Base.java

public class Base {
  protected List<Cell> cells = new ArrayList<>();
  protected Matrix matrix;
  
  public Base(Matrix matrix) {
    this.matrix = matrix;
    for(int i = 0; i < matrix.dimension(); ++i)
      // This call won't work, because Row.row isn't set until after the call to super(matrix);
      this.cells.add(this.getCell(i));
  }
  
  public abstract Cell getCell(int i);
}

Row.java

public class Row {
  private int row;
  public Row(int row, Matrix matrix) {
    super(matrix);
    this.row = row;
  }
  
  public Cell getCell(int i) {
    return this.matrix.getCell(row, i);
  }
}