Question

我试图创建一个基于引用的排序列表，但每次我尝试编译它时，都会收到此错误。

＆＃34;缺少退货声明＆＃34;

我真的不明白为什么我会得到它，虽然这似乎是我的locateIndex方法的一个问题

这是我的代码

public class SortedListReferenceBased extends ListReferenceBased
{

    public int index;
    public int numItems;
    public Node head;

    public SortedListReferenceBased()
    // creates an empty list
    {
        numItems = 0;
        head = null;
    }  // end default constructor


    public void add(String item) throws ListException
    // Inserts item into its proper position in a sorted list
    // Throws an exception if the item connot be placed on the list
    {
        try
        {
            locateIndexToAdd(item);
            super.add(index,item);
        }
        catch(Exception e)
        {
            throw new ListException("Add to List failed:  " + e.toString());
        }

    }


    public void remove(String item) throws ListException
    // Removes the item from a sorted list.
    // Throws an exception if the item is not found.
    {
        try
        {
            locateIndexToRemove(item);
            super.remove(index);
            // YOUR CODE WILL BE HERE...
            // REQUIREMENT: USE "locateIndex(String item)" method.
        }
        catch(Exception e)
        {
            throw new ListException("Remove " + item.toString() + " from List failed:  " + e.toString());
        }
    }

    public int locateIndexToAdd(String item)
    // Returns the position where the item belongs or exists in a sorted list;
    // item and the list are unchanged.
    {
        int stop = 0;
        index = 0;
        while (index <= numItems && stop == 0)
        {
            Object curr = super.get(index);
            String current  = curr.toString();
            if (item.compareTo(current) > 0)
                index++;
            else
            {
                stop = 1;
                return index;
            }
        }

    }

    public int locateIndexToRemove(String item)
    // Returns the position where the item belongs or exists in a sorted list;
    // item and the list are unchanged.
    {
        int found = 0;
        index = 0;
        while (index <= numItems && found == 0)
        {
            Object curr = super.get(index);
            String current  = curr.toString();
            if (item.compareTo(current) == 0)
            {
                found = 1;
                return index;
            }
            else
            {
                index ++;
            }
        }
        if (found == 0)
            System.out.println("Item not found");

    }

}  // end SortedListReferenceBased

Answer 1

此方法确实缺少return语句

public int locateIndexToRemove(String item)
// Returns the position where the item belongs or exists in a sorted list;
// item and the list are unchanged.
{
    int found = 0;
    index = 0;
    while (index <= numItems && found == 0)
    {
        Object curr = super.get(index);
        String current  = curr.toString();
        if (item.compareTo(current) == 0)
        {
            found = 1;
            return index;
        }
        else
        {
            return index ++; // or here
        }
    }
    if (found == 0)
        System.out.println("Item not found");

    return index; // <-- the missing return statement.
}

这里有一个：

        if (item.compareTo(current) == 0)
    {
        found = 1;
        return index;
    }

是不够的，因为如果if语句返回false会发生什么，则不再有值返回，因此编译器会抱怨缺少return语句。

Answer 2

WonderWorld回答得对。当你在locateIndexToRemove方法签名中指定你的返回类型必须是int时，你必须返回int。在这个方法中发生的事情是你的locateIndexToRemove的while循环中的if和else语句没有运行，或者你的while本身没有运行，这使得locateIndexToRemove方法无法返回一个int值。

Answer 3

我认为这会为你效劳，

    int stop = 0;
    index = 0;
    while (index < numItems && stop == 0)
    {
        Object curr = super.get(index);
        String current  = curr.toString();
        if (item.compareTo(current) > 0)
            index++;
        else
        {
            stop = 1;
        }
    }
    return index;

我认为你必须增加和减少＆＃34; numItems＆＃34;添加和删除项目时。

缺少返回语句错误（基于参考列表）

3 个答案: