Objects intro
compound data (fields)

Code developed: Song.java

I will give examples of objects using class Song. Then you'll immediately follow up with the person next to you, for a class Robot.

Review:
Declare a var to hold an int (and draw picture); initialize it (udpate picture).
Declare variable to hold a Foo (and draw picture). Initialize it, presuming that there is a function named new Foo takes in a String and returns a Foo. (update picture)

Data analysis.
a song has an artist, a title, a length, and whether it's copyrighted.

class Song {
  String title;
  String artist;
  double length;  // in seconds.
  boolean isCopyrighted;
}

a robot has an id#, a transformed shape, whether or not it's currently transformed, and whether or not it's evil.

class Robot {
  String id;
  String shape;
  boolean isTransformed;
  boolean isEvil;
}

Fields; picture ("memory diagram").

Constructor, and examples of the data.

Constructors are just functions: You pass them arguments, and they return a value — in particular, they return a newly-constructed object (a Song or a Robot).

Java forces you to write constructors a bit differently than most functions, though:

When writing the signature:
- You don't mention any return-type at all.
  (Conceptually, that's because it's obvious from the fact that it's a constructor: the Song constructor returns something of type Song.)
- The constructor name must be exactly the same as the class name, in Java.
- You don't say static — that's implicit by the fact that it's a constructor.
When calling a constructor, you use the additional keyword new.

For Songs:

class Song extends Object120 {

    String title;
    String artist;
    double length;  // in seconds.
    boolean isCopyrighted;

    
    // define the constructor:
    Song( String t, String a, double l, boolean c ) {
        //some voodoo (for now):
        super(t,a,l,c);
    }
    
    
    static void testSongs() {
        Song s;
        s = new Song( "Help!", "The Beatles", 122, true );
    }
}

declare variables, initializing, full picture.
We'll put these inside your test driver.

to teacher: Reached this far Oct.04.

Using fields.
We'll only get the fields' values for now. (We'll talk about setting fields later (mutation)).
A function taking in an object.
Song: willFit -- given an amount of disk space, is an mp3 verison like to fit within that space?
Robot: canLift -- a robot can lift 3x their own body weight, if *not* transformed.
Song: longer than
Robot: heavier than
a function taking in an object: test cases, header/stub/comments; body.
Syntax review.
You try it: A student, by the the design recipe. We want to keep track of the student's ID, their gender, their major, and their gpa.
Write a function onDeansRoll(Student) (true for students whose gpa is above 3.6).
Write a function inSameMajor. that takes in two Students and checks whether they have the same major.

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Objects intro compound data (fields)

Objects intro
compound data (fields)