Datatype of a class?

[Skipito]

Hello,

What does a datatype of a class mean? What can I do with it? I have seen many datatypes that have the class' name instead of int or something similar. I also have seen arrays with as datatypes the class' name..

For example this:

class JustAClass {
    
  Vehicle haha; //Why is this posible?! What can I do with it?
   
}

class Vehicle {

    public static void main(String args[]) {
 
       
    
 }
}

What can I do with the ''vehicle'' datatype I typed in JustAClass?

I did a Google Search, and unfortunately didn't find enough helpful information. Does anybody know the name of this ''using a class as datatype''?

Thank you.

[hemant_metalia]

Hi Skipito

when you create a class it is a custom datatype then you can create variable(object) same as datatypes like int,Integer and so on...
So Vehicle written in your class is a class written some where else.

as if i create class myDataType then i can use myDataType class as follow

public class myDataType{
int a;
}
public class sample{
public static void main(STring a[]){
myDataType a;
}
}

[Skipito]

Thank you very much for your reply.

However, I still don't get the 'use' of this code. I mean, what can you do with the 'Datatype a' now? I cant declare the variable in the sample class.

[Fubarable]

However, I still don't get the 'use' of this code. I mean, what can you do with the 'Datatype a' now?

You can use it in the JustAClass's constructor and instance methods once you've instantiated the haha variable either by having it refer to a new Vehicle instance or some other already existing instance. Right now haha has been declared but not constructed yet and so it refers to nothing; it is null.

I cant declare the variable in the sample class.

what do you mean "I can't declare the variable in the sample class"?

[hemant_metalia]

Hi Skipito

First of all you need to know why we create a class ?
we create a class to combine variables and operations on it.

as example if you want to create rectangle you need x and y axes so combine them to a class rectangle and then operations like draw rectangle,moverectangle etc...

class Rectangle{
     long x;
     long y;
     public rectangle(long x1,long y1){
            x=x1;
            y=y1;
     }
     public void drawRectangle(){
      //code to draw rectangle
     }
     public void moveRectangle(){
      //code to move rectangle
     }

}

//now you can use rectangle datatype and its operations

public class sample{
          public static void main(String a[]){
                      Rectangle r1=new Rectangle(5,50);
                       r1.drawRectangle();//this will draw a rectangle
                       r1.moveRectangle();//this will move the rectangle
             }
}

[Skipito]

Thanks for the comments.

So basically, the above code where you say: ''Rectangle r1'', is where you declare a object for the class Rectangle? Right?
So what I did in my example in the first post: ''vehicle haha'' is declaring an object called haha for class vehicle right?
So basically its connecting 2 classes via objects?

Thanks mates!!!