对于ArrayList相比大家都很熟悉，它是java中最常用的集合之一。下面就给出它的自我实现的java代码。
需要说明的一点是，它是基于数组创建的。所以它在内存中是顺序存储，对于查找十分的方便。
package com.pinjia.shop.common.collection; import java.util.Iterator;
import java.util.NoSuchElementException; /**
* Created by wangwei on 2017/1/3.
* ArrayList的自己封装，实现
*/
public class MyArrayList<E> implements Iterable<E> { private static final int DEFAULT_SIZE = 10;//容器默认大小
private int theSize;
private E[] theItems; public MyArrayList(){
clear();
} public void clear(){
theSize = 0;
ensureCapacity(DEFAULT_SIZE);
} public int size(){
return theSize;
} public boolean isEmpty(){
return size() == 0;
} public void trimToSize(){
ensureCapacity(size());
} public E get(int idx){
if(idx<0||idx>=size())
throw new ArrayIndexOutOfBoundsException();
return theItems[idx];
} public E set(int idx,E newVal){
if(idx<0||idx>size())
throw new ArrayIndexOutOfBoundsException();
E old = theItems[idx];
theItems[idx] = newVal;
return old;
} public void ensureCapacity(int newCapacity) { //数组的扩展
if(newCapacity<theSize)
return;
E[] old = theItems;
theItems = (E[])new Object[newCapacity];
for(int i=0;i<size();i++){
theItems[i] = old[i];
}
} public boolean add(E x){
add(size(),x);
return true;
} public void add(int idx,E x){
if(theItems.length == size())
ensureCapacity(size()*2+1);
for(int i=theSize;i>idx;i--){
theItems[i] = theItems[i-1];
}
theItems[idx] = x;
theSize++;
} public E remove(int idx){
E removeItem = theItems[idx];
for(int i=idx;i<size()-1;i++){
theItems[i] = theItems[i+1];
}
theSize--;
return removeItem;
} public Iterator<E> iterator() {
return new ArrayListIterator();
} private class ArrayListIterator implements Iterator<E>{ //内部类
private int current = 0;
public boolean hasNext(){
return current<size();
}
public E next(){
if(!hasNext())
throw new NoSuchElementException();
return theItems[current++];
}
public void remove(){
MyArrayList.this.remove(--current);
}
}
}