027_自己实现一个ArrayList

import java.util.Arrays;

/**
 * 自定义ArrayList
 */
public class MyArrayList {
	private Object[] elementData = {};
	private int size;
	
	/**
	 * 构造方法
	 */
	public MyArrayList() { }
	
	/**
	 * 数组大小
	 * @return
	 */
	public int size() {
		return size;
	}
	
	/**
	 * 数组是否为空
	 * @return
	 */
	public boolean isEmpty() {
		return size == 0;
	}
	
	/**
	 * 扩容
	 * @param minCapacity
	 */
	private void grow(int minCapacity) {
		if(minCapacity - elementData.length > 0) {
			int oldCapacity = elementData.length;
			int newCapacity = oldCapacity + (oldCapacity >> 1);
			if(newCapacity - minCapacity < 0) {
				newCapacity = minCapacity;
			}
			elementData = Arrays.copyOf(elementData, newCapacity);
		}
	}
	
	/**
	 * 检测下标是否越界
	 * @param index
	 */
	private void checkRange(int index) {
		if(index >= size || index < 0) {
			throw new IndexOutOfBoundsException();
		}
	}
	
	/**
	 * 添加元素到末尾
	 * @param o
	 * @return
	 */
	public boolean add(Object o) {
		grow(size + 1);
		elementData[size++] = o;
		return true;
	}
	
	/**
	 * 添加元素到指定位置
	 * @param index
	 * @param o
	 */
	public void add(int index, Object o) {
		if(!(index <= size && index >= 0)) {
			throw new IndexOutOfBoundsException();
		}
		
		grow(size + 1);
		System.arraycopy(elementData, index, elementData, index + 1, size - index);
		elementData[index] = o;
		size++;
	}
	
	/**
	 * 根据下标获取元素
	 * @param index
	 * @return
	 */
	public Object get(int index) {
		checkRange(index);
		
		return elementData[index];
	}
	
	/**
	 * 删除元素
	 * @param index
	 */
	private void fastRemove(int index) {
		int numMoved = size - index - 1;
		if(numMoved > 0) {
			System.arraycopy(elementData, index + 1, elementData, index, numMoved);
		}
		elementData[--size] = null;
	}
	
	/**
	 * 根据下标删除元素
	 * @param index
	 * @return
	 */
	public Object remove(int index) {
		checkRange(index);
		
		Object oldValue = get(index);
		fastRemove(index);
		
		return oldValue;
	}
	
	/**
	 * 根据元素删除数组中的元素
	 * @param o
	 * @return
	 */
	public boolean remove(Object o) {
		if(o == null) {
			for(int i = 0; i < size; i++) {
				if(elementData[i] == null) {
					fastRemove(i);
					return true;
				}
			}
		}else {
			for(int i = 0; i < size; i++) {
				if(o.equals(elementData[i])) {
					fastRemove(i);
					return true;
				}
			}
		}
		return false;
	}
}