Class vs Object

Hi,

You're absolutely right a class is the instructions on how to build an object and object is the result of running that code..... this blew my mind when I first got into coding.

The best example I ever heard was Lego, the mould that makes the lego piece would be the class, this is the code you write which says how the object (piece of Lego) should act and what values the piece should have (state) such as number of bumps and colour etc. The Lego piece on the other hand is the actual object and when you call methods on this object you potentially change or get at the state of that object (there are other things such as static methods which effect the entire class, and other bits and bobs which are pointless explaining right now).

Every single line of code you write in Java is within an object, Java is very strict and unlike some other languages you can't write anything outside of a class so you're using them all the time right now.

To give you some code to explain the Lego scenario above see the below

public class Lego{

    private int mNumberOfBumps;
    private Colour mColour; //Notice how this is another class!! we can even use classes inside other classes

    public Lego(){
        //This is a constructor and is the code we run when we say that we want to make a new Lego Piece
        mNumberOfBumps = 4;
        mColour = Colour.Blue //This is just an example so ignore the fact that there is no Colour class
    }


    public int getNumberOfBumps(){
    //this is a method which we can call on any OBJECT we create from this class to give us some information about the 
   //state of the object
        return mNumberOfBumps;
    }
}

//Somewhere else in our code we can write

Lego legoPiece = new Lego(); //This runs the construtor function which is a special function and creates a new Lego //object which we assign to a variable called legoPiece.

//This object can then run the methods of the class as needed
int howManyBumpsDoYouHave = legoPiece.getNumberOfBumps();

I hope this helps in what is a fairly hard concept to grasp, once it clicks though you'll see this makes programming so much easier and allows you to write smaller chunks of code to make even the largest problem attainable with smaller chunks breaking down the problem so you can visualise it easy.

Daniel