Thread: how to create multiple objects

Hello,

i need help on who to create multiple objects

i provide a part of the code, what i need is to create, for example, 25 Cartons.

How can i implement this faster (?) without writing 25 times :

"
Carton carton1 = new Carton(numBags);
Carton carton2 = new Carton(numBags);
Carton carton1 = new Carton(numBags);
....
Carton carton25 = new Carton(numBags);
"

public class Programm{
    protected int numCartons; //number of Cartons. 25 cartons
    protected int numBags;     //number of Bags in Cartons. 2 bags per carton
 
    public Programm(int numCartons, int numBags){
        this.numCartons= numCartons;
        this.numBags = numBags;
    }
 
  public void createCartonsWithBags(int numBags){
       Carton carton1 = new Carton(numBags);
       Carton carton2 = new Carton(numBags);
       Carton carton3 = new Carton(numBags);
       //....
       Carton carton25 = new Carton(numBags);
  }
 
  public static void main(String[] argv ){
          int numCartons = 25;
	  int numBags= 2;
 
	  Myprogram m = new Myprogram(numCartons , numBags);
	  m.createCartonsWithBags(numCartons);
  }
}

use array's..

 Carton[] cartons = new Carton[25];

Originally Posted by arieltal

use array's..

 Carton[] cartons = new Carton[25];

This will only create an array variable filled with nulls. You will still need to use a for loop to fill the array with Carton objects.

2 questions :

1) I forgot to write that i want a vector. I mean that the number of Cartons objects should be determined dynamically.
The question here is that i would like you to see the code and tell me if what i have done is correct with the vector.
Is it ok or not ?


2) I want to print the message, from method cartonPrint() in Carton class, in createCartonsWithBags() method.
I need help here. Any idea ?

I provide code below, what i have tried so far :

import java.util.Vector;
 
public class Programm{
    protected int numCartons;  //number of Cartons.
    protected int numBags;     //number of Bags in Cartons.
 
	public Vector<Carton> carton; //is this correct ???
 
    public Programm(int numCartons, int numBags){
        this.numCartons= numCartons;
        this.numBags = numBags;
    }
 
  public void createCartonsWithBags(int numBags){
       carton = new Vector<Carton>(25); // is it correct ???
 
	   /* i want to print the message from method cartonPrint() in Carton class.  */ 
	   for(int i=0; i< carton.size(); i++){
			carton[i].cartonPrint(); // i need Help here.
	   }
  }
 
  public static void main(String[] argv ){
      int numCartons = 25;
	  int numBags = 2;
 
	  Programm m = new Programm(numCartons, numBags);
	  m.createCartonsWithBags(numBags);
  }
}

import java.util.Vector;
 
public class Carton{
  protected int numBags; 
 
  public Carton(int numBags){
      this.numBags = numBags;
  }  
 
  public void cartonPrint(){
	System.out.println("Carton number "); 
  }
}

Originally Posted by dominco

2 questions :

1) I forgot to write that i want a vector. I mean that the number of Cartons objects should be determined dynamically.
The question here is that i would like you to see the code and tell me if what i have done is correct with the vector.
Is it ok or not ?

regarding

public Vector<Carton> carton; //is this correct ???

This looks good. Just a personal nitpic, but I'd name the variable cartons because it will hold references to more than one Carton object.

regarding

  public void createCartonsWithBags(int numBags){
       carton = new Vector<Carton>(25); // is it correct ???

This also looks good, although again I'd name the variable cartons. Note that you don't have to pass an int into the Vector constructor, but it does make it work more efficiently if you tell it on creation your best estimate of its likely size.

regarding:

	   /* i want to print the message from method cartonPrint() in Carton class.  */ 
	   for(int i=0; i< carton.size(); i++){
			carton[i].cartonPrint(); // i need Help here.
	   }

Here you've got several problems.

First of all you're trying to treat a Vector as if it were an array. It isn't so you can't use array index notation to get items out of the Vector. Instead you must use methods that the Vector has such as its get(int i) method.

But more importantly, you're trying to call a method on a Carton object before it's been created. Think of an array or ArrayList or Vector as being similar to an empty egg carton. You don't have any eggs in it until you first put them in there. So use a for loop and add Carton objects into your Vector using its add(...) method. Only then can you use Carton objects that the vector might hold.

Please Google for an ArrayList tutorial and check the API. You're still not adding any objects to the list, you're still guessing at how to work with Lists, and you're not using any of the methods that are available for the list. The API will tell you what methods are available for this class and you need to learn to use it.

OK, thanks i ll check the generics in java the List, ArrayList and if have any question i ll ask here, because i have no where else to ask.