我在迭代器读取3个以上项目时遇到问题

时间:2018-09-28 05:08:27

标签: java database algorithm iterator

因此,在过去的几个小时中,我查看了此代码,但未找到错误。子集接收一个由3个String字符组成的数组,它将仔细读取并打印出来,但是,如果我添加了三个以上的元素,它将抛出arrayoutofbounds异常,我无法弄清楚原因。我可以一一手动添加它们,它可以工作,但是那不是程序设计工作的方式。我确定解决方案很简单,但我找不到它。有任何想法吗?非常感谢。

package a02;

import java.util.Iterator;

import edu.princeton.cs.algs4.StdRandom;


/**
 * 
 * @author Danny
 *
 * @param <Item>
 */
public class RandomizedQueue<Item> implements Iterable<Item> {
private Item[] queue  ;
private int size;
/**
 * Constructs an empty randomized queue.
 */
public RandomizedQueue() {
    queue = (Item[])new Object[1];
    size=0;
}
/**
 * parameterized constructor for the Iterator class.
 * @param array
 */
private RandomizedQueue(Item[] array)
{
    int count = 0;
    queue = array;
    while(queue[count]!=null)
        count++;
    queue = (Item[])new Object[array.length];
    for(int i=0;i<count;i++)
        queue[i]=array[i];
    size=count;
}

private Item[] getArray() {
    return queue;
}

/**
 * Checks to see if the queue is empty.
 * @return
 */
public boolean isEmpty() {                
    return size<=0;
}

/**
 * Returns the number of items in the queue.
 * @return
 */
public int size() {                  
    return size;
}

/**
 * Adds an item.
 * @param item
 */
public void enqueue(Item item) {    
     if (item == null) 
         throw new java.lang.NullPointerException();
    if (size == queue.length)
        resize(2*queue.length);
    queue[size]= item;
    size++;
}

/**
 * Deletes and returns a random item
 * @return
 */
public Item dequeue() {      
    if (isEmpty())
        throw new java.util.NoSuchElementException();
    int index = StdRandom.uniform(size);
    Item item = queue[index];
    if(index == size-1)
        queue[index] = null;
    else {
        queue[index] = queue[size-1];
        queue[size-1]=null;
    }
    size--;
    if(size<=queue.length/4)
        resize(queue.length/2);
    return item;
}

/**
 * Returns a random item, but does not delete it.
 * @return
 */
public Item sample() {
    if (isEmpty())
        throw new java.util.NoSuchElementException();
    int index = StdRandom.uniform(size);
    return queue[index];
}

/**
 * Returns an independent iterator over items in  random order.
 */
public Iterator<Item> iterator(){     
    return new RandomizedQueueIterator();
}

/**
 * 
 * @author Danny
 *
 */
private class RandomizedQueueIterator implements Iterator<Item>{
    RandomizedQueue<Item> rq = new RandomizedQueue<>(queue);
    @Override
    public boolean hasNext() {          
        return rq.size()!=0;
    }

    @Override
    public Item next() {    
        return rq.dequeue();
    }

    @Override
    public void remove() { 
        throw new java.lang.UnsupportedOperationException();
    }


}

/**
 * Resizes the queue array by the given size.
 * @param d
 */
private void resize(int d) {
    Item[] newArray = (Item[]) new Object[d];
    for(int i = 0;i<size;i++)
        newArray[i]=queue[i];
    queue = newArray;
}

/**
 * Unit Testing
 * @param args
 */
public static void main(String[] args) {
    RandomizedQueue<Integer> rq = new RandomizedQueue<>();
    rq.enqueue(1);
    rq.enqueue(2);
    rq.enqueue(3);
    rq.enqueue(4);
    rq.enqueue(5);
    rq.enqueue(6);
    rq.enqueue(7);

    Iterator<Integer> iterator1 = rq.iterator();
    while(iterator1.hasNext())
        System.out.println(iterator1.next());

    System.out.println();

    Iterator<Integer> iterator2 = rq.iterator();
    while(iterator2.hasNext())
        System.out.println(iterator2.next());

}
}


package a02;

import java.util.Iterator;

 public class Subset {

public static void main(String[] args) {
    //char [] c = {'b', 'a', 'C'};
    String[] c= {"hello", "hi", "howdy", "english"};
        RandomizedQueue<String> queue = new RandomizedQueue<String>();
        for (int i=0;i<c.length; i++)
            queue.enqueue(c[i]);
        int k=3;
        Iterator<String> iterator=queue.iterator();
        for (int i=0; i<k;i++) {
            System.out.println(iterator.next());
        }
}

}

1 个答案:

答案 0 :(得分:0)

在构造器RandomizedQueue(Item[] array)中,您需要在访问queue之前添加边界检查。

更改:

while(queue[count]!=null)

while(count < queue.length && queue[count]!=null)