使用ListIterator从要连接的列表的末尾开始

Question

So what I am trying to do is take the list I have and start at the end. From there I need to go backwards and return the list as a String. So my array has "Words are flowing out like endless rain into a paper cup". I'm trying to make them cuppaperainto... and so on. This is my code but it is giving me a symbol not found error on my list.size and list.listIterator. Just wondering what I'm doing wrong and how to fix this problem.

public class LabListIterators {

public static void main(String[] args) {

    List<String> list = new LinkedList<String>();

    // Add items to the List
      String [] array = {"Words", "are", "flowing", "out", "like", "endless", "rain", "into", "a", "paper", "cup"};
      for (int i = 0; i < array.length; ++i)
            list.add (array[i]);
    System.out.println(list + ", size = " + list.size());
    capitalize(list);
    System.out.println(list);
    System.out.println(concatenateBackwards(list));      
}
public static String concatenateBackwards(List<String> words)
 {
  ListIterator iter = list.listIterator(list.size());
  while (iter.hasPrevious())
  {
     String str = iter.previous() + str; 
  }
  return str;  
 }
}

Answer 1

You just got the names and the scope mixed up a little from this code block

public static String concatenateBackwards(List<String> words)
{
   ListIterator iter = list.listIterator(list.size());
   while (iter.hasPrevious())
  {
     String str = iter.previous() + str; 
  }
  return str;  
}

1. The method takes in List<String> words but you are trying to call listIterator() on a object list which I think you wanted to use when you created within the main() method.

2. Inside the while loop:

    String str = iter.previous() + str; 

   You have to declare str first before you can use it. So move the str declaration before the while loop. Also, the return str; does not know about the scope of tr because it is declared within the while loop body.

Solution:

public static String concatenateBackwards(List<String> words)
{
   String str = "";
   ListIterator iter = words.listIterator(list.size());
   while (iter.hasPrevious())
  {
     str += iter.previous();
  }
  return str;  
}

Answer 2

You are declaring the String inside the loop

  while (iter.hasPrevious())
  {
     String str = iter.previous() + str; 
  }
  return str; 

Try

  String str ="";
  while (iter.hasPrevious())
  {
     str = iter.previous() + str; 
  }
  return str;