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;
    }
}