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好的，所以我討厭在一個如此模糊的問題上尋求幫助，但是我現在正在開發一個項目，它似乎沒有得到任何編譯時錯誤，但不會做有什麼要求。簡而言之，這個項目是一個鏈接列表（無序列表，具體），作爲文本編輯器。它將一個文件作爲命令行參數，然後將每個單獨的文檔行作爲節點存儲在列表中。無論是否確實這樣做，我都不知道，但是之後程序會根據請求接收特定的命令（鍵盤輸入）並編輯或列出文件的文本。LinkedList程序無響應;可能的空指針錯誤
問題是，我甚至無法分辨文件是否存儲在列表中，因爲每次我給列表中的命令L時，程序只是「跳過」它並繼續，就好像沒有任何東西問它。可能是因爲任何原因沒有存儲該文件，或者unorderedList類的toString方法可能存在問題。
我所有的類的代碼如下：
public class LinearNode<T> {
//Begin by declaring the basic node and its data
private LinearNode<T> next;
private T element;
public LinearNode() {
//The basic null constructor
next = null;
element = null;
}
public LinearNode(T elem) {
//The overloaded constructor to create a node
next = null;
element = elem;
}
public LinearNode<T> getNext() {
//Get the node reference
return next;
}
public void setNext(LinearNode<T> node) {
//Create or redirect a node reference
next = node;
}
public T getElement() {
//Get the actual data stored in the node
return element;
}
public void setElement(T elem) {
//Create or redirect the node's data
element = elem;
}
}
而對於名單
public abstract class LinkedList<T> implements ListADT<T>, UnorderedListADT<T> {
protected int count;
protected LinearNode<T> head, tail;
protected int modCount;
public LinkedList() {
count = 0;
head = null;
tail = null;
head = tail;
head.setNext(tail);
modCount = 0;
}
public T remove(T targetElement) throws EmptyCollectionException, ElementNotFoundException {
if(isEmpty())
throw new EmptyCollectionException("LinkedList");
boolean found = false;
LinearNode<T> previous = null;
LinearNode<T> current = head;
while(current!=null&&!found) {
if(targetElement.equals(current.getElement())) {
found = true;
}
else {
previous = current;
current = current.getNext();
}
}
if(!found)
throw new ElementNotFoundException("Linked List");
if(size()==1) {
head = tail = null;
}
else if(current.equals(head))
head = current.getNext();
else if(current.equals(tail)) {
tail = previous;
tail.setNext(null);
}
else {
previous.setNext(current.getNext());
}
count--;
modCount++;
return current.getElement();
}
}
import java.util.Iterator;
public class UnorderedList<T> extends LinkedList<T>{
public UnorderedList() {
super();
}
public void addToFront(T element) {
if(head==null) {
head = new LinearNode<T>(element);
if(tail==null) {
tail = head;
}
count++;
modCount++;
}
else {
LinearNode<T> current = head;
head.setElement(element);
head.setNext(current);
count++;
modCount++;
}
}
public void addToRear(T element) {
if(tail.getElement()==null) {
tail.setElement(element);
count++;
modCount++;
}
else {
LinearNode<T> current = tail;
tail = new LinearNode<T>(element);
current.setNext(tail);
count++;
modCount++;
}
}
public void addAfter(T element, T target) {
LinearNode<T> current = head;
LinearNode<T> node = new LinearNode<T>(element);
LinearNode<T> temp = null;
while(!(current.getElement()==target)) {
current = current.getNext();
}
if(!(current.getNext()==null)) {
temp = current.getNext();
//temp.setElement(current.getElement());
}
current.setNext(node);
node.setNext(temp);
count++;
modCount++;
}
public T removeLast() {
T last = tail.getElement();
tail = null;
LinearNode<T> current = head;
while(!(current.getNext()==null)) {
current = current.getNext();
}
current = tail;
count--;
modCount++;
return last;
}
public int size() {
return count;
}
public Iterator<T> iterator() {
Iterator<T> itr = this.iterator();
return itr;
}
public boolean isEmpty() {
boolean result = false;
if(head==null&&tail==null) {
result = true;
}
else
result = false;
return result;
}
public T first() {
return head.getElement();
}
public T last() {
return tail.getElement();
}
public boolean contains(T elem) {
boolean result = false;
for(T element : this) {
if(element==elem) {
result = true;
break;
}
}
return result;
}
public T removeFirst() {
LinearNode<T> current = head;
head = current.getNext();
count--;
modCount++;
return current.getElement();
}
public String toString() {
LinearNode<T> current = head;
String s = "";
for(int countA=0;countA<count;count++) {
s += (countA+1)+"> "+current.getElement()+"\n";
current = current.getNext();
}
return s;
}
}
和主編輯器
import java.util.Scanner;
import java.util.Iterator;
import java.io.*;
public class myEditor {
public static void saveToFile(String text, String filename) throws IOException{
PrintWriter out = new PrintWriter(new File(filename));
out.println(text);
out.close();
}
public static void main(String args[]) {
boolean quit = false;
try {
if(args.length!=1) {
throw new IllegalArgumentException();
}
String filename = args[0];
Scanner input = new Scanner(new File(filename));
//Add exception
UnorderedList<String> list = new UnorderedList<String>();
while(input.hasNextLine()) {
if(list.head==null) {
list.addToFront(input.nextLine());
}
list.addToRear(input.nextLine());
}
System.out.println(">");
do {
Scanner command = new Scanner(System.in);
String comm = command.next();
String[] comm1 = comm.split(" ");
if(comm1.length==1) {
if(comm1[0].equalsIgnoreCase("I")) {
System.out.println("Type a line of text >");
comm = command.next();
list.addToRear(comm);
}
else if(comm1[0].equalsIgnoreCase("L")) {
System.out.print(list.toString());
}
else if(comm1[0].equalsIgnoreCase("E")) {
saveToFile(list.toString(), filename);
quit = true;
break;
}
}
else {
if(comm1[0].equalsIgnoreCase("I")) {
int linNum = Integer.parseInt(comm1[1]);
Iterator<String> itr = list.iterator();
String current = "";
for(int count=0;count<linNum;count++) {
current = itr.next();
}
list.addAfter(comm, current);
}
else if(comm1[0].equalsIgnoreCase("D")) {
int linNum = Integer.parseInt(comm1[1]);
if(linNum<=list.count&&linNum>0) {
Iterator<String> itr = list.iterator();
String current = "";
for(int count=0;count<linNum;count++) {
current = itr.next();
}
list.remove(current);
}
}
}
}
while(!quit);
}
catch(IllegalArgumentException e) {
System.err.print(e.getMessage());
}
catch(FileNotFoundException e) {
System.err.print(e.getMessage());
}
catch(IOException e) {
System.err.print(e.getMessage());
}
}
}
還有一些其他類和一些接口，但對於我遇到的問題，我不認爲它們是相關的。
有沒有人看到這裏可能發生了什麼，或者我可能寫錯了什麼導致我的程序忽略命令？
不應該將您創建的類定義爲通用類（即'LinearNode'）？ –
Paolo
您是否嘗試過使用調試器？如果這不是一個選項：在讀取列表之後但在獲取命令之前顯示System.out.println（list.size（））是什麼？ –
@Paolo：他們是;但由於格式不正確而不可見。 – Holger