导入Java类运行时和编译

Question

Could someone explain what importing java.net.* imports? Also could someone explain briefly how importing say java.swing.* would affect the run-time and compilation.

Answer 1

Importing a package, class, or any class member simply makes it possible to use that component's Simple Name instead of needing to use its Fully Qualified name. It doesn't affect runtime. It is a compilation feature. So instead of having to write

java.net.URL url = ...

you could simply write

URL url = ...

it won't affect performance or anything like that.

Answer 2

java.net.* will import all classes of the java.net package. java.swing.* should have little affect on run-time and compilation because it is written entirely in Java and follows standard class hierarchy rules.