Double Variable Class

[hypes057]

How do you create a variable class to hold double values? My String works as I want it to, but I can't figure out how to instance all the double values.

class Item 
{
	public static void main(String args[]) 
	{
	//These are the items values which I want to call itemCosts
	Double itemCoffee = new Double("1.00");
	//Coffe is $1.00
	Double itemWater = new Double("2.00");
	// Water is $2.00
	Double itemMilk = new Double("1.50");
	// Milk is $1.50
	Double itemBagel = new Double("1.25");
	// Bagel is $1.25
	Double itemDonut = new Double("0.75");
	//Donut is $0.75
	//This mess here prints out each item
	System.out.println(itemCoffee); 
	System.out.println(itemWater); 
	System.out.println(itemMilk); 
	System.out.println(itemBagel); 
	System.out.println(itemDonut); 
	
	//This String of items works as I want, it neatly lists
	//each item and its price and uses only 1 println
	String listofItems =
	"Coffee - $1.00 \n"+
	"Water - $2.00 \n"+
	"Milk - $1.50 \n"+
	"Bagel - $1.25 \n"+
	"Donut - $0.75 ";
	System.out.println(listofItems);
	}
}

Also, how do i create a constructor that takes the listofItems String and the (to be created) itemCosts double to initialize the instance variables and also uses get and set methods for each instance?

I know (read: i think) that get and set would be something like:

get itemPrices
set itemPrices

get itemNames
set itemNames

Many thanks in advance!

[Fubarable]

First thing to do is to get rid of your main method and start thinking about true OOP classes.

• Create your class,
• give it a double field (not Double), called price
• give it a String field called itemName
• give it a constructor that takes a String and a double.
• give it getters and setter methods for the price and itemName fields.
• give it ...

[Fubarable]

For example, to get you started:

public class Item {
   private String itemName;
   private double price;
   
   // constructor(s) here
   public Item(String iName, double p) {
      // TODO: add code to finish this
   }   
   
   // TODO: add getters and setters here
   
   // not a main to be seen anywhere in this code!
}

[hypes057]

For example, to get you started:

public class Item {
   private String itemName;
   private double price;
   
   // constructor(s) here
   public Item(String iName, double p) {
      // TODO: add code to finish this
   }   
   
   // TODO: add getters and setters here
   
   // not a main to be seen anywhere in this code!
}

Fubarable,

Thanks for the response. Do you mean something like this?

public class Item 
	{
   private String itemName;
   private double itemPrice;
   
   // constructor(s) here
   public Coffee() 
   {
   String itemName = Coffee
   double = 1.00
   }
   
   public Water() 
   {
   String itemName = Water
   double = 2.00
   }
   
 }

[Fubarable]

No, your constructor has to have the same name as your class. Please reread your chapter on constructors and such.

[hypes057]

No, your constructor has to have the same name as your class. Please reread your chapter on constructors and such.

Yea, thanks. I have re-read almost the entire book, I am not grasping it as well as I had liked. Plus I grasp information better when I am able to ask specific questions as they come.


From your example and last comment, I come up with:

public class Items
{
   private String itemName;
   private double itemPrice;
   
   public Items(String itemName, double itemPrice) 
   {
   itemName = Coffee;
   itemPrice = 1.00;
   }
   
   
      
}

Is that correct?
If that is correct, how do I tell it to grab the String from my original post? Do I enter an itemName and itemPrice for each?

[Fubarable]

You give your constructor the same name as your class, and that part is correct, but the rest of the constructor is wrong.

Let's have a closer look at some of your code:

   // here are your class fields
   private String itemName;
   private double itemPrice;

   // here is your constructor declaration with its two parameters
   public Items(String itemName, double itemPrice) 
   {
     // here is the body of your constructor
     itemName = Coffee;
     itemPrice = 1.00;
   }

In this code there are actually two distinct itemName variables -- the class field called itemName and declared at the top, and the first parameter in your constructor, also called itemName. Within the body of your constructor, the compiler has no way of knowing whcih itemName you are referring to, so it assumes that anything called itemName in the body of the constructor refers to the parameter, and that if you want to refer to the class field, you must use this.itemName.

Currently your constructor changes the values held by the parameter variables to some fixed constant Coffee (I suppose you're trying to use a string here but it's not in quotes -- but even if it were in quotes it would be wrong), and 1.00. But understand that since the constructor parameters disappear into nothingness once program flow leaves the constructor -- once all of its code has been called, this constructor does nothing useful.

Your constructor's goal is to take the values passed in via the parameters and use this to set the class fields. A simple example of what I mean is this:

class Foo {
  private int fooVar;

  public Foo(int fooVar) {
    this.fooVar = fooVar;
  }

}

here I take the value passed into the constructor's fooVar parameter and use it to set the class field. Your constructor should do something similar.

I can then use this to create Foo objects:

class SomeOtherClass {
  public static void main(String[] args) {
    Foo myFoo = new Foo(3);  // passes 3 into the constructor
  }
}

Also, a minor nit-pick: I'd name my class "Item" not "Items" as this class will hold information about one item only. If you have an array of objects of this class, you could call the array variable items as it will hold one or more Item objects.

[hypes057]

Thanks again. I will have to take a bit to read through this and grasp what you are explaining.

[Fubarable]

Much luck!

[Fubarable]

Cross-post: Double Variable Class (Beginning Java forum at JavaRanch)

Please read the link in your cross-post about being forthright when cross-posting. Thanks.