how to initialise set in a constructor

davie · #1 (**permalink**) 12-03-2010, 07:54 PM

Hi, I need to initialise a set in the constructor. I have a set that already contains some values called "numbers" but I need to initialise this set called "newNumbers" with the same values in the constructor. The code I have tried is:

Java Code

 public PhoneBook()
  {
     super();
     this.newNumbers = new TreeSet<Integer>();
     this.newNumbers = numbers;
}

im a complete novice so im probably going about this the wrong way.

Thankyou in advance to anyone willing and able 2 help.

helloworld922 · #2 (**permalink**) 12-03-2010, 08:19 PM

That's not enough information for us to figure out what is wrong. Is the variable numbers being setup in the super constructor, or is it being passed to your constructor for duplicating? Do you want to create a new set with the identical values, or do you want to use the same object and just reference it?

Also, as a sidenote I take it newNumbers contains phone numbers, right? I know that it's not likely there is a number that starts with 0, but it is possible. A better method of storing phone numbers is with a String object.

davie · #3 (**permalink**) 12-03-2010, 08:27 PM

thankyou for your response, I want to create a new set containing the numbers that which are being passed for duplication. The numbers are just single numbers not actual phone numbers and there are no 0's..

helloworld922 · #4 (**permalink**) 12-03-2010, 09:35 PM

Ah. Ok, so what you will need to do is first of all put a parameter for your constructor that gives it the original list of numbers.

Java Code

public PhoneBook(TreeSet<Integer> numbers)

The TreeSet class has a convenient constructor that will add all of the elements of a Collection into it in natural order (aka. sorted). Simply call that constructor, passing your numbers as a parameter and it will automatically create your new TreeSet with the numbers in it. On a side note, I'm not completely positive if it clones each element or just uses the reference, but because Integers are immutable, I don't think it matters here.

Java Code

TreeSet<Integer> newSet = new TreeSet<Integer>(numbers);

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