CareerCup

As far as I understanded from the explanation, I write following in java.

import java.util.List;
import java.util.ArrayList;
import java.util.Random;


public class PhoneNumbers {
	
	public static List<Integer> takenNumbers=new ArrayList<Integer>();
	
	public boolean IsNumberTaken(int num){
		
		return takenNumbers.contains(num);
	}
	
	public boolean giveOut(int num){
		
		if(IsNumberTaken(num)){
			
			return false;
		}
		else{ 
			takenNumbers.add(num);
			return true;}
	}
	
	public int getNextNumber(){
		
		Random randomNGen=new Random();
		int generatedN=randomNGen.nextInt(1000);
		while(IsNumberTaken(generatedN)==true){
			generatedN=randomNGen.nextInt(1000);
		}
		takenNumbers.add(generatedN);
		return generatedN;
	}
	
	public void listTakenNumbers(){
		
		System.out.println("Printing taken numbers ");
		for(int i: takenNumbers){
			System.out.println(i);
		}
		
	}
	
	public static void main(String[] args){
		
		PhoneNumbers PN=new PhoneNumbers();
		PN.giveOut(123);
		PN.giveOut(125);
		PN.listTakenNumbers();
		System.out.println("is 123 taken " +PN.IsNumberTaken(123));
		System.out.println("The next number given: " + PN.getNextNumber());
		PN.listTakenNumbers();
		
		
	}

}

Why not just have a counter C that ranges from 000-000-0000 through 999-999-9999. GIVE_ME_ONE will give out C and increment C by one. The other two functions can just compare n to C.