Choosing composition vs. inheritance

Bruce Eckel's Thinking in Java Contents | Prev | Next

vs. inheritance

//: Car.java
// Composition with public objects
 
class Engine {
  public void start() {}
  public void rev() {}
  public void stop() {}
}
 
class Wheel {
  public void inflate(int psi) {}
}
 
class Window {
  public void rollup() {}
  public void rolldown() {}
}
 
class Door {
  public Window window = new Window();
  public void open() {}
  public void close() {}
}
 
public class Car {
  public Engine engine = new Engine();
  public Wheel[] wheel = new Wheel[4];
  public Door left = new Door(),
       right = new Door(); // 2-door
  Car() {
    for(int i = 0; i < 4; i++)
      wheel[i] = new Wheel();
  }
  public static void main(String[] args) {
    Car car = new Car();
    car.left.window.rollup();
    car.wheel[0].inflate(72);
  }
} ///:~ 

Because the composition of a car is part of the analysis of the problem (and not simply part of the underlying design), making the members public assists the client programmer’s understanding of how to use the class and requires less code complexity for the creator of the class.



Comments

  • There are no comments yet. Be the first to comment!

Leave a Comment
  • Your email address will not be published. All fields are required.

Top White Papers and Webcasts

  • With JRebel, developers get to see their code changes immediately, fine-tune their code with incremental changes, debug, explore and deploy their code with ease (both locally and remotely), and ultimately spend more time coding instead of waiting for the dreaded application redeploy to finish. Every time a developer tests a code change it takes minutes to build and deploy the application. JRebel keeps the app server running at all times, so testing is instantaneous and interactive.

  • On-demand Event Event Date: April 22, 2014 Database professionals -- whether developers or DBAs -- can often save valuable time by learning to get the most from their new or existing productivity tools. Whether you're responsible for managing database projects, performing database health checks and reporting, analyzing code, or measuring software engineering metrics, it's likely you're not taking advantage of some of the lesser-known features of Toad from Dell. Attend this eSeminar with Dell Software's …

Most Popular Programming Stories

More for Developers

Latest Developer Headlines

RSS Feeds