I'm searching for an exact value of a node in my Doubly LinkedList using the searchByName method. It doesn't show the data that I want even If I pass a value that is present in the LinkedList.

public void searchByName(String param) throws Exception{
    Node currentNode = start;
    String theFirstName = currentNode.firstName.toLowerCase();
    String theLastName = currentNode.lastName.toLowerCase();
    param = param.toLowerCase();
    if (start == null) {
        throw new Exception("List Underflow");
    }else{
        String id= "Student ID", ln="Last Name", fn="First Name", course="Course", section="Section", yl="Year Level";
        System.out.format("%-10s\t%-10s\t%-10s\t%-5s\t%-10s\t%s", id, ln, fn, course, section, yl);
        System.out.println();
        while(currentNode.next != null){
            if (param == theFirstName || param == theLastName) {
                System.out.format("%-10s\t%-10s\t%-10s\t%-5s\t%-15s\t%d", currentNode.studentID, currentNode.lastName, currentNode.firstName, currentNode.course, currentNode.section, currentNode.yearLevel);
                System.out.println();
            }else{
                System.out.println("Not found");
                break;

            }
            currentNode = currentNode.next;
        }
        if (currentNode.next == null){
            System.out.format("%-10s\t%-10s\t%-10s\t%-5s\t%-15s\t%d", currentNode.studentID, currentNode.lastName, currentNode.firstName, currentNode.course, currentNode.section, currentNode.yearLevel);
            System.out.println();
        }

    }

My main function:

public static void main(String[] args)  throws Exception {
 StudentRecord senators = new StudentRecord();
 senators.insertEnd("110007", "Lacson", "Ping", "BSCS", "BSCS-III-A", "Active",  3);
    senators.insertEnd("110008", "Angara", "Sonny", "BSCS", "BSCS-III-B", "InActive",  3);
  senators.searchByName("Lacson");
}

Link to gist: https://gist.github.com/30b27d3612f95fc2ced99f50c4f23c14

CodePudding user response：

You are not updating theFirstName and theLastName when changing nodes.

Also, compare strings with equals, not ==.

CodePudding user response：

You have many bugs in your method 2 major ones:

1. Strings should be compared with equals method not ==
2. Your algorithm to traverse the list is wrong
3. Always use your own exception (LinkedListOutOfBoundsException)
4. Do not modify input parameters inside the function
5. Unnecessary else statement since it throws.
6. The last if is absolutely useless.
7. Try to use a logger

    public void searchByName(String param) throws LinkedListOutOfBoundsException {
        if (null == start) {
            throw new LinkedListOutOfBoundsException("List Underflow");
        }
        if (null == param) {
            throw new IllegalArgumentException("param must not be null");
        }

        Node currentNode = start;    
        while (currentNode != null) {
            if (param.equalsIgnoreCase(currentNode.firstName) 
                    || param.equalsIgnoreCase(currentNode.lastName)) {
                break;
            }
            currentNode = currentNode.next;
        }
        if (null == currentNode) {
            LOGGER.info("Not found");
        } else {
            LOGGER.info("Found {}", param);
        }
    }