• Example ： long a = 19234034L, long b = -123243434L;
• We use... In our program long type , Generally, it means time stamp 、 Self increasing id、 amount of money （ The amount does not need to be fload、double stay Java We usually use long Store points or use Bigdecimal Storage element ）

2.5 float

• float The data type is single precision 、32 position 、 accord with IEEE 754 Standard floating point numbers （ What is? IEEE 754 standard , And why fload、double Cannot represent an exact value , For example, currency , We will also talk about in the following article ）
• fload Memory can be saved when storing large floating-point arrays （ And double Compared to just ）
• The default value is ： 0.0f
• Example ： fload f = 232.3f; To add f

2.6 double

• double The data type is double precision 、64 position 、 accord with IEEE 754 Standard floating point numbers
• The default type of floating-point number is double type , That's why we define float You need to add f
• double And float equally , Cannot represent an exact value
• The default value is \u0000 Empty space
• Example ：double d = 23.1,double d2 = -23343.3434;

2.7 char

• char The type is a single 16 Bit unicode character
• minimum value \u0000 It's empty To an integer, that is 0
• Maximum \uffff To an integer, that is 65535
• char The data type can store any character
• Example ： char e = ‘B’,char r =‘ Love ’ Attention WOW , Here is the single quotation mark , Rarely in Java I see single quotation marks in

2.8 boolean

• boolean Information representing a person

• Only two values ： true false

• The default value is ： false

• Example ： boolean flag= true;

• boolean How much space does the type take up Logically speaking, it means true or false 0 and 1 One bit It means
  however Java The virtual machine specification says ： Use alone boolean After compilation, it will be converted to int Type is 4 Bytes , If it is boolean Array words , After compilation, it will be converted to byte Type is 1 Bytes . This depends on the specific virtual machine implementation , Whether it is according to the specification .

There are many new entrants. Look at these types , This is also a must for entry ,