🪴 Quartz 4.0

Lesson 10: Introduction to Writing Classes 1

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Instance Variables:

  • Located outside of any method
  • Represents instance data
  • Allows data to be modified and accessed by any method in the class
  • Data is different depending on the object

Visibility Modifiers:

Public:

Allows external classes to modify instance variables

Private and Encapsulation:

Encapsulation: The idea that only a class should be able to modify its own instance variables

  • Private variables enforce Encapsulation, only being able to be modified by the class that they are apart of
public class example {
  private int a;
}

Testing Objects:

You can create a main method and create objects inside of a class in order to check for errors

public class test {
  private int a;
  private bool b;
  
  //Test Method
  public static void main(String[] args) {
    testObject = new test();
  }
}

Constructors:

Create new objects and gives value to their instance variables

Default Constructors:

Every class has a default constructor and gives default values based off the data type:

Type:Default Value
Numeric Primitive Types0
booleanfalse
class(object)null

Writing Custom Constructors:

  • Allows us to input custom values into instance variables
  • Is public in order to allow other classes to create objects of this class
  • Only method that doesn’t have a return type
  • Name is the same as the class
public class exampleC {
  private int myNum;
  private bool allowed;
  
  //Constructor
  public example(int newNum, bool choice) {
    myNum = newNum;
    allowed = choice;
  }
}

Calling Constructors:

Once a Custom Constructor is created, the default one becomes unavailable 

//Using class exampleC from above
//Code below is in another class/file
 
exampleC myExample = new exampleC(); //Default Constructor, values are 0 and false
exampleC myExample2 = new exampleC(5, true); //Custom Constructor, value are 5 and true

Methods:

Instance Methods:

  • Not static, unlike normal methods
  • Can only be called on an object of the method’s class
  • Interface: The collective public methods of a class
public int instanceMethod() {
}

Helper Method:

  • Private and used internally by one or more other methods
  • Improves modularity and Code reusability
public int instanceMethod() {
    //Helper Method
    private static void HelperMethod(){
    }
}

Static Variables, Constants, and Methods:

A static method can't directly access a non-static member

The keyword static makes a constant/variable/method shared among all objects of a class

  • Saves memory
  • Stores data between objects
  • Use when you don’t want to store data for only a specific instance

Math.random:

The Math.random() method is used to return a random number within a given range

//Expression
(int)(Math.random() * ((max - min) + 1)) + min;
//max is the highest possible generated number
//min is the lowest possible generated number;

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