Question

I created a Linked List, with insert, search and remove functions. I also created a iterator for it. Now, suppose I do this:

myList<Integer> test = new myList(); test.insert(30); test.insert(20); test.insert(10); myList.iterator it = test.search(20); if(it.hasNext())     System.out.println(it.next()); 

And voila, it works (it prints the value of the element at the node, in this case 20). Now, if I do this:

myList<Double> test = new myList(); test.insert(30.1); test.insert(20.1); test.insert(10.1); myList.iterator it = test.search(20.1); if(it.hasNext())     System.out.println(it.next()); 

It doesn’t, because the iterator is pointing to null. Here is the implementation of the search function:

public iterator search(T data) {     no<T> temp = first;     while( (temp != null) && (temp.data != data) )         temp = temp.next;     return (new iterator(temp)); } 

Here’s how I know there’s something fishy with the comparisons: If I change part of the above code like this:

while( (temp != null) && (temp.data != data) )      System.out.println(temp.data + ' ' + data);      temp = temp.next; 

I can see it printing the numbers in the list. It prints, at one point, ‘20.1 20.1’ (for example). So how can I fix this? The function appears to be right, but it just seems as if Java isn’t comparing the numbers correctly.

EDIT: wth, BigDecimal gave me the same kind of problem too.

EDIT 2: equals() worked, didn’t realize something else was amiss. Sorry.

Answer 1

You don’t want the != operator for this. It comapres references. You want the .equals() method:

public iterator search(T data) {     no<T> temp = first;     while (!data.equals(temp.data)) {         temp = temp.next;     }     return (new iterator(temp)); } 

Also, watch out for auto-boxing. You may find that test.search(20.1) boxes 20.1 to a Float not a Double, which will probably break your comparison. Compare the results with test.search(20.1d). If I recall correctly, the expression:

new Float(20.1).equals(new Double(20.1)) 

is false.