package code01;
/**
* Created by yaoyuan on 2017/3/6.
*/
public class ArrayList implements List {
private int max_size = 0;//总长度
private int current_size = 0; //当前长度
private float extendPercent = 2; //扩展系数
private Object[] elementData;
/**
* 默认构造函数，初始化数组长度为100
*/
public ArrayList(){
this.elementData = new Object[100];
this.max_size = 100;
}
/**
* 构造函数
* @param size，初始化数组长度
*/
public ArrayList(int size){
this.elementData = new Object[size];
this.max_size = size;
}
/**
* 顺序添加元素，超出原始界限时，数组自动扩展
*/
public void add(Object o) {
//如果越界了，需要复制原有的数组到扩充后的数组中
if(this.current_size + 1 > this.max_size) {
this.max_size = (int) Math.floor(this.max_size * this.extendPercent);
this.elementData = copyToNew(this.elementData,this.max_size);
}
this.elementData[this.current_size] = o;
this.current_size ++;
}
/**
* 指定位置添加元素
* 一种是在中间，一种是当前插入的位置尾部(如果超过尾部则默认添加到尾部)
*/
public void add(int index, Object o){
assert(index>=0);
//如果越界了，需要复制原有的数组到扩充后的数组中
if(this.current_size + 1 > this.max_size) {
//如果越界了，需要复制原有的数组到扩充后的数组中
this.max_size = (int) Math.floor(this.max_size * this.extendPercent);
this.elementData = copyToNew(this.elementData,this.max_size);
}
//数组中间插入
if(index < this.current_size){
//需要把当前位置的元素往后移动
for (int i = this.current_size - 1; i >= index; i--) {
this.elementData[i+1] = this.elementData[i];
}
this.elementData[index] = o;
}else {
//后面加入
this.elementData[this.current_size] = o;
}
this.current_size ++;
}
public Object get(int index){
if(index >= 0 && index <= this.current_size-1){
return this.elementData[index];
}else {
throw new ArrayIndexOutOfBoundsException(index);
}
}
/**
* 删除指定位置的元素
* @param index
* @return
*/
public Object remove(int index){
Object result = null;
if(index >= 0 && index <= current_size-1){
result = elementData[index];
//删除操作
if(index == current_size - 1){
elementData[index] = null;
}else {
//需要把当前位置后面的元素往前移动
for (int i = index; i < this.current_size-1 ; i++) {
this.elementData[i] = this.elementData[i+1];
}
this.elementData[this.current_size-1] = null;
}
this.current_size --;
}else {
throw new ArrayIndexOutOfBoundsException(index);
}
return result;
}
public int size(){
return this.current_size;
}
public Iterator iterator(){
return new Iterator() {
int next_pos = 0;
int pos = -1;
public boolean hasNext() {
if(max_size <= 0){
return false;
}
return next_pos < ArrayList.this.size();
}
public Object next() {
Object next = ArrayList.this.get(next_pos);
pos = next_pos ++;
return next;
}
public void remove(){
ArrayList.this.remove(pos);
}
};
}
private Object[] copyToNew(Object[] oldArray, int extendSize){
Object[] newArray = new Object[extendSize];
for (int i = 0; i < size(); i++) {
newArray[i] = oldArray[i];
}
return newArray;
}
}