Unable to insert into LinkedList

[huiling25]

I don't know why the customer records cannot be inserted into the linked list and the head of the linked list keep pointing to null...

//ListNode.java
public class ListNode{
    private Object item;
    private ListNode next,head;
    public ListNode(Object newItem)
    {    item = newItem;    next = null;     }
    public ListNode(Object newItem, ListNode newNext)
    {    item = newItem;    next = newNext;    }
    public void setItem(Object newItem)
    {    item = newItem;    }
    public void setNext(ListNode newNext)
    {    next = newNext;    }
    public Object getItem()
    {     return item;    }
    public ListNode getNext()
    {    return next;    }}
 
//LinkedList.java
public class LinkedList{
    protected ListNode head; //pointer to the first object
    protected int numOfItems; //total number of objects
    public LinkedList()
    {    head = null;     numOfItems = 0; }
    public boolean isEmptyList(){
        if(numOfItems==0)  return true;
        else    return false;    }
    protected ListNode find(int index) {   
         ListNode   cur = head;
         if (index > numOfItems) return null;
         for (int count=1; count<index; count++)     cur = cur.getNext();
         return cur;}
    public boolean insert(int at, Object newItem)
    {    ListNode   pre, cur;
         if (at < 1 || at > numOfItems+1) return false;
            numOfItems++;
         if (at == 1){
            if (isEmptyList()) head = new ListNode(newItem);
            else head = new ListNode(newItem, head);
            return true;}
        pre = find(at-1);
    cur = pre.getNext();
    pre.setNext(new ListNode(newItem, cur));
    return true;}
    public int size()
    {    return numOfItems;    }
 
//Customer.java
public class Customer{
    protected int acc_id;
    protected String name,address,birthdate,phone_no;
    protected double balance, interest;
    protected String type;
    public Customer(){....} //default constructor
    public Customer(int id,int name....){....}
    //all the set and get methods 
 
//Main Program
Customer[] records = new Customer[30];
LinkedList custRecords = new LinkedList();
for(int i=0;i<records.length;i++){ records[i] = new Customer(); }
//ask user for filename
//call readfile(filename,records,custRecords)
public static void readfile(String filename,Customer[] record,LinkedList cust_list){
int i=0;
try{
         File file = new File(filename);
            Scanner readfile = new Scanner(file);
            while(readfile.hasNext()){
                  //read all inputs from file
                  //e,g, record[i].setID(readfile.nextInt());
                    cust_list.insert(i+1,record[i]); //Something wrong here?
                  i++;
             }
}catch(FileNotFoundException){
    System.out.println("File not found");
}}

[JosAH]

I don't know why the customer records cannot be inserted into the linked list and the head of the linked list keep pointing to null...

System.out.println() is a very good debugging tool. Sprinkle them all over your
code where you expect something fishy's going on and run your program again.

kind regards,

Jos

[huiling25]

Thanx for ur help~ I solved the problem already~

[JosAH]

Thanx for ur help~ I solved the problem already~

Great; care to elaborate on what the mistake was? (just for the posterity).

kind regards,

Jos