• Homework Solution
• Classes
• Aggregation
• Constructors
• Encapsulation
• Access Modifiers
• Static & Final
• Inheritance

• A Class is a combination of state and behavior
• State: Class properties
• Behavior: Class methods

• An Object is an instance of a Class
• Class is a "blueprint" to build an Object

• Properties
• int height
• int depth
• int width
• Methods
• int volume()
• String toString()

• "has-a" relationship
• One Class contains an instance of another Class

 Class Starship {
     int warpSpeed;
     int distanceTraveled;
     CrewMember [] crew;
     CrewMember captain;
     public boolean travelTo(int xCoord, int yCoord, int zCoord);
     public void teleport(CrewMember crewMember);
 }

 Starship enterprise = new Starship();
 CrewMember spock = new CrewMember();
 enterprise.teleport(spock);
     

• Properties
• double lat
• double long
• Methods
• void set(double lat, double lng)
• String toString()

• Java provides a default constructor
• ie. Furniture()
• Best practice to pass required parameters through constructor

 //Furniture constructor 
 public Furniture(int height, int width, int depth) {
     //set properties
 }

 //Table constructor use
 Furniture t = new Furniture(3, 5, 3);
 System.out.println(t.volume());

• Constructor has the same name as the Class
• No return value is declared
• It can have arguments
• Once you define a constructor, Java does not provide a default

• Concept of restricting access to Class properties by making them private and allowing public access through public methods
• Very common practice in Java

 Class Starship {
     private int numberOfCrewMembers;
     private int crewLimit = 15;

     public void setNumberOfCrewMembers(int crew) {
          if(crew <= crewLimit)
               numberOfCrewMembers = crew;
     }
 }             

• Access Modifiers are used to expose behavior that is useful to the user of a Class.
• public
• Anyone can read or write the property or execute the method
• protected
• Only sub-classes can read or write the property or execute the method.
• private
• Only the current Class can read or write the property or execute the method.

• static
• Variable/Method isn't tied to an Object instance
• Modifies a variable/method to be at Class level
• final
• Variables can only be set once
• Method can only be defined once (Can't be overridden)
• Classes can't be overridden or extended

 public static int aNumber = 3;
 public static String convertString(String word);

 public final int anotherNumber = 2;
 public final void finalMethod(int number);
 public final class SomeClass{  }