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Analysis of Java SE 030 Package and Import Statement
Article Directory
1. Package
(1) It is used to classify the categories that complete different functions and place them in different directories (packages).
(2) The package naming rule, the company domain name is reversed as the package name.
The domain name is unique on the Internet, and the package is the same. In a project, the package name is also unique. It is impossible for two packages with the same name to exist.
(3) For the package name: each letter needs to be lowercase.
(4) If the package is not used when defining, then Java thinks that the class we define is in the default package.
2. Compile java source files with package declaration
There are two forms:
(1) Compile directly, and then put the generated class file in the directory structure (rarely used, more troublesome).
(2) Use the compilation parameter -d, the method is javac -d ./c:/directory name source file.java, so that after compilation, the compiler will automatically help us establish the directory structure corresponding to the package.
There are two packages, namely aa.bb.cc and aa.bb.cc.dd, then we call the latter a sub-package of the former.
3. Import (import)
(1) Import back each class separated by package, so that the compiler can find the required class.
Commentary:
Import is an imported class, that is, you need to write the package name and class name in full after import.
grammar:
（1）import com.test.ImportTest;
（2）import com.test.*;表示导入com.test包下面所有的类。
注意：import aa.bb.*并不会导入aa.bb.cc包下面的类。这时需要这样写：
import aa.bb.*;
import aa.bb.cc.*;
（3）注意：如果两个类在同一个包下面，那么则不需要导入，直接使用即可。
4. About the order of package, import, and class
(1) First, you need to define a package, which is optional.
(2) Use import to import, optional.
(3) Define class or interface. Package, optional.
(4) Use import to import, optional.
(5) Define class or interface.