• 闲话少说, 原理大家都懂, 直接上代码

/*** 手写一个ArrayList* @param <E>*/
public class MyArrayList<E> {/*** 当前存储的容量*/private int size;/*** 存放对象的数组*/private Object[] objects;/*** 数组初始容量*/private static final int INITIAL_SIZE = 16;public MyArrayList() {// 初始化数组objects = new Object[INITIAL_SIZE];}/*** 当前存储的元素容量*/public int size() {return size;}public boolean add(E e) {if (size == objects.length) {// 扩容transferArr();}objects[size] = e;size++;return true;}/*** 指定位置插入元素* @param index* @param e* @return*/public boolean add(int index, E e) {if (index >= size) {throw new ArrayIndexOutOfBoundsException();}if (size == objects.length) {transferArr();}System.arraycopy(objects, index, objects, index + 1, size - index);objects[index] = e;size++;return true;}/*** 数组扩容*/private void transferArr() {int length = objects.length;int half = length >> 1;length = length + half;Object[] newArr = new Object[length];System.arraycopy(objects, 0, newArr, 0, objects.length);objects = newArr;}public E get(int index) {if (index < 0 || index >= size) {throw new ArrayIndexOutOfBoundsException();}return (E) objects[index];}/*** 删除元素*/public E remove(int index) {if (index < 0 || index >= size) {throw new ArrayIndexOutOfBoundsException();}Object object = objects[index];if (index == (size - 1)) {objects[index] = null;} else {System.arraycopy(objects, index + 1, objects, index, size - index);}size--;return (E) object;}/**修改元素, 返回旧的元素*/public E set(int index, E e){if (index < 0 || index >= size) {throw new ArrayIndexOutOfBoundsException();}Object oldVal = objects[index];objects[index] = e;return (E) oldVal;}public int arrLength() {return objects.length;}}

• 参考文献
  jdk源码