自定义数组列表和队列

　　最近一直在研究数据结构与算法，涉及到自定义数组和队列，感觉对JDK源代码的底层功能实现学习有一定的帮助，故作此总结，以供参考。

　　ps:JDK的源代码更加复杂，我的自定义数组列表和队列只是一些简单的逻辑实现。

1.自定义数组列表(MyArrayList.java)

package com.BlueStarWei.arrayList;/** *  * show all fields and method,please click "ctrl + o" *  *  * 开发过程遇到的问题： * 1. 传入下标（index）未考虑越界情况 *             一定要校验指针是否越界 * 2. 当容量耗尽后，如何拓展新的空间 *         添加一个变量（hasInitCapacity），用于判断数组的创建方式。 *         如果是通过无参构造方式创建（hasInitCapacity = false），每次扩展容量的时候在原有数组长度的基础上增加拓展长度。 *  * @author HuWei * * @param <E> */public class MyArrayList<E> {    /**     * The default capacity while use constructor form superClass     */    private final int DEFUALT_CAPACITY = 10;        /**     * The expending capacity while arr that is generated via constructor form superClass is full      */    private final int ADD_CAPACITY = DEFUALT_CAPACITY / 2;        /**     * The array to store elements     */    private E[] arr;        /**     * The length of element to be stored into arr     */    private int size;        /**     * check whether is the queue generated by constructor with initCapacity     */    private boolean hasInitCapacity;        public MyArrayList() {        arr = (E[]) new Object[DEFUALT_CAPACITY];        hasInitCapacity = false;    }        public MyArrayList(int initCapacity){        arr = (E[]) new Object[initCapacity];        hasInitCapacity = true;    }        /**     *      * @return     *         the length of array     */    public int size() {        return size;    }    /**     * let element insert to arr     * if MyArrayList is generated via constructor form superClass and the capacity is full,then expand capacity     * @param element        *         the element to insert     * @return index         *         the index of the element to insert     */    public int add(E element){        //expend capacity        if(!hasInitCapacity && size == arr.length){            E[] arr2 = arr;            arr = (E[]) new Object[arr.length + ADD_CAPACITY];            for (int i = 0; i < arr2.length; i++) {                arr[i] = arr2[i];            }        }        arr[size] = element;        return size++;    }        /**     *      * @param index     *         the index of the element to replace     * @param element         *         the element to replace     * @return     *         the element to be replaced     */    public E update(int index, E element){        checkArange(index);        E old = arr[index];        arr[index] = element;        return old;    }        /**     *      * @param index     *         the index of the element to be removed     * @return     *         the element to be removed     */    public E remove(int index){        checkArange(index);                E element = arr[index];        if(index == size - 1){            arr[index] = null;        }        for (int i = index; i < size; i++) {            arr[i] = arr[i+1];        }        size--;        return element;    }        /**     *      * @param index     *         the index of the element to get     * @return     *         the element to get     */    public E get(int index){        return arr[index];    }        /**     * check whether index is out of bounds     * @param index     */    private void checkArange(int index){        if(index < 0 || index >= size){            throw new ArrayIndexOutOfBoundsException();        }    }        @Override    public String toString() {        StringBuilder result = new StringBuilder();        result.append("[");        for (int i = 0; i < size; i++) {            result.append(arr[i]);            if(i != size - 1){                result.append(",");            }        }        result.append("]");        return result.toString();            }    }

 

2. 自定义队列（MyQueue.java）

package com.BlueStarWei.queue;/** * 开发终于到的问题： * 1. 元素poll完（元素实际上并没有从数组中删除，只是将头指针向后移）之后，再次添加数据的时候如何从头开始？ *         判断queue有效的元素是否为空，如果为空，将头指针和尾指针重置到数组最前端 *  * 优化： * 1. 与自定义数组列表相比，在创建队列的时候没有队列的类型为任意集合（E）类型，而是指定为Object[]类型， *         只有在元素返回时，返回为任意集合（E）类型 *          * @author HuWei * * @param <E> */public class MyQueue<E> {        /**     * The default capacity while use constructor form superClass     */    private final int DEFUALT_CAPACITY = 10;        /**     * The expending capacity while arr that is generated via constructor form superClass is full      */    private final int ADD_CAPACITY = DEFUALT_CAPACITY / 2;        /**     * store the element     */    private Object[] queue;        /**     * the head pointer of queue     *it always point the first alive element     */    private int front;        /**     * the end pointer of queue     * it always point the last alive element     */    private int end;        /**     * the real size of queue     */    private int size;        /**     * check whether is the queue generated by constructor with initCapacity     */    private boolean hasInitCapacity;        /**     * generate a queue whose default size is DEFUALT_CAPACITY     */    public MyQueue() {        queue = new Object[DEFUALT_CAPACITY];        hasInitCapacity = false;        end = -1;    }        /**     * generate a queue whose default size is initCapacity     */    public MyQueue(int initCapacity){        queue = new Object[initCapacity];        hasInitCapacity = true;        end = -1;    }        /**     * store element to queue     * @param element     *         the element to be stored     */    public void push(E element){        if(!hasInitCapacity && size == queue.length){            Object[] queue2 = queue;            queue = new Object[size + ADD_CAPACITY];            for (int i = 0; i < queue2.length; i++) {                queue[i] = queue2[i];            }        }        queue[++end] = element;        size++;    }        /**     * remove the first alive element in queue     * while queue is queue is empty, set front and end pointer point the queue's head      *      * @return     *         the element to be remove     */    public E poll(){        E element = (E)queue[front++];        size--;        if(isEmpty()){            front = 0;            end = -1;        }        return element;    }        /**     * get the first alive element in queue     * @return     *         the element to be returned     */    public E peek(){        E element = (E)queue[front];        if(isEmpty()){            element = null;        }        return element;    }        /**     * check whether is queue empty.     *      * @return     *      */    public boolean isEmpty(){        if(size == 0){            return true;        }else {            return false;        }    }        /**     * get the size of queue     *      * @return     *         the size of queue     */    public int size(){        return size;    }}

 

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