ArrayList.java

import java.util.Arrays;

public class ArrayList<E> {
 /**
 * the array which stores the elements of the ArrayList
 */
 private E[] list;
 
 /**
 * the default capacity of the ArrayList
 */
 private final int DEFAULT_CAP = 10;
 
 /**
 * the current capacity of the ArrayList - equivalent to the length of list
 */
 private int capacity;
 
 /**
 * the number of elements in ArrayList
 */
 private int size; 

 /**
 * Constructs an ArrayList of default capacity 10
 */
 @SuppressWarnings("unchecked")
 public ArrayList() {
 list = (E[])new Object[DEFAULT_CAP];
 capacity = 10;
 size = 0;
 }
 
 /**
 * Constructs an ArrayList with a capacity of num
 * @param num the capacity of the ArrayList to be constructed
 */
 @SuppressWarnings("unchecked")
 public ArrayList(int initialCap) {
 list = (E[])new Object[0];
 capacity = initialCap;
 size = 0;
 }
 
 /**
 * Constructs an ArrayList with the elements of the ArrayList passed as parameter - shallow clone
 * @param lst the ArrayList that has the elements the new ArrayList will contain
 */
 @SuppressWarnings("unchecked")
 public ArrayList(ArrayList<E> lst) {
 list = (E[])new Object[lst.size()];
 capacity = lst.capacity;
 size = lst.size;
 for(int i = 0; i < size; i++) {
 list[i] = lst.list[i];
 }
 }
 
 /**
 * Appends an element to the end of the ArrayList
 * @param e the element to append at the end of the ArrayList
 * @return true if the element was successfully appended
 */
 public void add(E e) {
 resize();
 list[size] = e;
 size++;
 }
 
 /**
 * Resizes the ArrayList if the number of elements it contains is equal
 * to its capacity
 */
 @SuppressWarnings("unchecked")
 private void resize() {
 int newCap = Math.max(capacity*2, DEFAULT_CAP);
 if(size < list.length) return;
 
 Object[] temp = new Object[newCap];
 for(int i = 0; i < list.length; i++) {
 temp[i] = list[i];
 }
 list = (E[])temp;
 capacity = newCap;
 }
 
 /**
 * Inserts an element at the specified index, pushes the current 
 * elements at and after the insertion point back
 * @param index the index where the element will be inserted into
 * the ArrayList
 * @param e the element to be inserted
 */
 public void add(int index, E e) {
 resize();
 for(int i = size-1; i >= index; i--) {
 list[i+1] = list[i];
 }
 list[index] = e;
 size++;
 }
 
 /**
 * Creates a new, empty ArrayList of the same capacity it had
 * previously
 */
 @SuppressWarnings("unchecked")
 public void clear() {
 list = (E[])new Object[capacity];
 size = 0;
 }
 
 /**
 * Clones the current ArrayList and returns it
 */
 public ArrayList<E> clone() {
 ArrayList<E> temp = new ArrayList<E>();
 temp.size = this.size;
 temp.capacity = this.capacity;
 temp.list = Arrays.copyOf(this.list, this.list.length);
 return temp;
 }
 
 /**
 * Checks if the ArrayList contains an object
 * @param o the object to check
 * @return true if the ArrayList contains o, false otherwise
 */
 public boolean contains(Object o) {
 for(int i = 0; i < size; i++) {
 if(list[i].equals(o)) return true;
 }
 return false;
 }
 
 /**
 * Returns the element at a specified index of the ArrayList
 * @param index the index of the element to return
 * @return the element at index
 */
 public E get(int index) { 
 return (E)list[index];
 }
 
 /**
 * Finds the index of an Object in the ArrayList
 * @param o the object
 * @return the index of o if it is in the ArrayList, -1 if it 
 * is not in the ArrayList
 */
 public int indexOf(Object o) {
 int index = -1;
 for(int i = 0; i < size; i++) {
 if(list[i].equals(o)) {
 index = i; break;
 }
 }
 return index;
 }
 
 /**
 * Checks if the ArrayList is empty
 * @return true if the ArrayList contains no elements,
 * false otherwise
 */
 public boolean isEmpty() {
 return size == 0;
 }
 
 /**
 * Finds the last index of object o
 * @param o the object
 * @return the last index of o in the ArrayList, -1 if
 * it is not in the ArrayList
 */
 public int lastIndexOf(Object o) {
 int index = -1;
 for(int i = 0; i < size; i++) {
 if(list[i].equals(o)) index = i;
 }
 return index;
 }
 
 /**
 * Removes the element at the specified index, shifts the 
 * following elements accordingly
 * @param index to remove
 * @return the element that is removed
 */
 public E remove(int index) {
 if(index > size) return null;
 E element = null;
 for(int i = index+1; i < size; i++) {
 list[i-1] = list[i];
 }
 list[size-1] = null;
 size--;
 return element;
 }
 
 /**
 * Removes the specified object from the ArrayList
 * @param o the object to remove
 * @return true if the Object is successfully, false otherwise
 */
 public boolean remove(Object o) {
 int index = indexOf(o);
 if (index == -1) return false;
 remove(index);
 return true;
 }
 
 /**
 * Sets the element at the specified index to the given element
 * @param index the index to set the new element
 * @param element the new element
 * @return the element that was previously at the given index
 */
 public E set(int index, E element) {
 if(index < 0 || index >= size())
 throw new IndexOutOfBoundsException();
 E currentElement = get(index);
 list[index] = element;
 return currentElement;
 }
 
 /**
 * Returns the number of elements in the ArrayList
 * @return size - how many elements the ArrayList contains
 */
 public int size() {
 return size;
 }
 
 /**
 * Returns a sublist of the current ArrayList
 * @param fromIndex the beginning of the subList
 * @param toIndex the end of the subList
 * @return a new ArrayList with a shallow copy of the elements
 * from the index fromIndex to the index toIndex
 */
 public ArrayList<E> subList(int fromIndex, int toIndex) {
 ArrayList<E> temp = new ArrayList<E>();
 for(int i = fromIndex; i< toIndex; i++) {
 temp.add(this.get(i));
 }
 return temp;
 }
 
 /**
 * Returns the elements of the ArrayList in an array
 * @return an array containing a shallow copy of the elements
 * in ArrayList
 */
 public Object[] toArray() {
 Object[] arr = new Object[size];
 for(int i = 0; i < this.size; i++) {
 arr[i] = this.get(i);
 }
 return arr;
 }
 
 
 public String toString() {
 if(size == 0) return "[]";
 String str = "{" + list[0];
 for(int i = 1; i < size; i++) {
 str = str + ", " + list[i];
 }
 str = str + "]";
 return str;
 
 }
 

 

}