Scope of package class package

package

• Java Allow the use of packages （package） Organize classes .
• With the help of packages, you can easily organize your own code , And compare your own code with the code base provided by others Separate management .
• The standard Java Class libraries are distributed in multiple packages , Include java.lang、java.util、java.net etc.
• The standard Java Packages have a hierarchy , It's like a directory nesting on a hard disk , You can also use nested hierarchies to organize packages .
• All standard Java The bags are all in java and javax In the package hierarchy .
• Main of using package reason Is to ensure the uniqueness of the class name .
• Suppose two programmers have established Employee class , Just put these classes in different packages , There will be no Conflict .
• From the compiler's point of view , There is no relationship between nested packages .
• Such as ,java.util Bag and java.util.jar The bag has nothing to do with it .
• Each has a separate set of classes .

Class import

• A class can use all the classes in its package , And other public classes in the package （public class）.
• There are two ways to access public classes in another package .
  • Add the full package name before each class name , Such as java.time.LocalDate today = java.time.LocalDate.now();
  • A simpler and more common way is to use import sentence ,import A statement is a concise description that refers to a class contained in a package , Used import After statement , When using classes , You don't have to write the full name of the package .import java.util.*; LocalDate today = LocalDate.now();
• Only one package can be imported with an asterisk , Out of commission import java.* or import java.*.*; Import to java All packages for prefix .

Packet scope

• public Can be used by any class ;private Parts of can only be used by the classes that define them
• If not specified public or private, This part （ class 、 Method or variable ） Can be accessed by all methods in the same package