java集合数据结构实现

                  自定义集合类和java数据结构底层的实现

      对ArrayList的实现，实际就是动态数组  代码分析package cn.itcast.shujujiegou;

package cn.itcast.shujujiegou;

import java.util.Iterator;


/**
 * Created by likailong on 2016/9/27.
 */
public class MyArrayList<T > implements Iterable<T> {
    private static final int DEFAULT_SIZE=10;
    private int theSize;
    private T [] theItems;
    public MyArrayList(){
        doClear();
    }
    public void clear(){
        doClear();
    }
    private void doClear() {
        theSize=0;
        ensureCapacity(DEFAULT_SIZE);
    }
    public void trimToSize(){
        ensureCapacity(size());
    }
    public T get(int index){
        if(index<0||index>=size())
            throw new IndexOutOfBoundsException("数组脚标越界");
        return theItems[index];
    }
    public T set(int index,T element){
        if(index<0||index>=size())
            throw new IndexOutOfBoundsException("数组脚标越界");
        T old=theItems[index];
        theItems[index]=element;
        return old;
    }
    public boolean add(T element){
        add(size(),element);
        return true;
    }
    public void add(int index,T element){
        if(theItems.length==size())
            ensureCapacity(size()*2+1);
        for(int i=size();i>index;i--){
            theItems[i]=theItems[i-1];
        }
        theItems[index]=element;
        theSize++;
    }
    public T remove(int index){
        T remove=theItems[index];
        for(int i=index;i<size()-1;i++)
            theItems[i]=theItems[i+1];
        theSize--;
        return remove;

    }
    public void ensureCapacity(int newCapacity) {
        if(newCapacity<theSize)
            return ;
        T [] old=theItems;
        theItems=(T[])new Object[newCapacity];
        for(int i=0;i<size();i++)
            theItems[i]=old[i];
    }
    public String toString(){
        StringBuilder s=new StringBuilder();
        s.append("[");
        for(int i=0;i<theSize;i++){
            s.append(","+theItems[i]);
        }
        s.append("]");
        return s.toString();
    }
    public  int size() {
        return theSize;
    }
   public boolean isEmpty(){
       return size()==0;
   }
    @Override
    public Iterator<T> iterator() {
        return new ArrayListLiterator();
    }
    private class ArrayListLiterator implements Iterator<T>{
       private int current=0;
        @Override
        public boolean hasNext() {
            return current<size();
        }

        @Override
        public T next() {
            return theItems[current++];
        }
        public void remove(){
            MyArrayList.this.remove(--current);
        }
    }
}