为队列创建toString

Question

我正在尝试为一个queue类创建一个toString方法，该类以数组格式返回队列的字符串，队列中的最后一个值是字符串中的第一个值。例如，如果按此顺序将1,2,3,4,5添加到队列中，则toString方法将返回5,4,3,2,1。

我尝试过这样做，但似乎无法获得要打印的最后一个值。

下面是我目前使用的toString方法

    public String toString( ) {
    if ( isEmpty() ) {
        return "[]";
    } else {

        String build = "";

        Node current = first;
        while ( current.getNext() != null ) {
            build = current.getElement() + ", " + build;
            current = current.getNext();
        }

        return "[" + build + "]";
    }
}

}

当我按如下方式进行测试时：

public class test {

public static void main( String[] args ){

    Queue q = new Queue(5);

    try {
        q.enqueue(1);
        q.enqueue(2);
        q.enqueue(3);
        q.enqueue(4);
        q.enqueue(5);

        System.out.println(q.toString());

    } catch (QueueFullException e ) {
        e.printStackTrace();
    }
}

}

我一直在想：

[4, 3, 2, 1, ]

任何帮助都是非常感谢的。谢谢

Answer 1

这种方法是可行的：

@Override
public String toString ()
{
    String build = "";

    // I didn't want to make an assumption here - I don't know your implementation
    // If first is null when the queue is empty, then simplify this line
    Node current = (isEmpty()) ? null : first;

    while ( current != null )
    {
        String currElem = String.valueOf(current.getElement());

        // don't add the comma after the first element
        build = (build.length() == 0) ? currElem : currElem + ", " + build;

        current = current.getNext();
    }

    return "[" + build + "]";
}

注意：您不需要空队列的特殊情况-因为构建字符串将为空。

Answer 2

请尝试执行以下操作

while ( current.getNext() != null ) {
             build = current.getElement() + ", " + build;
              current = current.getNext();
         } 
build = current.getElement() + build; // get the value of the last element

因为在最后一个元素中没有next，但应该打印最后一个值

Answer 3

您正在使用current.getNext()检查遍历队列元素。您可以使用

public String toString( ) {
if ( isEmpty() ) {
    return "[]";
} else {

    String build = "";

    Node current = first;
    while ( current != null ) {
        build = current.getElement() + ", " + build;
        current = current.getNext();
    }

    return "[" + build + "]";
}

这将解决您的问题。谢谢。