顺序表--MyArrayList的实现

  1  public class MyArrayList<AntType> implements Iterable<AntType> {
  2     @Override
  3     public Iterator<AntType> iterator() { //实现接口
  4         return new MyIterator();
  5     }
  6     private class MyIterator implements Iterator<AntType> {
  7 
  8         private int current = 0;
  9 
 10         @Override
 11         public boolean hasNext() {
 12             return current < size();
 13         }
 14 
 15         @Override
 16         public AntType next() {
 17             if(!hasNext())
 18                 throw new NoSuchElementException();
 19             return theItems[current ++];//迭代器从第一个元素开始迭代,即theItem[0]
 20         }
 21         public void remove(){
 22             MyArrayList.this.remove(--current);
 23         }
 24     }
 25 
 26     private static final int DEFAULT_CAPACITY = 10; //设置默认容量
 27 
 28     private int theSize;  //当前大小
 29     private AntType [] theItems;  //元素对象数组
 30 
 31     public MyArrayList(){ //构造函数，生成空表
 32         clear();
 33     }
 34 
 35     public void clear(){ //归为默认(清空)
 36         theSize = 0;
 37         ensureCapacity(DEFAULT_CAPACITY);
 38     }
 39 
 40     public void ensureCapacity(int newCapacity ){ //重置表的容量
 41         AntType [] oldItems = theItems;
 42         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
 43         for (int i = 0 ; i < theSize; i++){
 44             theItems[i] = oldItems[i];
 45         }
 46     }
 47 
 48     public int size(){ //当前使用大小
 49         return theSize;
 50     }
 51 
 52     public boolean isEmpty(){  //判断是否为空
 53         return theSize == 0;
 54     }
 55 
 56     public void trimToSize(){  //将表的容量设为当前使用的大小
 57         ensureCapacity(size());
 58     }
 59 
 60     public AntType get(int idx){
 61         //判断是否越界的合法性
 62         if(idx < 0 || idx >= theSize)
 63             throw new ArrayIndexOutOfBoundsException();//越界异常
 64         else
 65             return theItems[idx];
 66     }
 67 
 68     //替换元素
 69     public AntType set(int idx, AntType newVal){
 70         if( idx < 0 || idx >= theSize)
 71             throw  new ArrayIndexOutOfBoundsException();
 72         AntType oldVal = theItems[idx];
 73         theItems[idx] = newVal;
 74         return oldVal;
 75     }
 76 
 77     public boolean add( AntType newVal){//末尾添加元素
 78         if(theItems.length == size())
 79             ensureCapacity(size() * 2 + 1);
 80         set(theSize++ , newVal);
 81         return true;
 82     }
 83 
 84     public void add( int idx, AntType newVal){//任意位置添加元素
 85         if(theItems.length == size())
 86             ensureCapacity(size() * 2 + 1);
 87         for(int i = size(); i > idx; i--)
 88             theItems[i] = theItems[i - 1];
 89         theItems[idx] = newVal;
 90         theSize ++;
 91     }
 92 
 93     public AntType remove(int idx) {
 94         AntType val = theItems[idx];
 95         for (int i = idx; i < theSize - 1; i++) {
 96             theItems[i] = theItems[i + 1];
 97         }
 98         theSize--;
 99         return val;
100     }
101 }