packages and imports

A way of organising interfaces and classes, to avoid conflicts. Similar to directories. Logically group similar items together. Applying access restriciton to the package.

Package names are in lowercase and cannot start with special character or digit. Can have _ in the name.

Any class in a package can access anything in other classes that is not private defined

• static imports

import static java.lang.System.out;

out.println("Hello static  import!");

import static <package>.ImportsExamples.SOME_CONSTANT;

String constant = SOME_CONSTANT;
// Instead of String constant = ImportsExamples.SOME_CONSTANT;

• import one

  import com.hanfak.Dog;

• import all

  import com.hanfak.*;

  • Imports all classes from this package

  • not good if only need to import up to 2 or 3 classes

• Same class conflicts

  • Use fully qualified name

  com.hanfak.Dog.run();
  
  com.hanfak.Dog dog = new com.hanfak.Dog();

  • When another import has same Class name and thus conflict

• class path

  • libraries/classes that accessible

Advantages

• define their own packages to bundle a group of classes/interfaces

• package creates a new namespace there won't be any name conflicts with names in other packages

  • removes naming collision

• it is easier to provide access control

• easier to locate the related classes.

• Understand the structure of the app, screaming architecture