Creating and Storing Objects

OOP (Object-oriented programming): programming style where the user:
- declares classes
- create objects from classes
- write programs with interacting objects

Creating and Storing Objects

object: something that can be used in code as an instance variable(state) and a method(behavior).

Dog

State (instance variables):

String name
int age
boolean goodDog

Dog

Behavior (methods):

speak
haveBirthday

class: the template or blueprint from which an object can be created.
- defines what data the object will have and its method
- any class created will use the object’s variables and methods.
  public class ObjectName{
- //instance variables
- //default and parameter constructors
- //accessors and mutators
- //toString and equals
- //behaviors
  }

Instance Variables

An instance variable: is a variable that defines what data your objects will use.
- instance var. are private, meaning methods and classes besides the object-creating class can use the variable unless programmed to.
- While instance variables are declared, they are not given values. The constructors take care of that.
- instance variables are also global variables, and can be freely used throughout your class.

public class Dog {
private int age;
private String name;
private boolean goodDog;
}

Constructors

constructor: when called upon, they create the object by making it public as it saves memory to give values to the instance variables. There is only ONE constructor in a class.
- Constructors do not return any values; they only make space for memory.
- Constructors have no parameters/additional actions, hence their empty parentheses
- Since instance variables are declared out of the constructor, constructors are given the default values for the variables.
```
int age = 0; 
String name = "unknown"; 
boolean goodDog = false; 
```

Parameter Constructors

parameter constructor: serves a similar purpose as a regular constructor, but uses the memory saved from them to add values to the variables. There can be an UNLIMITED amount of parameter constructors in a class.
- have parameters that list the instance variable’s identifier and data type.
- to avoid having similar variable names to the instance variables, the “this” keyword is used.
```
public class Dog
{
   //instance variables here
   //default constructor here

   public Dog(String n, int a, boolean g)
   {
 
      name = n;
      age = a;
      goodDog = g;
 
   }
}
```

Creating Behaviors

methods: behaviors objects can have. They can be public or private depending on what classes you want them to use.