15 内部类和ArrayList的实现

关于内部类：

写在内部就是私有的，内部类还是public纯属设计有问题，既然public了为嘛还要塞入内部,内部类一定要是public的话，初始化要依赖外部类的引用，不然类定义里面隐含的Outer.this无法实例化

Outer访问Inner： 一定要创建inner的对象（不然实例化的时候很明显有问题），要么就都是static；Inner在Outer中实例化以后，可以直接Inner的私有属性，这个是强制规定，当然有点破坏了automic unit的规定，嵌套类也是如此

Inner访问Outer：默认有个Outer.this引用,当然Outer的属性和方法在Inner内可以直接访问，不需加Outer.this区分（名字没有二义性的时候，不然会被覆盖）

关于ArrayList的设计：

迭代器remove()更好，当然这个方法过于依赖其他方法的实现，耦合很大，比如内部的字段expectedModCount因为要知道ArrayList的modCount会修改才修改。

ConcurrentModificationException通过字段modCount实现，当然没有同步，所以并发的时候还是会有错不提示，只是一个思路罢了。

代码：

package nuaa.ds;import java.util.AbstractCollection;import java.util.Collection;import java.util.ConcurrentModificationException;import java.util.Iterator;import java.util.List;import java.util.ListIterator;import java.util.NoSuchElementException;public class ArrayList<T> extends AbstractCollection<T> implements List<T> {private static final int DEFAULT_CAPACITY = 2;private static final int NOT_FOUND = -1;private T[] theItems;private int theSize;private int modCount = 0;//保存对对象的修改次数，目的是保持迭代器和集合类的一致性public ArrayList(){clear();}public ArrayList(Collection<? extends T> c){clear();for(T obj:c)add(obj);}@Overridepublic void clear() {theSize = 0;theItems = (T[])new Object[this.DEFAULT_CAPACITY];modCount++;}@Overridepublic boolean addAll(int index, Collection<? extends T> c) {// TODO Auto-generated method stubreturn false;}@Overridepublic T get(int index) {if(index<0||index>=size())throw new ArrayIndexOutOfBoundsException();return theItems[index];}@Overridepublic T set(int index, T element) {if(index<0||index>size())throw new ArrayIndexOutOfBoundsException();T old = theItems[index];theItems[index] = element;return old;}@Overridepublic boolean contains(Object o) {return findPos(o)!=NOT_FOUND;}private int findPos(Object o){for(int i=0;i<size();i++){if(o==null){if(theItems[i]==null)return i;}else if(o.equals(theItems[i])){return i;}}return this.NOT_FOUND;}@SuppressWarnings("unchecked")@Overridepublic boolean add(T e) {if(theItems.length==size()){T[] old = theItems;theItems = (T[])new Object[theItems.length*2+1];for(int i=0;i<size();i++)theItems[i] = old[i];}theItems[theSize++] = e;modCount++;return true;}@Overridepublic void add(int index, T element) {}@Overridepublic T remove(int index) {T removedItem = theItems[index];for(int i=index;i<size()-1;i++)theItems[i] = theItems[i+1];theSize--;modCount++;return removedItem;}@Overridepublic boolean remove(Object o) {int pos = findPos(o);if(pos==this.NOT_FOUND)return false;else{remove(pos);return true;}}@Overridepublic int indexOf(Object o) {// TODO Auto-generated method stubreturn 0;}@Overridepublic int lastIndexOf(Object o) {// TODO Auto-generated method stubreturn 0;}@Overridepublic ListIterator<T> listIterator() {// TODO Auto-generated method stubreturn null;}@Overridepublic ListIterator<T> listIterator(int index) {return new ArrayListIterator(index);}@Overridepublic List<T> subList(int fromIndex, int toIndex) {// TODO Auto-generated method stubreturn null;}@Overridepublic Iterator<T> iterator() {return new ArrayListIterator(0);}@Overridepublic int size() {return theSize;}private class ArrayListIterator implements ListIterator<T>{private int current;private int expectedModCount = modCount;private boolean nextCompleted = false;private boolean prevCompleted = false;ArrayListIterator(int pos){if(pos<0||pos>size())throw new IndexOutOfBoundsException();current = pos;}@Overridepublic boolean hasNext() {if(expectedModCount!=modCount)throw new ConcurrentModificationException();return current<size();}@Overridepublic T next() {if(!hasNext())throw new NoSuchElementException();nextCompleted = true;prevCompleted = false;return theItems[current++];}@Overridepublic boolean hasPrevious() {if(expectedModCount!=modCount)throw new ConcurrentModificationException();return current>0;}@Overridepublic T previous() {if(!hasPrevious()){throw new NoSuchElementException();}prevCompleted = true;nextCompleted = false;return theItems[--current];}@Overridepublic int nextIndex() {// TODO Auto-generated method stubreturn 0;}@Overridepublic int previousIndex() {// TODO Auto-generated method stubreturn 0;}@Override/** * 迭代器的remove因为已经有了current， * 因此删除的时候很明显比类原始的remove（obj）方法少一个阶的复杂度 */public void remove() {if(expectedModCount!=modCount)throw new ConcurrentModificationException();if(nextCompleted)ArrayList.this.remove(--current);//调用next的时候current已经指向下一项else if(prevCompleted)ArrayList.this.remove(current);elsethrow new IllegalStateException();prevCompleted = nextCompleted = false;expectedModCount++;//调用容器的remove方法属性modCount会自增}@Overridepublic void set(T e) {// TODO Auto-generated method stub}@Overridepublic void add(T e) {// TODO Auto-generated method stub}}//cheap mainpublic static void main(String[] args){ArrayList<Integer> al = new ArrayList<Integer>();for(int i=0;i<20;i++){al.add(i);}System.out.print(al.toString());}}