I aware that Java object constructors implicitly initialize their instance's non-static fields. However, I'm unsure of the order that this happens in a class hierarchy. For example:

abstract public class AbstractPieceSequence implements PieceSequence { private Tetromino current; private Tetromino preview; public AbstractPieceSequence() { advance(); } @Override public final void advance() { if (preview == null) { current = getNextPiece(); preview = getNextPiece(); } else { current = preview; preview = getNextPiece(); } } abstract protected Tetromino getNextPiece(); } 

public class ShufflePieceSequence extends AbstractPieceSequence { private List<Shape> bag = new LinkedList<Shape>(); @Override protected Tetromino getNextPiece() { if (bag.size() == 0) { Collections.addAll(bag, Shape.I, Shape.J, Shape.L, Shape.O, Shape.S, Shape.T, Shape.Z); } return Tetromino.tetrominoes.get(bag.remove(0)); } } 

The parent's constructor calls a method in the child class, which throws an exception as the value of List<Shape> bag is currently null.

I can define a child constructor and call super(), but that must be the first line in the constructor body (which means I still don't have a chance to initialize bag before getNextPiece is called).

I am missing something obvious.