Using inheritance and composition

• Inheritance is used for
  
• Code resuse
• To support polymorphism
• Disadvantages of inheritance
• Difficult to change the interaface of the subclass
• Superclass is always instantiated
  
• Can get complex and unmanageable
• Composition is used for code reuse
• Disadvantages of composition
• We cannot use polymorphism
• We cannot extend the system by adding subclasses
• May have a slight performance overhead
• Usage
• Inheritance: IS- A
• Composition: HAS - A
  

Example 1:  public class Car {     private Engine engine;     public void start() {}     public void stop() {} }  public class SUV extends Car{     public void start() {} //overrides the start method from Car       public void fourByFourMode() {} } Example 2: public void someMethod() {     Car c = new SUV();     c.start(); } Example 3: public class Car {     private Engine engine;     public void start() {       engine.start();         //maybe do something more     }     public void stop() {} }

Java2html

Resources:

1. Compostion vs. Inheritance
   
2. Composition and interfaces

Note: This post was originally posted on my blog at http://www.adaptivelearningonline.net