How to do this question?Need help~

[Belisarius]

I missed that, but the problem still remains. What happens the first time you attempt to add a node? "startingnode" is initialized as null when you instantiate the class. "curr" is set to "startingnode". "prev" is set to "curr". Hence, "prev" is null.

[Valmont]

Originally posted by Belisarius

Any guesses as to what will go wrong here? You'll get a NullPointerException (wish I had the spoiler tags from SomethingAwful right now).

You're funny.

[Sunshine]

(Very confusing)

public class StudentList{

private Student startingnode;

public studentList(){
startingnode=null; //startingnode is initialized as null
}

public void add(Student newNode){

Student curr;
Student prev;

curr=startingnode; //curr is set to startingnode
prev=null; //prev is set to null or curr?

while(curr!=null){
prev=curr; //prev is set to curr?or delete this code.
curr=curr.getNext();
}

prev.setNext(newNode);
newNode.setNext(curr);

}

[Belisarius]

Here is the sequence of events.

1: startingnode = null;
3: curr = startingnode; // startingnode is still null, and therefore so is curr
3: curr = curr.next(); // NullPointerException is thrown here

Now, there is code inbetween these points, but nothing that impacts on this set of events. You cannot call a method on a null object (with exceptions that are too advanced for this topic and don't apply in any case).