verkettete Liste-Implementierung java

Ich habe implementiert eine verkettete Liste in Java. Ich habe alles erschaffen, aber ich habe Schwierigkeiten beim entfernen eines bestimmten Knotens mit spezifischen Daten. Es wirft ein NullPointerException. Ich glaube, ich bin immer ein NullPointerException weil der nächste Knoten ist null. Wenn jemand könnte, bitte zeigen mich in die richtige Richtung, das wäre toll.

Eingang

anything
one
two
three

Ausnahme:

Exception in thread "main" java.lang.NullPointerException
    at LinkedList.remove(LinkedList.java:28)
    at Main.main(Main.java:29)

Klassen:
LinkedList-Klasse

public class LinkedList {

    //fields
    private Node head;
    private Node last;
    private int size = 0;

    //constructor, used when the class is first called
    public LinkedList() {
        head = last = new Node(null);
    }

    //add method
    public void add(String s) {
        last.setNext(new Node(s));
        last = last.getNext();
        size++;
    }

    //remove method, if it returns false then the specified index element doens not exist
    //otherwise will return true
    public boolean remove(String data) {
        Node current = head;
        last = null;
        while(current != null) {
            if(current.getData().equals(data)) {
                current = current.getNext();
                if(last == null) {
                    last = current;
                }else {
                    last.getNext().setNext(current);
                    size--;
                    return true;
                }
            }else {
                last = current;
                current = current.getNext();
            }
        }
        return false;
    }
    //will return the size of the list - will return -1 if list is empty
    public int size() {
        return size;
    }

    //will check if the list is empty or not
    public boolean isEmpty() {
        return true;
    }

    //@param (index) will get the data at specified index
    public String getData(int index) {

        if(index <= 0) {
            return null;
        }

        Node current = head.getNext();
        for(int i = 1;i < index;i++) {
            if(current.getNext() == null) {
                return null;
            }
            current = current.getNext();
        }

        return current.getData();
    }

    //@param will check if the arguement passed is in the list
    //will return true if the list contains arg otherwise false
    public boolean contains(String s) {
        for(int i = 1;i<=size();i++) {
            if(getData(i).equals(s)) {
                return true;
            }
        }
        return false;
    }

    //@return contents of the list - recursively 
    public String toString() {
        Node current = head.getNext();
        String output = "[";
        while(current != null) {
            output += current.getData()+",";
            current = current.getNext();
        }
        return output+"]";
    }

    //@return first node
    public Node getHead() {
        return head;
    }

    //@return (recursively) list
    public void print(Node n) {
        if(n == null) {
            return;
        }else {
            System.out.println(n.getData());
            print(n.getNext());
        }
    }
}

Main

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Main {

    static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

    public static void main(String[] args) throws IOException{
        LinkedList list = new LinkedList(); //declaring main linked list
        LinkedList b_List = new LinkedList(); //declaring the backup list

        String input = null;
        //getting input from user, will stop when user has entered 'fin'
        while(!(input = br.readLine()).equals("fin")) {
            list.add(input); //adding to main list
            b_List.add(input);
        }

        list.print(list.getHead().getNext());

        System.out.println("Input Complete.");
        if(list.size() == 1) {
            System.out.println("You have entered only one name. He/She is the survior");
        }else {
            System.out.println("Enter the name(s) would like to remove: ");
            while(b_List.size() != 1) {
                String toRemove = br.readLine();
                b_List.remove(toRemove);
            }
        }
        System.out.println("The contestants were: ");
        list.print(list.getHead().getNext());
    }
}

Knoten

public class Node {

    //Fields
    private String data;
    private Node next;

    //constructor
    public Node(String data) {
        this(data,null);
    }

    //constructor two with Node parameter
    public Node(String data, Node node) {
        this.data = data;
        next = node;
    }

    /**
     * Methods below return information about fields within class
     * */

    //@return the data
    public String getData() {
        return data;
    }

    //@param String data to this.data
    public void setData(String data) {
        this.data = data;
    }

    //@return next
    public Node getNext() {
        return next;
    }
    //@param Node next set to this.next
    public void setNext(Node next) {
        this.next = next;
    }

}

InformationsquelleAutor Jeel Shah | 2011-12-19