Lazy Fibonacci in Java!

LazyList.java

package de.lenabrueder;

import java.util.ArrayList;
import java.util.List;
import java.util.function.Function;
import java.util.function.Supplier;

public class LazyList<T> {
    final T head;
    LazyList<T> tail = null;
    Supplier<LazyList<T>> tailSupplier;

    public LazyList(T head, Supplier<LazyList<T>> tail) {
        this.head = head;
        this.tailSupplier = tail;
    }

    public T getHead() {
        return head;
    }

    public <B> LazyList<Pair<T,B>> zip(LazyList<B> b) {
        return new LazyList<Pair<T, B>>(new Pair<T,B>(this.head, b.head), () -> this.getTail().zip(b.getTail()));
    }

    public <B> LazyList<B> map(Function<T,B> f) {
        return new LazyList<B>(f.apply(this.head), () -> this.getTail().map(f));
    }

    public List<T> take(int n) {
        List<T> list = new ArrayList<>(n);
        LazyList<T> el = this;
        for (int i=0; i<n; i++) {
            list.add(el.head);
            el = el.getTail();
        }

        return list;
    }

    public void setTail(Supplier<LazyList<T>> tail) {
        this.tailSupplier = tail;
    }

    public LazyList<T> getTail() {
        if (tail == null) {
            tail = tailSupplier.get();
            tailSupplier = null;
        }
        return tail;
    }

    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder();
        sb.append(head.toString());
        LazyList<T> _tail = tail;
        while (_tail != null) {
            sb.append(", ");
            sb.append(_tail.getHead());
            _tail = _tail.tail;
        }
        return sb.toString();
    }
}

Main.java

package de.lenabrueder;

import java.util.List;

public class Main {

    public static void main(String[] args) {
	LazyList<Long> fibs = new LazyList<>(0L,
                () -> new LazyList<>(1L,
                        null    //TODO: workaround for "not initialized" and "effectively-final", see below
                )
        );
	fibs.getTail().setTail(() -> fibs.zip(fibs.getTail()).map(p -> p.getA() + p.getB()));
        List<Long> realFibs = fibs.take(20);

        System.out.println(realFibs);
    }
}

Pair.java

package de.lenabrueder;

public class Pair<A,B> {
    A a;
    B b;

    public Pair(A a, B b) {
        this.a = a;
        this.b = b;
    }

    public A getA() {
        return a;
    }

    public B getB() {
        return b;
    }
}