Java手工实现ArrayList

public class WhArrayList<E> {

	private Object[] elementData;
	private int size;
	private static final int DEFAUT_CAPACITY = 10;

	public WhArrayList() {
		elementData = new Object[DEFAUT_CAPACITY];
	}

	public WhArrayList(int capacity) {
		if (capacity < 0) {
			throw new RuntimeException("容量不可为负数！" + capacity);
		} else if (capacity == 0) {
			elementData = new Object[DEFAUT_CAPACITY];
		} else if (capacity > 0) {
			elementData = new Object[capacity];
		}
	}

	public void add(E element) {
		// 数组扩容
		if (size == elementData.length) {
			// 增大1/2 注意这里+号优先级更高，如果不加括号，会变为（10+10）/2，长度依然是10
			Object[] newArray = new Object[elementData.length + (elementData.length >> 1)];
			System.arraycopy(elementData, 0, newArray, 0, elementData.length);
			// 指向新的数组对象
			elementData = newArray;
		}
		elementData[size++] = element;
	}

	// 增加set和get方法
	@SuppressWarnings("unchecked")
	public E get(int index) {
		checkRank(index);
		return (E) elementData[index];
	}

	public void set(E element, int index) {
		checkRank(index);
		elementData[index] = element;
	}

	// 增加remove方法
	public void remove(int index) {
		checkRank(index);
		int numMoved = elementData.length - index - 1;
		if (numMoved > 0) {
			System.arraycopy(elementData, index + 1, elementData, index, numMoved);
		}
		elementData[size - 1] = null;
		size--;
	}

	public void remove(E element) {
		// 挨个对比，获得第一个比较为true的
		for (int i = 0; i < size; i++) {
			if (element.equals(get(i))) {
				remove(i);
			}
		}
	}

	// 判断索引是否合法，多处使用，形成公共方法
	public void checkRank(int index) {
		// 判断索引是否合法
		if (index < 0 || index > size - 1) {
			throw new RuntimeException("索引不合法：" + index);
		}
	}

	public int size() {
		return size;
	}

	public boolean isEmpty() {
		return size == 0;

	}

	@Override
	public String toString() {
		// 重写打印
		StringBuilder sBuilder = new StringBuilder();
		sBuilder.append("[");
		for (int i = 0; i < size; i++) {
			sBuilder.append(elementData[i] + ",");
		}
		sBuilder.setCharAt(sBuilder.length() - 1, ']');
		return sBuilder.toString();
	}

	// 测试功能
	public static void main(String[] args) {
		WhArrayList<String> list1 = new WhArrayList<String>();
		for (int i = 0; i <= 8; i++) {
			list1.add("string" + i);
		}
		System.out.println(list1);

		System.out.println(list1.get(6));
		list1.set("hahahah", 6);
		System.out.println(list1.get(6));
		// list1.set("不合法的位置", 30);

		System.out.println(list1);
		list1.remove(2);
		list1.remove("string4");
		System.out.println(list1);
		
		System.out.println(list1.size);
		System.out.println(list1.isEmpty());
	}
}