Remove element in linked list linked list

Question

here's my codes
public class Student
    private String name, matric;
    public Student(){}
    public Student( String name, String matric)
       this.name = name;
       this.matric = matric;
     public String getName()
     { return name;}
     public void setName(String name)
     { this.name = name;}
     public String getMatric()
     { return matric;}
     public void setMatric( String matric)
     { this.matric = matric;}
     public String toString()
        return "Name: " + name + ", Matric no: " + matric + "\n";   
    }// end student classthe link list class
public class LinkedList extends java.util.LinkedList
    // instance variables - replace the example below with your own
    private ListNode firstNode;
    private ListNode lastNode;
    private ListNode currNode;
    private String name;
     * Constructor for objects of class LinkedList
    public LinkedList(String s)
        name = s;
        firstNode = lastNode = currNode = null;
    public LinkedList() {this("list");}
    public synchronized void insertAtFront(Object insertItem) {
        if (isEmpty())
            firstNode = lastNode = new ListNode(insertItem);
        else
            firstNode = new ListNode(insertItem, firstNode);
    public synchronized void insertAtBack(Object insertItem) {
        if (isEmpty())
            firstNode = lastNode = new ListNode(insertItem);
        else
            lastNode = lastNode.next = new ListNode(insertItem);
    public synchronized Object removeFromFront() throws EmptyListException {
        Object removeItem = null;
        if (isEmpty())
            throw new EmptyListException(name);
            removeItem = firstNode.data;
            if (firstNode.equals(lastNode))
                firstNode = lastNode = null;
            else
                firstNode = firstNode.next;
            return removeItem;    
    public synchronized Object removeFromBack() throws EmptyListException {
        Object removeItem = null;
        if (isEmpty()) throw new EmptyListException(name);
        removeItem = lastNode.data;
        if (firstNode.equals(lastNode))
            firstNode = lastNode = null;
        else {
            ListNode current = firstNode;
            while (current.next != null)
                current = current.next;
            lastNode = current;
            current.next = null;
        return removeItem;
    public synchronized boolean isEmpty()
    { return firstNode == null;}
    public synchronized Object getFirst() {
        if (isEmpty())
            return null;
           else {
                currNode = firstNode;
                return currNode.data;
    public synchronized Object getNext() {
        if (currNode != lastNode) {
            currNode = currNode.next;
            return currNode.data;
        else
            return null;
    public synchronized String print() {
        String out = "";
        if (isEmpty()) {
            out = "Empty "+ name;
        out = "The "+ name+ " is:\n";
        ListNode current = firstNode;
        while (current != null) {
            out += ""+ current.data.toString();
            current = current.next;
        return out;
    public synchronized Object getLast() {
        if (isEmpty())
            return null;
        else {
            currNode = lastNode;
            return currNode.data;
}// end LinkedListand the application class
import java.io.*;
import java.util.*;
import javax.swing.*;
public class StudentAppLL
    public static void main(String[] args) throws IOException {
        LinkedList std = new LinkedList();
        BufferedReader br = new BufferedReader(new FileReader("studentIn.txt"));
        PrintWriter pw = new PrintWriter(new BufferedWriter(new FileWriter("studentOut.txt")));
        String line = br.readLine();
        while (line != null) {
            StringTokenizer tk = new StringTokenizer(line);
            while (tk.hasMoreTokens()) {
                String n = tk.nextToken();
                String m = tk.nextToken();
                Student a = new Student(n, m);
                std.insertAtFront(a);
                line = br.readLine();
        std.print();
        System.out.print(std.getFirst());
        Student data = (Student)std.getFirst();
        String matric;
        String nm = "Zaki";
        while (data != null) {
            if (data.getName().equalsIgnoreCase(nm)) {
                System.out.print(data.getName()+ " ada\n");
                //std.re
                data = (Student)std.getNext();  
        Student b = new Student("Umar","2004163943");
        std.insertAtBack(b);
        String name = "", matric = "", s = "";
        boolean stop = false;
        int size = std.size();
        JOptionPane.showMessageDialog(null, size);
        s = JOptionPane.showInputDialog("A: Add Student\nR: Remove Student" +
                                       "\nV: View Sorted Student List\nS: Stop ");
        while(!stop){
            if (s.equalsIgnoreCase("A")){
                name = JOptionPane.showInputDialog("Enter student name: ");
                matric = JOptionPane.showInputDialog("Matric number: ");
                Student student = new Student(name, matric);
                std.insertAtBack(student);
                s = JOptionPane.showInputDialog("A: Add Student\nR: Remove Student" +
                                       "\nV: View Sorted Student List\nS: Stop ");
            else if (s.equalsIgnoreCase("R")){
                Student data = (Student)std.getFirst();
                Student first = (Student)std.getFirst();
                Student last = (Student)std.getLast();
                JOptionPane.showMessageDialog(null, "First: "+ first+ "\nLast: "+ last);
                String ns = JOptionPane.showInputDialog("Enter the student's name");
                while (data != null) {
                    // buang kalau pd bhgn dpn
                    if (data.getName().equalsIgnoreCase(ns) && ns.equalsIgnoreCase(first.getName())) {
                        JOptionPane.showMessageDialog(null, first.getName());
                        JOptionPane.showMessageDialog(null, data.getName()+ " kena buang");
                        //std.removeFromFront();
                        std.remove(data);
                        s = JOptionPane.showInputDialog("A: Add Student\nR: Remove Student" +
                                       "\nV: View Sorted Student List\nS: Stop ");                                       
                     if (data.getName().equalsIgnoreCase(ns) && ns.equalsIgnoreCase(last.getName())) {
                        std.removeFromBack();
                        JOptionPane.showMessageDialog(null, data.getName()+ " kena buang");
                         s = JOptionPane.showInputDialog("A: Add Student\nR: Remove Student" +
                                       "\nV: View Sorted Student List\nS: Stop ");
                     data = (Student)std.getNext();  
                }// habis while loop
            // keluar jika pilih 's'
            else if (s.equalsIgnoreCase("S")){ stop = true;}
            else { JOptionPane.showMessageDialog(null, "Wrong input"); }                    
        JOptionPane.showMessageDialog(null, std.print());
        br.close();
        pw.close();
    }// end main class
}and here's the studentIn.txt data
Ahmad 2004199877
Hanif 2005378219
Zaki 2004456790
how can i do it? i mean to remove other than first element?
Message was edited by:
ikki_72

Answer 1

> public class LinkedList extends java.util.LinkedList
// instance variables - replace the example below with your own
private ListNode firstNode;
private ListNode lastNode;
private ListNode currNode;
private String name;
[ ... ]Eeeeeeeeeew! Don't do that ever again! A java.util.LinkedList is very
well capable of managing a linked list (it is a linked list after all).
Either build your own linked list mechanics or use a LinkedList as
one of the member variables of your class, but please don't do this.
kind regards,
Jos ( ... that was scary ... )