顺序表--MyArrayList的实现

实现的MyArrayList实为顺序表结构,其中要实现Iterable时必须在内部实现Iterator,即为该表的迭代器.

  public class MyArrayList<AntType> implements Iterable<AntType> {
     @Override
     public Iterator<AntType> iterator() { //实现接口
         return new MyIterator();
     }
     private class MyIterator implements Iterator<AntType> {

         private int current = 0;

         @Override
         public boolean hasNext() {
             return current < size();
         }

         @Override
         public AntType next() {
             if(!hasNext())
                 throw new NoSuchElementException();
             return theItems[current ++];//迭代器从第一个元素开始迭代,即theItem[0]
         }
         public void remove(){
             MyArrayList.this.remove(--current);
         }
     }

     private static final int DEFAULT_CAPACITY = 10; //设置默认容量

     private int theSize;  //当前大小
     private AntType [] theItems;  //元素对象数组

     public MyArrayList(){ //构造函数，生成空表
         clear();
     }

     public void clear(){ //归为默认(清空)
         theSize = 0;
         ensureCapacity(DEFAULT_CAPACITY);
     }

     public void ensureCapacity(int newCapacity ){ //重置表的容量
         AntType [] oldItems = theItems;
         theItems = (AntType []) new Object[newCapacity];//****重新分配空间 注意使用强制转换的方式进行定义
         for (int i = 0 ; i < theSize; i++){
             theItems[i] = oldItems[i];
         }
     }

     public int size(){ //当前使用大小
         return theSize;
     }

     public boolean isEmpty(){  //判断是否为空
         return theSize == 0;
     }

     public void trimToSize(){  //将表的容量设为当前使用的大小
         ensureCapacity(size());
     }

     public AntType get(int idx){
         //判断是否越界的合法性
         if(idx < 0 || idx >= theSize)
             throw new ArrayIndexOutOfBoundsException();//越界异常
         else
             return theItems[idx];
     }

     //替换元素
     public AntType set(int idx, AntType newVal){
         if( idx < 0 || idx >= theSize)
             throw  new ArrayIndexOutOfBoundsException();
         AntType oldVal = theItems[idx];
         theItems[idx] = newVal;
         return oldVal;
     }

     public boolean add( AntType newVal){//末尾添加元素
         if(theItems.length == size())
             ensureCapacity(size() * 2 + 1);
         set(theSize++ , newVal);
         return true;
     }

     public void add( int idx, AntType newVal){//任意位置添加元素
         if(theItems.length == size())
             ensureCapacity(size() * 2 + 1);
         for(int i = size(); i > idx; i--)
             theItems[i] = theItems[i - 1];
         theItems[idx] = newVal;
         theSize ++;
     }

     public AntType remove(int idx) {
         AntType val = theItems[idx];
         for (int i = idx; i < theSize - 1; i++) {
             theItems[i] = theItems[i + 1];
         }
         theSize--;
         return val;
     }
 }