The code here: http://graphics-geek.blogspot.com/2013/09/lazy-lists.html compared in Java and Scala.

gistfile1.java

// Java:
public class LazyListManager {

    public static <T> List<T> add(List<T> list, T item) {
        if (list == null) {
            list = new ArrayList<T>();
            list.add(item);
        } else if (!list.contains(item)) {
            list.add(item);
        }
        return list;
    }

    public static <T> List<T> remove(List<T> list, T item) {
        if (list != null) {
            list.remove(item);
            if (list.isEmpty()) {
                list = null;
            }
        }
        return list;
    }
}

class LazyLists {
    List<Integer> intList = null;
    List<Float> floatList = null;

    public void addItemBetter(int item) {
        intList = LazyListManager.add(intList, item);
    }

    public void removeItemBetter(int item) {
        intList = LazyListManager.remove(intList, item);
    }

    public void addItemBetter(float item) {
        floatList = LazyListManager.add(floatList, item);
    }

    public void removeItemBetter(float item) {
        floatList = LazyListManager.remove(floatList, item);
    }
}

// Scala:
class LazyLists {
    lazy val intList: List[Int] = new ArrayList[Int]()
    lazy val floatList: List[Double] = new ArrayList[Double]()
        
    def addItemBest(item: Int): Unit = intList.add(item)
    def addItemBest(item: Double): Unit = floatList.add(item)
    def removeItemBest(item: Int): Unit = intList.remove(item.asInstanceOf[Object])
    def removeItemBest(item: Double): Unit = floatList.remove(item)
}