Notes for Engineers

Inheritance

• Reusable code, maintain the code easier
  
• Implemented by using 'extend' keyword
  
• Hierarchy of classes
  
  • Parent, grandparent, ancestor (super)
    
  • Child, grandchild, descendant
    
  • Inheritance uses parent etc
    
  • Models a IS A relationship
    
  • Child class inherits the methods defined in parent class
    
  • Private data fields in parent class are not accessible by name only
    
    • Need getters and setters
      
  • Private methods are NOT available
    
  • Methods in child class OVERRIDES same method in parent class with same name
    
  • Overriding
    
    • Child class has same method with same signature as method in Parent class
      
      • Same name
        
      • Same type
        
      • Same return, order of parameters, just all same
        
    • If same method in class B and same class with same parameters in class A, then the class B method is run!
      
      • Unless a SUPER call is put inside the class B method
        
    • To prevent a override -
      
      • Use FINAL in parent class
        
    • Rules on Inheritance
      
      • Child classes may NOT remove attributes (instance fields) or methods
        
      • Public parent methods cannot override private child class methods
        
      • Multiple inheritance not supported in Java
        
      • Parent (base) class cannot inherit from child class
        
      • Every class automatically inherits from OBJECT
        
    • Derived Classes can
      
      • Inherit method
        
      • Override method
        
        • Supply a different public implementation of a method that exists in the base class
          
      • Overload method
        
        • Supply a method with the same name as method that exists in the base class BUT change the signature!
          
      • Add method
        
    • Derived classes can
      
      • Inherit field: all friends from superclass are automatically inherited, even though they might not be visible
        
      • Add field: supply new field that does not exist in base class