自己实现 ArrayList

来源：互联网发布：windows启动程序脚本编辑：程序博客网时间：2024/06/05 07:50

英文原文

ArrayList 类似于 Array 对象，但是当列表中的对象数量增加时，它提供了动态空间分配的功能。在 Array 对象中，我们需要在初始化时提供数组的大小，但这并不是 ArrayList 所必需的。实际上，当您初始化ArrayList时，它将自动将其容量分配为10。

这里我用 Array 对象实现ArrayList，并提供 get(index)，add(object) 和 remove(index) 等基本函数。

import java.util.ArrayList;/** * <p></p> * * @author 三产 * @version 1.0 * @date 2017-03-24 * @QQGroup 213732117 * @website http://www.coderknock.com * @copyright Copyright 2017 拿客 coderknock.com  All rights reserved. * @since JDK 1.8 */public class MyArrayList {        private static final int SIZE_FACTOR=5;        private Object data[];        private int index;        private int size;        public MyArrayList(){            this.data=new Object[SIZE_FACTOR];            this.size=SIZE_FACTOR;        }        public void add(Object obj){            System.out.println("index:"+this.index+"size:"+this.size+"data size:"+this.data.length);            if(this.index==this.size-1){                //我们需要加大data[]的大小                increaseSizeAndReallocate();            }            data[this.index]=obj;            this.index++;        }        private void increaseSizeAndReallocate() {            this.size=this.size+SIZE_FACTOR;            Object newData[]=new Object[this.size];            for(int i=0; i<data.length;i++){                newData[i]=data[i];            }            this.data=newData;            System.out.println("***index:"+this.index+"size:"+this.size+"data size:"+this.data.length);        }        public Object get(int i) throws Exception{            if(i>this.index-1){                throw new Exception("ArrayIndexOutOfBound");            }            if(i<0){                throw new Exception("Negative Value");            }            return this.data[i];        }        public void remove(int i) throws Exception{            if(i>this.index-1){                throw new Exception("ArrayIndexOutOfBound");            }            if(i<0){                throw new Exception("Negative Value");            }            System.out.println("Object getting removed:"+this.data[i]);            for(int x=i; x<this.data.length-1;x++){                data[x]=data[x+1];            }            this.index--;        }        public static void main(String[] args) throws Exception {            MyArrayList mal = new MyArrayList();            mal.add("0");            mal.add("1");            mal.add("2");            mal.add("3");            mal.add("4");            mal.add("5");            mal.add("6");            mal.add("7");            mal.add("8");            mal.add("9");            mal.remove(5);            System.out.println(mal.get(7));        }}

输出如下：

index:0size:5data size:5index:1size:5data size:5index:2size:5data size:5index:3size:5data size:5index:4size:5data size:5***index:4size:10data size:10index:5size:10data size:10index:6size:10data size:10index:7size:10data size:10index:8size:10data size:10index:9size:10data size:10***index:9size:15data size:15Object getting removed:58

这只是使用 Array 基本实现 ArrayList 的功能，只为了解其原理。还请使用 JDK 中的 ArrayList。

原文中并为实现泛型，我们就来补充下：

import java.util.ArrayList;/** * <p></p> * * @author 三产 * @version 1.0 * @date 2017-03-24 * @QQGroup 213732117 * @website http://www.coderknock.com * @copyright Copyright 2017 拿客 coderknock.com  All rights reserved. * @since JDK 1.8 */public class MyArrayList<T> {        private static final int SIZE_FACTOR=5;        private Object data[];        private int index;        private int size;        public MyArrayList(){            this.data=new Object[SIZE_FACTOR];            this.size=SIZE_FACTOR;        }        public void add(T obj){            System.out.println("index:"+this.index+"size:"+this.size+"data size:"+this.data.length);            if(this.index==this.size-1){                //我们需要加大data[]的大小                increaseSizeAndReallocate();            }            data[this.index]=obj;            this.index++;        }        private void increaseSizeAndReallocate() {            this.size=this.size+SIZE_FACTOR;            Object newData[]=new Object[this.size];            for(int i=0; i<data.length;i++){                newData[i]=data[i];            }            this.data=newData;            System.out.println("***index:"+this.index+"size:"+this.size+"data size:"+this.data.length);        }        public T get(int i) throws Exception{            if(i>this.index-1){                throw new Exception("ArrayIndexOutOfBound");            }            if(i<0){                throw new Exception("Negative Value");            }            return (T) this.data[i];        }        public void remove(int i) throws Exception{            if(i>this.index-1){                throw new Exception("ArrayIndexOutOfBound");            }            if(i<0){                throw new Exception("Negative Value");            }            System.out.println("Object getting removed:"+this.data[i]);            for(int x=i; x<this.data.length-1;x++){                data[x]=data[x+1];            }            this.index--;        }        public static void main(String[] args) throws Exception {            MyArrayList<Integer> mal = new MyArrayList<Integer>();            mal.add(0);            mal.add(1);            mal.add(2);            mal.add(3);            mal.add(4);            mal.add(5);            mal.add(6);            mal.add(7);            mal.add(8);            mal.add(9);            mal.remove(5);            System.out.println(mal.get(7));        }}

这里其实只是修改了 add(T)、get(index) 方法。

0 0