Basic data type and corresponding packing class

It seems that I haven't fully understood the difference between basic data types and packaging classes .

Basic data type

6 Number types ：byte、short、int、long、float、double
1 Types of characters ：char
1 Middle Boolean ：boolean

The corresponding packaging class Byte、Short、Integer、Long、Float、Double、Character、Boolean

Number of digits of basic type 、 byte 、 The default value is

Java Use in long The type of data must be followed by the number L, Otherwise, it will be parsed as an integer .
Java Use in long The type of data must be followed by the number L, Otherwise, it will be parsed as an integer .

Packing

Wrap basic types with their corresponding reference types .

Unpacking

Convert wrapper type to base data type .

For example, use Integer Three objects are created abc,a=b+c, because + Cannot be used in Integer Inter object operation , It will unpack automatically .

Wrapper classes and constant pools

Java Most of the basic types of wrapper classes implement constant pool technology , namely Byte, Short, Integer, Long,Character,Boolean.Byte,Short,Integer,Long The default value is created [-128,127] The corresponding type of cached data ,Character Created values in [0,127] Range cache data ,Boolean Go straight back to True Or False. If it goes beyond the corresponding range, it will still create new objects .

Two types of floating-point wrapper classes Float,Double Constant pool technology is not implemented .

Integer i1=40//Java  When compiling, it will directly encapsulate the code as  Integer i1=Integer.valueOf(40);, To use the objects in the constant pool .
Integer i2 = new Integer(40)// In this case, a new object is created .
System.out.println(i1==i2)// Output  false