一条晕的语句

最新推荐文章于 2021-07-02 09:58:57 发布

原创最新推荐文章于 2021-07-02 09:58:57 发布 · 688 阅读

0 ·

CC 4.0 BY-SA版权

文章标签：

#import #iterator #string #class #null #object

package com.corejava.collec;

import java.util.AbstractQueue;
import java.util.ConcurrentModificationException;
import java.util.Iterator;
import java.util.NoSuchElementException;
import java.util.Queue;

/**
* @author teddy.lu 06-07-18
*/
public class CircularArrayQueueTest {

/**
* @param args
*/
public static void main(String[] args) {

  Queue<String> q = new CircularArrayQueue<String>(10);
  q.add("Amy");
  q.add("Bob");
  q.add("Carl");
  q.add("Deedee");
  q.add("Emile");

q.add("Fifi");

  for (Iterator iter = q.iterator(); iter.hasNext();) {
   String element = (String) iter.next();
   System.out.println(element);
  }
  System.out.println("size :" + q.size());

}

class CircularArrayQueue<E> extends AbstractQueue<E> {

private E[] elements;

private int head;

private int tail;

private int count;

private int modcount;

/**
* constructs an empty queue
*
* @param capacity
*/
public CircularArrayQueue(int capacity) {
  super();
  elements = (E[]) new Object[capacity];
  this.modcount = 0;
  this.count = 0;
  this.head = 0;
  this.tail = 0;
}

@Override
public Iterator<E> iterator() {
return new QueueIterator();
}

@Override
public int size() {

return count;
}

public boolean offer(E o) {
assert elements != null;

// there are still remain space
if (count < elements.length) {

   elements[tail] = o;
   tail = (tail++) % elements.length;
   count++;
   modcount++;
   return true;
  } else {
   return false;

}

public E peek() {
  if (count == 0) {
   return null;
  } else
   return elements[head];
}

public E poll() {
// first judge the elements if empty

  if (count == 0) {
   return null;
  } else {

   E e = elements[head];
   head = (head + 1) % elements.length;
   count--;

   modcount++;
   return e;
  }

}

public CircularArrayQueue() {
super();
}

private class QueueIterator implements Iterator<E> {

private int offset;

private int modcountAtConstruct;

  public QueueIterator() {
          System.out.println("modcount is: "+modcount);
   modcountAtConstruct = modcount;
  }

public boolean hasNext() {

   if (modcount != modcountAtConstruct)
    throw new ConcurrentModificationException();
   return offset < elements.length;
  }

  public E next() {
   if (!hasNext())
    throw new NoSuchElementException();
   E r = elements[(head + offset) % elements.length];
   offset++;
   return r;

}

public void remove() {
throw new UnsupportedOperationException();

}

}
}

今天在看core java 7th中关于collection中的内容，在动手运行上面的程序时，发现只保存了最后一个String,结果审阅代码，发现问题竟然出现在 tail = (tail++) % elements.length;　在此记下，以免以后出现同样的错误。认为这语句其实可以分解成3句来执行(1) tail%elements.length 得　0，(2)　tail= tail+1 得　1，(3)再将1的结果赋给tail得0