FibonacciSequence.java

import java.util.Iterator;

public class FibonacciSequence implements Iterator<Long> {
  private long n = 0;
	private long a = 0;
	private long b = 1;
	public boolean hasNext() { return a + b > 0; }
	public Long next() {
		long fib;
		if(n == 0 || n == 1) {
			fib = n;
		}
		else {
			fib = a + b;
			a = b;
			b = fib;
		}
		n++;
		return fib;
	}
	public void remove() {}

	public static void main(String[] args) {
		FibonacciSequence fs = new FibonacciSequence();
		for(int i = 0; i < 10 && fs.hasNext(); i++){
			System.out.println(fs.next());
		}
	}
}

Taker.java

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

public class Taker<T> {
  public List<T> take(int n, Iterator<T> xs) {
    List<T> taken = new ArrayList<T>();
    for (int i = 0; xs.hasNext() && i < n; i++) {
      taken.add(xs.next());
    }
    return taken;
  }
  
  public static void main(String[] args) {
  List<Long> fibonacciUpto25 = new Taker<Long>().take(25, new FibonacciSequence());
	System.out.println(fibonacciUpto25);
  }
}