台哥算法练习 自己写的一个ArrayList

眼过千遍，不如手过一遍。亲身下河知深浅，亲口尝梨知酸甜。 

package suanfa;

/**
 * 当年学习数据结构和算法的时候，自己写的一个ArrayList 
 * 可以看到，ArrayList是以数组为基础建立起来的，在容量不够时，需要动态扩展它的容量。
 * 
 * 这里推荐一本学习数据结构和算法的书籍，《数据结构java版》清华大学出版社，译者梁志敏
 * 
 * @author 台哥编程课堂
 * https://blog.csdn.net/chaohi
 * 
 * @param <T>
 */
public class ArrayList<T> {

	private T[] listArr;
	private int listSize;

	// 构造方法
	public ArrayList() {
		listArr = (T[]) new Object[10];
		listSize = 0;
	}

	/**
	 * 设置更大的容量
	 * 
	 * @param minCapacity
	 */
	public void ensureCapacity(int minCapacity) {

		// get the current capacity
		int currentCapacity = listArr.length;

		// only take action if the requested capacity is larger than the
		// existing capacity
		if (minCapacity > currentCapacity) {
			T[] t = (T[]) new Object[minCapacity];
			for (int i = 0; i <= listSize - 1; i++) {
				t[i] = listArr[i];
			}
			listArr = t;
		}
	}

	/**
	 * 把列表容量调整为它的当前大小
	 */
	public void trimToSize() {

		// get the current capacity
		int currentCapacity = listArr.length;

		// only take action if the current capacity is larger than listSize
		if (currentCapacity > listSize) {
			T[] t = (T[]) new Object[listSize];
			for (int i = 0; i <= listSize - 1; i++) {
				t[i] = listArr[i];
			}
			listArr = t;
		}
	}

	/**
	 * 验证index是否位于正确的范围内
	 */
	private void rangecheck(int index, String msg, int upperBound) {
		if (index < 0 || index > upperBound) {
			throw new IndexOutOfBoundsException("/n" + msg + ": index " + index
					+ " out of bounds.Should be in the range 0 to "
					+ upperBound);
		}
	}

	/**
	 * 在索引index处添加元素
	 */
	public void add(int index, T element) {

		// index==listSize is valid; append to the list
		this.rangecheck(index, "ArrayList add()", listSize);

		// see if we need to reallocate more memory
		if (listSize == listArr.length) {
			this.ensureCapacity(2 * listArr.length);
		}

		// shift elements at positions index through listSize-1 to the right
		for (int i = listSize - 1; i >= index; i--) {
			listArr[i + 1] = listArr[i];
		}

		// insert element at location index and increment the list size
		listArr[index] = element;
		listSize++;
	}

	/**
	 * 在尾部添加元素并返回true
	 */
	public boolean add(T element) {
		this.add(listSize, element);
		return true;
	}

	/**
	 * 返回第一个element元素的索引
	 */
	public int indexOf(T element) {
		for (int i = 0; i <= listSize - 1; i++) {
			if (listArr[i].equals(element))
				return i;
		}
		return -1;
	}

	/**
	 * 返回最后一个element元素的索引
	 */
	public int lastIndexOf(T element) {
		for (int i = listSize - 1; i >= 0; i--) {
			if (listArr[i].equals(element))
				return i;
		}
		return -1;
	}

	/**
	 * 删除索引index处的元素
	 */
	public T remove(int index) {

		// verify that index is in the proper range
		this.rangecheck(index, "ArrayList remove()", listSize - 1);

		// save the return value
		T returnElement = listArr[index];

		// shift elements at indices index+1 to listSize-1 left one position
		for (int i = index; i < listSize - 1; i++) {
			listArr[i] = listArr[i + 1];
		}

		// make former last entry a null reference and decrement list size
		listArr[listSize - 1] = null;
		listSize--;

		// return the value that was removed
		return returnElement;
	}

	/**
	 * 删除列表中的element元素
	 */
	public boolean remove(T element) {
		int index = this.indexOf(element);
		if (index != -1) {
			this.remove(index);
			return true;
		}
		return false;
	}

	/**
	 * 得到索引index处的元素
	 */
	public T get(int index) {
		// verify that index is in the proper range
		this.rangecheck(index, "ArrayList get()", listSize - 1);
		return listArr[index];
	}

	/**
	 * 为索引index处的元素赋值
	 */
	public T set(int index, T element) {

		// verify that index is in the proper range
		this.rangecheck(index, "ArrayList set()", listSize - 1);

		// save the element at listArr[index]
		T previousValue = listArr[index];

		// assign the element at index index
		listArr[index] = element;

		// return the previous element
		return previousValue;
	}

	/**
	 * 返回列表的长度
	 */
	public int size() {
		return listSize;
	}

	/**
	 * 判断列表是否为空
	 */
	public boolean isEmpty() {
		return listSize == 0;
	}

	/**
	 * 清空列表
	 */
	public void clear() {
		for (int i = 0; i < listSize; i++) {
			listArr[i] = null;
		}
		listSize = 0;
	}

	/**
	 * 判断列表中是否存在元素element
	 */
	public boolean contains(T element) {
		return !(this.indexOf(element) == -1);
	}

	/**
	 * 返回对应的数组
	 */
	public T[] toArray() {
		T[] t = (T[]) new Object[listSize];
		for (int i = 0; i < listSize; i++) {
			t[i] = listArr[i];
		}
		return t;
	}

}