JavaAlgorithms/DataStructures/DynamicArray/DynamicArray.java

package DataStructures.DynamicArray;

import java.util.*;
import java.util.function.Consumer;
import java.util.stream.Stream;
import java.util.stream.StreamSupport;

/**
 * This class implements a dynamic array
 *
 * @param <E> the type that each index of the array will hold
 */
public class DynamicArray<E> implements Iterable<E> {
  private static final int DEFAULT_CAPACITY = 16;

  private int capacity;
  private int size;
  private Object[] elements;

  /**
   * constructor
   *
   * @param capacity the starting length of the desired array
   */
  public DynamicArray(final int capacity) {
    this.size = 0;
    this.capacity = capacity;
    this.elements = new Object[this.capacity];
  }

  /** No-args constructor */
  public DynamicArray() {
    this(DEFAULT_CAPACITY);
  }

  /**
   * Adds an element to the array If full, creates a copy array twice the size of the current one
   *
   * @param element the element of type <E> to be added to the array
   */
  public void add(final E element) {
    if (this.size == this.elements.length) {
      this.elements = Arrays.copyOf(this.elements, newCapacity(2 * this.capacity));
    }

    this.elements[this.size] = element;
    size++;
  }

  /**
   * Places element of type <E> at the desired index
   *
   * @param index the index for the element to be placed
   * @param element the element to be inserted
   */
  public void put(final int index, E element) {
    this.elements[index] = element;
  }

  /**
   * get method for element at a given index returns null if the index is empty
   *
   * @param index the desired index of the element
   * @return <E> the element at the specified index
   */
  public E get(final int index) {
    return getElement(index);
  }

  /**
   * Removes an element from the array
   *
   * @param index the index of the element to be removed
   * @return <E> the element removed
   */
  public E remove(final int index) {
    final E oldElement = getElement(index);
    fastRemove(this.elements, index);

    if (this.capacity > DEFAULT_CAPACITY && size * 4 <= this.capacity)
      this.elements = Arrays.copyOf(this.elements, newCapacity(this.capacity / 2));
    return oldElement;
  }

  /**
   * get method for size field
   *
   * @return int size
   */
  public int getSize() {
    return this.size;
  }

  /**
   * isEmpty helper method
   *
   * @return boolean true if the array contains no elements, false otherwise
   */
  public boolean isEmpty() {
    return this.size == 0;
  }

  public Stream<E> stream() {
    return StreamSupport.stream(spliterator(), false);
  }

  private void fastRemove(final Object[] elements, final int index) {
    final int newSize = this.size - 1;

    if (newSize > index) {
      System.arraycopy(elements, index + 1, elements, index, newSize - index);
    }

    elements[this.size = newSize] = null;
  }

  private E getElement(final int index) {
    return (E) this.elements[index];
  }

  private int newCapacity(int capacity) {
    this.capacity = capacity;
    return this.capacity;
  }

  /**
   * returns a String representation of this object
   *
   * @return String a String representing the array
   */
  @Override
  public String toString() {
    return Arrays.toString(Arrays.stream(this.elements).filter(Objects::nonNull).toArray());
  }

  /**
   * Creates and returns a new Dynamic Array Iterator
   *
   * @return Iterator a Dynamic Array Iterator
   */
  @Override
  public Iterator iterator() {
    return new DynamicArrayIterator();
  }

  private class DynamicArrayIterator implements Iterator<E> {

    private int cursor;

    @Override
    public boolean hasNext() {
      return this.cursor != size;
    }

    @Override
    public E next() {
      if (this.cursor > DynamicArray.this.size) throw new NoSuchElementException();

      if (this.cursor > DynamicArray.this.elements.length)
        throw new ConcurrentModificationException();

      final E element = DynamicArray.this.getElement(this.cursor);
      this.cursor++;

      return element;
    }

    @Override
    public void remove() {
      if (this.cursor < 0) throw new IllegalStateException();

      DynamicArray.this.remove(this.cursor);
      this.cursor--;
    }

    @Override
    public void forEachRemaining(Consumer<? super E> action) {
      Objects.requireNonNull(action);

      for (int i = 0; i < DynamicArray.this.size; i++) {
        action.accept(DynamicArray.this.getElement(i));
      }
    }
  }

  /**
   * This class is the driver for the DynamicArray<E> class it tests a variety of methods and prints
   * the output
   */
  public static void main(String[] args) {
    DynamicArray<String> names = new DynamicArray<>();
    names.add("Peubes");
    names.add("Marley");

    for (String name : names) {
      System.out.println(name);
    }

    names.stream().forEach(System.out::println);

    System.out.println(names);

    System.out.println(names.getSize());

    names.remove(0);

    for (String name : names) {
      System.out.println(name);
    }
  }
}