我的Iterator和Deque方法有问题，而且这是我的代码：
import java.util.*;
import java.util.Iterator;
class Customer {
public String lastName;
public String firstName;
public Customer() {
}
public Customer(String last, String first) {
this.lastName = last;
this.firstName = first;
}
public String toString() {
return firstName + " " + lastName;
}
}
class HourlyCustomer extends Customer {
public double hourlyRate;
public HourlyCustomer(String last, String first) {
super(last, first);
}
}
class GenQueue<E> {
private LinkedList<E> list = new LinkedList<E>();
public ListIterator<E> iterator = list.listIterator();
public void enqueue(E item) {
list.addLast(item);
}
public E dequeue() {
return list.poll();
}
public E show(){
return list.peek();
}
public void printQueueElements(){
}
public E isNotEnd(){
return list.getLast();
}
public boolean hasItems() {
return !list.isEmpty();
}
public boolean isEmpty()
{
return list.isEmpty();
}
public Iterator<E> iterator()
{
return iterator;
}
public E removeFirst(){
return list.removeFirst();
}
public E getFirst(){
return list.getFirst();
}
public int size() {
return list.size();
}
public boolean hasNext()
{
return false;
}
public void addItems(GenQueue<? extends E> q) {
while (q.hasNext()) list.addLast(q.dequeue());
}
}
public class Jerald {
public static void main(String[] args){
Scanner sc = new Scanner(System.in);
String input1;
String input2;
int choice = 1000;
GenQueue<Customer> empList;
empList = new GenQueue<Customer>();
GenQueue<HourlyCustomer> hList;
hList = new GenQueue<HourlyCustomer>();
while(true){
do{
System.out.println("================");
System.out.println("Queue Operations Menu");
System.out.println("================");
System.out.println("1,Enquene");
System.out.println("2,Dequeue");
System.out.println("0, Quit\n");
System.out.println("Enter Choice:");
try{
choice = sc.nextInt();
switch(choice){
case 1:
do{
System.out.println("\nPlease enter last name: ");
input1 = sc.next();
System.out.println("\nPlease enter first name: ");
input2 = sc.next();
hList.enqueue(new HourlyCustomer(input1, input2));
empList.addItems(hList);
System.out.println("\n"+(input2 + " " + input1) + " is successful queued");
System.out.println("\nDo you still want to enqueue?<1> or do you want to view all in queue?<0> or \nBack to main menu for dequeueing?<menu>: ");
choice = sc.nextInt();
}while (choice != 0);
System.out.println("\nThe customers' names are: \n");
int numberOfElements = empList.size();
for (int i = 0; i < numberOfElements; i++) {
Customer emp = empList.dequeue();
System.out.println(emp.firstName + " " + emp.lastName + "\n");
empList.enqueue(emp);
}
break;
case 2:
if (empList.isEmpty()) {
System.out.println("The queue is empty!");
}
else
{
System.out.println("\nDequeued customer: " +empList.getFirst());
empList.removeFirst();
}
if (empList.isEmpty()) {
System.out.println("The queue is empty!");
}
else
{
System.out.println("\nNext customer in queue: " +empList.getFirst()+"\n");
}
break;
case 0:
System.exit(0);
default:
System.out.println("Invalid choice");
}
}
catch(InputMismatchException e){
System.out.println("Please enter 1-5, 0 to quit");
sc.nextLine();
}
}while(choice != 0);
}
}
}
在第一种情况下，我试图让它检索队列中的所有元素并将其打印出来。没有从那里删除它们。所以基本上，不是使用我完成的while(hasItems)和poll()，而是显示了我想要的输出，但它删除了列表中的所有内容，所以我提出了另一种方法并使用了hasNext方法，所以我将while(empLst.hasNext())与element()方法一起使用，该方法仅检索但不删除。不幸的是，我在这方面失败了并且在许多输入之后得到了一个空结果，或者在给出一个输入之后得到了一个无限循环。我该如何解决？需要帮忙。我认为这是我的实施，但我想我已经检查过了。无论如何，我需要你的意见。
答案 0 :(得分：0)
在案例1中，在do-while循环之后，您想要打印队列中的所有元素并保留所有元素。
我看到了两种可能性：
1）在GenQueue中实现一种迭代内部列表并打印每个元素而不改变任何内容的方法：public void printQueueElements（）。 这是推荐的解决方案。
2）而不是：
while (empList.hasNext()) {
Customer emp = empList.dequeue();
System.out.println(emp.firstName + " " + emp.lastName + "\n" );
}
使用：
int numberOfElements = empList.size();
for (int i = 0; i < numberOfElements; i++) {
Customer emp = empList.dequeue();
System.out.println(emp.firstName + " " + emp.lastName + "\n");
empList.enqueue(emp);
}
这样队列重新获得了它的元素。
案例3的代码应为：
case 3:
System.out.println("\nThe customers' names are: \n");
Iterator<Customer> it = empList.iterator();
注意变量的类型＆＃34;它＆＃34;。此外，惯例是调用迭代器变量＆＃34; itr＆＃34;或＆＃34;迭代器＆＃34;。
答案 1 :(得分：0)
要摆脱无限循环问题，请删除外部while（true）循环。导致无限循环正是这些循环的作用，你不需要它来获得你想要的那种流。
我还在你的菜单中引入了第三种选择，它可以清除一些东西，但我想这取决于你。
就你的列表问题而言，修复GenQueue中的“dequeue”方法，使它实际出一个dequeue（删除列表中的第一个元素），然后你的案例2变得容易了。
要打印列表而不删除其元素，请使用迭代器。我删除了队列类中的ListIterator字段，因为您不需要它。实际上，无论如何，您已经为该类实现了大多数方法。看看吧 List API
class GenQueue<E> {
private LinkedList<E> list = new LinkedList<E>();
public void enqueue(E item) {
list.addLast(item);
}
public E dequeue() {
// return a customer with null values if empty? (up to you)
if (list.isEmpty())
return new Customer("","");
else
return list.remove(0);
}
public E isNotEnd(){
return list.getLast();
}
public boolean hasItems() {
return !list.isEmpty();
}
public boolean isEmpty() {
return list.isEmpty();
}
public Iterator<E> iterator() {
return list.iterator();
}
public E removeFirst() {
return list.removeFirst();
}
public E getFirst() {
return list.getFirst();
}
public int size() {
return list.size();
}
public boolean hasNext() {
return false;
}
public void addItems(GenQueue<? extends E> q) {
while (q.hasNext()) list.addLast(q.dequeue());
}
}
public class something {
public static void main(String[] args) {
Scanner sc = new Scanner(System.in);
String input1;
String input2;
int choice = 1000;
GenQueue<Customer> empList;
empList = new GenQueue<Customer>();
GenQueue<HourlyCustomer> hList;
hList = new GenQueue<HourlyCustomer>();
do {
System.out.println("================");
System.out.println("Queue Operations Menu");
System.out.println("================");
System.out.println("1,Enquene");
System.out.println("2,Dequeue");
System.out.println("3,View queue");
System.out.println("0, Quit\n");
System.out.println("Enter Choice:");
try {
choice = sc.nextInt();
switch(choice) {
case 1:
System.out.println("\nPlease enter last name: ");
input1 = sc.next();
System.out.println("\nPlease enter first name: ");
input2 = sc.next();
hList.enqueue(new HourlyCustomer(input1, input2));
empList.addItems(hList);
System.out.println("\n"+(input2 + " " + input1) + " is successful queued");
break;
case 2:
System.out.println("Dequeued customer: " + empList.dequeue().toString());
break;
case 3:
System.out.println("\nThe customers' names are: \n");
Iterator<Genqueue<Customer>> it = empList.iterator();
while (it.hasNext()) {
Customer emp = it.next();
System.out.println(emp.firstName + " " + emp.lastName + "\n" );
}
break;
case 0:
System.exit(0);
default:
System.out.println("Invalid choice");
}
}
catch(InputMismatchException e) {
System.out.println("Please enter 1-5, 0 to quit");
sc.nextLine();
}
} while(choice != 0);
}
}