Overview of common classes

java.lang package ：Java The core package of language , All contents of this package are Java The virtual machine is automatically imported , Such as System class 、String class

java.util：Java Language toolkit , Such as Scanner class 、Random class 、List aggregate ;

java.sql： Data packets , Contains a large number of classes and interfaces for operating the database ;

java.io： I / O package , Such as FileInputStream class 、FileOutputStream class ;

java.net： Network package , Contains classes related to network programming , Such as ServerSocket class 、Socket class ;

Object class ：java.lang.Object Class is the parent of all classes ; The methods include equals()、hashCode()、toString();

Packaging ： Make variables of basic data types into classes ; Common methods ：xxxvalue(), Get... In the calling object xxx Type data , That is, unpacking ;valueOf(xxx x), according to x Get the object of the corresponding wrapper class , I.e. packing ;Java5 After that, the function of automatic disassembly and assembly of the box was added ;parseXxx(String s), String to basic data type ;

java.lang.Math Class is used to provide methods for performing mathematical operations ;

java.math.BigDecimal Class can perform exact operations ;

java.math.BigInteger Class can represent more than long Integer data with large type range ;