代码是正确的，虽然它编译为“找不到符号＆＃39;

Question

我试图创建类isPalindrome并调用StackArrayBased和QueueArrayBased虽然编译错误表明我的逻辑错误？我似乎无法找到为什么它找不到这两个类的问题。首先我给了我的Palindrome代码，以下是我试图调用的两个类。

import java.util.Scanner;

public class isPalindrome {

public static void main(String[] args){
    Scanner scan  = new Scanner(System.in);
    System.out.println("Word to check: ");

    String userInput = scan.nextLine();
    userInput = userInput.toUpperCase();
    System.out.print(isPal(userInput)+" ");


}

public static boolean isPal(String str){
    QueueArrayBased aQueue = new QueueArrayBased();
    StackArrayBased aStack = new StackArrayBased();

    for (int i = 0; i < str.length(); i++){
        aQueue.enqueue(str.charAt(i));
        aStack.push(str.charAt(i));
    }

    //start to compare

    while(!aQueue.isEmpty()){
        if(aQueue.dequeue() != aStack.pop()){
            return false;
        }
    }

StackArrayBased

import ListReferenceBased.*;

public class StackArrayBased implements StackInterface
{
final int MAX_STACK = 50;  // maximum size of stack
private Object[] items;
private int top, count;

public StackArrayBased()
{
items = new Object[MAX_STACK];
top = -1;
count = 0;
}  // end default constructor

public boolean isEmpty()
{
return (top < 0);
}  // end isEmpty

public boolean isFull()
{
return (top == MAX_STACK-1);
}  // end isFull

public void push(Object newItem) throws StackException
{
if (!isFull()) {
  items[++top] = newItem;
  count++;
} else {
  throw new StackException("StackException on " + "push: stack full");
}  // end if
}  // end push

public void popAll()
{
items = new Object[MAX_STACK];
top = -1;
count = 0;
}  // end popAll

public Object pop() throws StackException
{
if (!isEmpty()) {
    count--;
  return items[top--];
} else {
  throw new StackException("StackException on " + "pop: stack empty");
}  // end if
}  // end pop

public Object peek() throws StackException
{
if (!isEmpty()) {
  return items[top];
} else {
  throw new StackException("Stack exception on " + "peek - stack empty");
}  // end if
}  // end peek

public String toString()
{
    StringBuilder st = new StringBuilder();
    for( int i=0; i < count; i++){
    st.append(items[top+i]+" ");
}
    return st.toString();
}
}  // end StackArrayBased

QueueArrayBased

public class QueueArrayBased implements QueueInterface
{
private final int MAX_QUEUE = 50; // maximum size of queue
private Object[] items;
private int front, back, count;

public QueueArrayBased()
{
items = new Object[MAX_QUEUE];
front = 0;
back = MAX_QUEUE-1;
count = 0;
}  // end default constructor

// queue operations:
public boolean isEmpty()
{
return count==0;
}  // end isEmpty

public boolean isFull()
{
return count==MAX_QUEUE;
}  // end isFull

public void enqueue(Object newItem) throws QueueException
{
if (!isFull()) {
  back = (back+1)%MAX_QUEUE;
  items[back] = newItem;
  ++count;
} else {
  throw new QueueException("QueueException on enqueue: Queue full");
}  // end if
}  // end enqueue

public Object dequeue() throws QueueException
{
if (!isEmpty()) {
  // queue is not empty; remove front
  Object queueFront = items[front];
  front = (front+1)%MAX_QUEUE;
  --count;
  return queueFront;
} else {
  throw new QueueException("QueueException on dequeue: Queue empty");
}   // end if
}  // end dequeue

public void dequeueAll()
{
items = new Object[MAX_QUEUE];
front = 0;
back = MAX_QUEUE-1;
count = 0;
}  // end dequeueAll

public Object peek() throws QueueException
{
if (!isEmpty()) {
  // queue is not empty; retrieve front
  return items[front];
} else {
  throw new QueueException("Queue exception on peek: Queue empty");
}  // end if
}  // end peek


public String toString()
{
 StringBuilder st = new StringBuilder();
     for(int i = 0; i < count; i++){
         st.append(items[front+i]+" ");
     }
 return st.toString();
} // end of toString

``} //结束QueueArrayBased