inner class typical example

1. A class defined within another class is called an inner class.

2. Inner classes are distinctly different from composition. (inner classes > composition)

// innerclasses/Parcel2.java
// (c)2017 MindView LLC: see Copyright.txt
// We make no guarantees that this code is fit for any purpose.
// Visit http://OnJava8.com for more book information.
// Returning a reference to an inner class

public class Parcel2 {
  class Contents {
    private int i = 11;

    public int value() {
      return i;
    }
  }

  class Destination {
    private String label;

    Destination(String whereTo) {
      label = whereTo;
    }

    String readLabel() {
      return label;
    }
  }

  public Destination to(String s) { // returns a reference to an inner class Destination
    return new Destination(s);
  }

  public Contents contents() { // returns a reference to an inner class Contents
    return new Contents();
  }

  public void ship(String dest) {
    Contents c = contents();
    Destination d = to(dest);
    System.out.println(d.readLabel());
  }

  public static void main(String[] args) {
    Parcel2 p = new Parcel2();
    p.ship("Tasmania");
    Parcel2 q = new Parcel2();
    // Defining references to inner classes:
    Parcel2.Contents c = q.contents(); // note this
    Parcel2.Destination d = q.to("Borneo");
  }
}
/* Output:
Tasmania
*/

references:

1. On Java 8 - Bruce Eckel

2. https://github.com/wangbingfeng/OnJava8-Examples/blob/master/innerclasses/Parcel2.java