数据结构与算法系列之＜3＞----动态数组(Part2)

1、动态数组–泛型

• 接着上一篇，现在不仅可以存放int类型，也可以存放对象类型的元素了

package com.jh;

import java.util.Iterator;

@SuppressWarnings("unchecked")
public class ArrayList<E> {
	/**
	 *  多少个元素
	 */
	private int size;
	
	/**
	 * 存放元素
	 */
	private E[] elements;
	
	private static final int DEFAULT_CAPACITY = 10;
	private static final int ELEMENT_NOT_FOUND = -1;
	
	public ArrayList(int capacity) {
		capacity = (capacity < DEFAULT_CAPACITY) ? DEFAULT_CAPACITY : capacity;
		elements = (E[]) new Object[capacity];
	}
	
	public ArrayList() {
		this(DEFAULT_CAPACITY);
	}
	/**
	 * 清除所有元素
	 */
	public void clear() {
		size = 0;
	}
	
	/**
	 * 元素的数量
	 * @return
	 */
	public int size() {
		return size;
	}
	
	/**
	 * 是否为空
	 * @return
	 */
	public boolean isEmpty() {
		return size == 0;
	}
	
	/**
	 * 是否包含某个元素
	 * @param element
	 * @return
	 */
	public boolean contains(E element) {
		return indexOf(element) != ELEMENT_NOT_FOUND;
	}

	/**
	 * 添加元素到尾部
	 * @param element
	 */
	public void add(E element) {
//		elements[size++] = element;
		add(size, element);
	}
	
	/**
	 * 返回某个元素的索引
	 * @param index
	 * @return
	 */
	public E get(int index) {
		rangeCheck(index,false);
		
		return elements[index];
	}
	
	/**
	 * 设置位置的元素
	 * @param index
	 * @param element
	 * @return 原来的元素
	 */
	public E set(int index, E element) {
		rangeCheck(index,false);
		
		E old = elements[index];
		elements[index] = element;
		return old;
	}
	
	/**
	 * 在某个位置插入元素
	 * @param index
	 * @param element
	 */
	public void add(int index, E element) {
		rangeCheck(index,true);
		
		ensureCapacity(size + 1);
		for (int i = size - 1; i >= index; i--) {
			elements[i + 1] = elements[i];
		}
		elements[index] = element;
		size++;
	}
	
	
	/**
	 * 删除某个元素
	 * @param index
	 * @return
	 */
	public E remove(int index) {
		rangeCheck(index,false);
		
		E deleteElement = elements[index];
		for (int i = index + 1; i < size; i++) {
			elements[i - 1] = elements[i];
		}
		size--;
		return deleteElement;
	}
	
	/**
	 * 查看元素的索引
	 * @param element
	 * @return
	 */
	public int indexOf(E element) {
		for (int i = 0; i < size; i++) {
			if (elements[i] == element) return i;
			
		}
		return ELEMENT_NOT_FOUND;
	}
	
	@Override
	public String toString() {
		StringBuilder string = new StringBuilder();
		string.append("size ==").append(size).append(", [");
		for (int i = 0; i < size; i++) {
			string.append(elements[i]);
			
			if (i != size -1) {
				string.append(",");
			}
		}
		string.append("]");
		return string.toString();
	}
	
	
	private void rangeCheck(int index, boolean isForAdd) {
		if (index < 0 || (isForAdd ? (index > size) : (index >= size))) {
			throw new IndexOutOfBoundsException("Index:" + index + ", size:" + size);
		}
	}
	
	/**
	 * 保证容量
	 * @param capacity
	 */
	private void ensureCapacity(int capacity) {
		int oldCapacity = elements.length;
		System.out.println("oldCapacity:" + oldCapacity + "_" + "capacity:" + capacity);
		if (oldCapacity >= capacity) {
			return;
		}
		
		int newCapacity = oldCapacity + (oldCapacity >> 1);
		E[] newElements = (E[]) new Object[newCapacity];
		for (int i = 0; i < size; i++) {
			newElements[i] = elements[i];
		}
		elements = newElements;
		System.out.println("扩容了" + oldCapacity + "新容量：" + newCapacity);
	}
}