Exercises for Nested Classes

The answer is below

public class DataStructure {

  private final static int SIZE = 15;
  private int[] arrayOfInt = new int[SIZE];

  DataStructure(){
    for (int i = 0; i < SIZE; i++)
      arrayOfInt[i] = i;
  }

  public int getSize(){
    return SIZE;
  }

  public int getInt(int index){
    return arrayOfInt[index];
  }

  // interface is default static
  interface DataStructureIterator extends Iterator<Integer>{}

  // non-static nested class(inner class), like an instance method
  private class EvenIterator implements DataStructureIterator{

    private int nextIndex = 0;

    @Override
    public boolean hasNext() {
      return nextIndex < SIZE;
    }

    @Override
    public Integer next() {
      Integer value = Integer.valueOf(arrayOfInt[nextIndex]);
      nextIndex += 2;
      return value;
    }
  }

  public DataStructureIterator getEventIterator(){
    return new EvenIterator();
  }

  public void printEven(){
    DataStructureIterator iterator = new EvenIterator();
    while (iterator.hasNext())
      System.out.print(iterator.next() + " ");
    System.out.println();
  }

  // more generic print method, through an interface type parameter
  public void print(DataStructureIterator iterator){
    while (iterator.hasNext())
      System.out.print(iterator.next() + " ");
    System.out.println();
  }

  // pass a functional interface type parameter, for lambda expression invoking
  public void print(Function<Integer, Boolean> function){
    for (int i = 0; i < SIZE; i++){
      if (function.apply(i)) // like a filter
        System.out.print(arrayOfInt[i] + " ");
    }
    System.out.println();
  }

  // as a method reference, for substitution of lambda expression
  public static Boolean isEvenIndex(Integer index){
    if (index % 2 == 0) return Boolean.TRUE;
    return Boolean.FALSE;
  }

  public static Boolean isOddIndex(Integer index){
    if (index % 2 == 0) return Boolean.FALSE;
    return Boolean.TRUE;
  }

  public static void main(String[] args) {

    DataStructure ds = new DataStructure();

    System.out.println("printEven()");
    ds.printEven();

    System.out.println("print(DataStructureIterator) with getEvenIterator()");
    ds.print(ds.getEventIterator());

    System.out.println("print(DataStructureIterator) with an instance of EventIterator");
    ds.print(ds.new EvenIterator());

    System.out.println("print(DataStructureIterator) with anonymous class, odd index");
    ds.print(new DataStructureIterator() {
      private int nextIndex = 1;
      public boolean hasNext() {
        return nextIndex < ds.getSize();
      }
      public Integer next() {
        Integer value = Integer.valueOf(ds.getInt(nextIndex));
        nextIndex += 2;
        return value;
      }
    });

    System.out.println("print(Function) with lambda expression, even index");
    ds.print(index -> index % 2 == 0 ? true : false);
    ds.print(index -> index % 2 == 0 ? false : true );

    System.out.println("print(Function) with method references");
    ds.print(DataStructure::isEvenIndex);
    ds.print(DataStructure::isOddIndex);
  }
}

reference from: https://docs.oracle.com/javase/tutorial/java/javaOO/QandE/nested-questions.html