队列输出不正确？queue.offer()、queue.poll()和queue.peek()

Question

我应该为家庭作业做一个程序，它接受用户输入并显示特定的输出。我创建了一个数组队列，当我为它提供一个名称时，当我显示queue时，有时只会出现null。我不想要直接的答案，但我想了解数组队列是如何工作的，所以如果有人能给我指出正确的方向，我将不胜感激，谢谢。

public static MyQueue displayMenu(MyQueue queue) {
   // list of choices (array of Strings)
     String[] array = { "Offer Person", "Poll Person", "Peek Person", "Display Queue", "Exit Program"};
     int choice = 0;
  // display loop   
     while (choice != array.length-1) {
        choice = JOptionPane.showOptionDialog(null, // put in center of screen
           "Press a Button", // message to user
           "Queue (line) of People", // title of window
           JOptionPane.YES_NO_CANCEL_OPTION, // type of option
           JOptionPane.QUESTION_MESSAGE, // type of message
           null, // icon
           array, // array of strings
           array[array.length - 1]); // default choice (last one)

        if(choice == 0) {
           String name = JOptionPane.showInputDialog(null, "Enter person's name");  
           queue.offer(name); 
        }
        if(choice == 1) {

           JOptionPane.showMessageDialog(null, queue.poll() + " is next in line.");  

        }
        if(choice == 2) {

           JOptionPane.showMessageDialog(null, queue.peek() + " is in front of the line.");


        }
        if(choice == 3) {
           String output = queue.toString();
           JOptionPane.showMessageDialog(null, output);
        }

     }
     return queue;
   }//close displayMenu
  }

这段代码是我的class MyQueue<T> extends ArrayQueue<T> {的一部分

public String toString( ) {
  String s = "";
  for (int i = 0; i < currentSize; i++) {//loop through array and wrap around      
     endIndex = (endIndex + 1) % maxSize;
     s += "\n"+array[i];   
  } 
  return s; 
}

Answer 1

这个ArrayQueue类是你自己的实现吗？我怀疑可能有问题，否则您的displayMenu代码看起来是正确的。下面是一个可以测试的SSCCE类。我已经为队列使用了ArrayDeque。

import java.util.ArrayDeque;

import javax.swing.*;

public class QueueTest {

  public static MyQueue<String> displayMenu(MyQueue<String> queue) {
    // list of choices (array of Strings)
    String[] array = {"Offer Person", "Poll Person", "Peek Person", "Display Queue", "Exit Program"};
    int choice = 0;
    // display loop
    while (choice != array.length - 1) {
      choice = JOptionPane.showOptionDialog(null, // put in center of screen
                                            "Press a Button", // message to user
                                            "Queue (line) of People", // title of window
                                            JOptionPane.YES_NO_CANCEL_OPTION, // type of option
                                            JOptionPane.QUESTION_MESSAGE, // type of message
                                            null, // icon
                                            array, // array of strings
                                            array[array.length - 1]); // default choice (last one)

      switch(choice) {
        case 0:
          String name = JOptionPane.showInputDialog(null, "Enter person's name");
          queue.offer(name);
          break;
        case 1:
          JOptionPane.showMessageDialog(null, queue.poll() + " is next in line.");
          break;
        case 2:
          JOptionPane.showMessageDialog(null, queue.peek() + " is in front of the line.");
          break;
        case 3:
          String output = queue.toString();
          JOptionPane.showMessageDialog(null, output);
          break;
        case 4:
          System.out.println("Exiting program");
          break;
        default:
          System.out.println("Choice not valid");
          break;
      }
    }
    return queue;
  }//close displayMenu

  static class MyQueue<T>
    extends ArrayDeque<T> {
    public MyQueue() {
    }
  }

  public static void main(String[] args) {
    MyQueue<String> myQueue = new MyQueue<String>();
    displayMenu(myQueue);
  }
}