Datatype of a class?

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:

Code:

---


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.

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

Code:

---

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

---

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.

Quote:

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Originally Posted by Skipito

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.

Quote:

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I cant declare the variable in the sample class.

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

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...

Code:

---

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
            }
}

---

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!!!