ArrayList.java

package datastructure.array;

import java.util.Arrays;

import datastructure.Iterator;
import datastructure.List;

public class ArrayList implements List {

    private int size = 0;

    private Object[] elementData = new Object[100];

    @Override
    public void add(Object o) {
        ensureCapacity(size + 1);
        elementData[size++] = o;
    }

    private void ensureCapacity(int size) {
        if (size > elementData.length) {
            grow();
        }
    }

    private void grow() {
        elementData = Arrays.copyOf(elementData, size * 2);
    }

    @Override
    public void add(int index, Object o) {
        rangeCheckForAdd(index);
        ensureCapacity(size + 1);
        System.arraycopy(elementData, index, elementData, index + 1, size - index);
        elementData[index] = o;
        size++;
    }

    private void rangeCheckForAdd(int index) {
        if (index < 0 || index > size) {
            throw new IndexOutOfBoundsException();
        }
    }

    @Override
    public Object get(int index) {
        rangeCheck(index);
        return elementData[index];
    }

    private void rangeCheck(int index) {
        if (index >= size || index < 0) {
            throw new IndexOutOfBoundsException();
        }
    }

    @Override
    public Object remove(int index) {
        rangeCheck(index);
        Object dest = elementData[index];
        System.arraycopy(elementData, index + 1, elementData, index, size - index - 1);
        size--;
        return dest;
    }

    @Override
    public int size() {
        return size;
    }

    public Iterator iterator() {
        return new Iterator() {

            private int index = 0;

            @Override
            public Object next() {
                return elementData[index++];
            }

            @Override
            public boolean hasNext() {
                return index < size;
            }
        };
    }

}