需要帮助在已排序的LinkedList中添加节点

Question

I'm trying to add a new Customer object (which should be node.data, not node) in sorted order by the customer object's name alphabetically. But it's not working. It's printing out the list in unsorted order (unchanged from original order).

public void  add(Customer newNode, int dummy){
   if (head == null){ // The first node
      head = tail = this;
      head.setData(newNode);
      size=1;
      return;

   }else{
       CustomerList last = null;
       for(CustomerList node = head; 
               node != null && node.getData().toString().compareTo(newNode.name) < 0; 
                    node = node.next){
          last = node; 

       }
       CustomerList newList = new CustomerList(newNode);
       newList.setNext(last.next);
       last.next = newList;
   }

} // add

Input of Customer objects from txt file. Should print out again but in alphabetical order (customer name).

10121,Airgo Fresh ods,OH,870023
10125,Bird Out fittered ,MI,870023
10134,Kit river ,IL,870023
10167,Mouin Gontaods,OR,870021
10178,Theiasu El senter,CA,870022

Code which reads data from txt file and creates objects and adds to list:

public void byCustomerName()
 {
 records = null;
 System.gc();
 CustomerList.setHead(null);
 records = new CustomerList();
 try
  {
  String line;
  StringTokenizer st;
  String id, name, state, salesrep;
  BufferedReader infile = new BufferedReader(new FileReader("Customer.txt"));
  while ((line = infile.readLine()) != null)
      {
      st = new StringTokenizer(line, ",");
      id = st.nextToken(",");
      name = st.nextToken(",");
      state = st.nextToken(",");
      salesrep = st.nextToken(",");
      records.add(new Customer(id, name, state, salesrep), 99);
      }
  infile.close();
  } catch (IOException x) { System.err.println(x); } 
 } // byCustomerName

Answer 1

I think your code has all sorts of problems in it. For one, I don't ever see you updating head or tail if you replace the first or last element. Also, there is no check for last potentially being null . It'll be hard to say more without knowing how some of your underlying CustomerList items work.

Answer 2

I actually did this same exact assignment two semesters ago but decided to take the class again because I was unable to take the final. But since no programming for two semesters, I'm now extremely rusty. I'm just going to give up for now and use my old solution that I came up for the first time I took the class.

Solution:

public void add(Customer newNode, int dummy) {  
    CustomerList before = null;
    boolean inserted = false;
    if (head == null) {  //first node   
        head = tail = this;
        head.setData(newNode);
        return;
    } else {
        CustomerList curr = head;
        while(curr != null) {
            String currentName = curr.getData().getName();
            String newNodeName = newNode.name;
            if (currentName.compareToIgnoreCase(newNodeName) > 0) {

                CustomerList cList = new CustomerList(newNode);
                cList.setNext(curr);//curr is greater than clist, therefore cList's next element is curr
                if(before!=null)
                    before.setNext(cList);
                else {  //this tests the case when 
                    //the newNode goes at the BEGINNING of the list
                    head = cList;
                }
                curr = cList;
                inserted = true;
                return;
            }
            before = curr;
            curr = curr.next;               
        }
    }
    if(!inserted) {
        add(newNode);
    }

} // add

Answer 3

As Sudhanshu already told you can use Collections.sort(-) method on your List object or as an alternate just use TreeSet in case if you want unique objects. Its better to utilize inbuilt methods of java API as these are less error prone and more reliable, at the same time you can reduce your code and time to mug up in it.