java - LinkedList 头尾问题

Question

我试图弄清楚为什么 InventoryList.java 中的某些循环不起作用，例如所有的删除方法。不工作，我的意思是我实现的循环不起作用，我正在寻找如何修复它的解决方案。另一个不太重要的问题是 InventoryList.java 中的 toString() 设置不正确，但我想知道为什么我的循环不起作用。有关更多信息，以下是我用来实现这些类的文档： http: //cs300-www.cs.wisc.edu/wp/wp-content/uploads/2020/12/p7/doc/package-summary .html

感谢您阅读

/**
 * This class models a Box used for inventory
 * 
 * @author mouna
 *
 */
public class Box {
  private static int nextInventoryNumber = 1; // generator of unique inventory numbers
  private Color color; // color of this box
  private final int INVENTORY_NUMBER; // unique inventory number of this box

  /**
   * Creates a new Box and initializes its instance fields color and unique inventory number
   * 
   * @param color color to be assigned of this box. It can be any of the constant color values
   *              defined in the enum Color: Color.BLUE, Color.BROWN, or Color.YELLOW
   */
  public Box(Color color) {
    this.color = color;
    this.INVENTORY_NUMBER = nextInventoryNumber++;
  }

  /**
   * Returns the color of this box
   * 
   * @return the color of this box
   */
  public Color getColor() {
    return color;
  }

  /**
   * returns the inventory number of this box
   * 
   * @return the unique inventory number of this box
   */
  public int getInventoryNumber() {
    return this.INVENTORY_NUMBER;
  }


  /**
   * Returns a String representation of this box in the format "color INVENTORY_NUMBER"
   *
   * @return a String representation of this box
   */
  @Override
  public String toString() {
    return this.color + " " + this.INVENTORY_NUMBER;
  }

  /**
   * This method sets the nextInventoryNumber to 1. This method must be used in your tester methods
   * only.
   */
  public static void restartNextInventoryNumber() {
    nextInventoryNumber = 1;
  }
}

/**
 * This Enumeration groups the name of constants representing the three colors BLUE, BROWN, and YELLOW
 *
 */
public enum Color{
  BLUE, BROWN, YELLOW;
}

public class LinkedBox {
    private Box box;
    private LinkedBox next;
    
  //constructors
    public LinkedBox(Box box) {
    this.box = box;
    }
    
    public LinkedBox(Box box, LinkedBox next) {
    this.box = box;
    this.next = next;
    }
    
    //getters
    public Box getBox() {
        return box;
    }
    
    public LinkedBox getNext() {
        return next;
    }
    
    //setters
    public void setNext(LinkedBox next) {
        this.next = next;
    }
    
    public String toString() {
        if (next == null) return box.toString() + " -> END"; //one arg
        return box.toString() + " -> " + this.next; //two+ args
    }
}

public class InventoryList {
  private LinkedBox head;
  private LinkedBox tail;
  private int size;
  private int yellowCount;
  private int blueCount;
  private int brownCount;

  //TODO remove these 2 methods later
  public LinkedBox getHead() {
    return this.head;
  }
  
  public LinkedBox getTail() {
    return this.tail;
  }

  //getters
  public int getBlueCount() {
    return this.blueCount;
  }

  public int getBrownCount() {
    return this.brownCount;
  }

  public int getYellowCount() {
    return this.yellowCount;
  }

  public Box get(int index) {
    int count = 0;
    Box box = new Box(Color.BLUE);
    while (head != null) {
      if (count == index) box = this.head.getBox();
      head = head.getNext();
      count++;
    }
    return box;
  }

  public int size() {
    return this.size;
  }

  //setters
  public void addBlue(Box blueBox) {
    if (head.getBox().getColor() != Color.YELLOW || tail.getBox().getColor() == Color.BROWN) head = new LinkedBox(blueBox, head); this.blueCount++; this.size++;
  }

  public void addBrown(Box brownBox) {
    tail = new LinkedBox(brownBox, tail);
    this.brownCount++; this.size++;
  }

  public void addYellow(Box yellowBox) {
    head = new LinkedBox(yellowBox, head);
    this.yellowCount++; this.size++;
  }

  //removers
  public Box removeBox(int inventoryNumber) {
    Box box = new Box(Color.BLUE);
    int index = 0;
    while (head != null) {
      if (inventoryNumber == index) {
        box = head.getBox();
        head = null;
      }
      index++;
      head = head.getNext();
    }
    return box;
  }

  public Box removeBrown() {
    Box box;
    if (tail.getBox().getColor() == Color.BROWN) {
      box = tail.getBox();
      tail = null;
      return box;
    }
    return new Box(Color.BROWN);
  }

  public Box removeYellow() {
    Box box;
    if (head.getBox().getColor() == Color.YELLOW) {
      box = head.getBox();
      head = null;
      return box;
    }
    return new Box(Color.YELLOW);
  }

  public void clear() {
    while (head != null) {
      head = null;
      head = head.getNext();
    }
  }

  //miscellaneous
  public boolean isEmpty() {
    if (head == null && tail == null) return true;
    return false;
  }

  public String toString() {
    if (head == null || tail == null) return "";
    return head+" "+tail+" <-TO STRING";
  }
}

标签： javaoop

Answer 1

如果您没有使用任何集成开发环境 (IDE)，请使用一个，例如Eclipse。要了解代码是如何工作的，最好学习如何调试。

您的代码有多个问题。我会给你一些提示，剩下的就交给你了。首先修复toString()方法，以便您知道发生了什么。
在LinkedBox#toString()方法中，代码进行递归并打印整个链表。因为this.next.toString()被递归调用。将最后一行更改为：

return box.toString() + " -> " + this.next.getBox(); //

然后InventoryList#toString()像这样实现：

public String toString() {
    if (head == null || tail == null) return "";
        
    LinkedBox temporaryLinkedBox = head; //<-- use temporary variable
    StringBuilder result = new StringBuilder();
    while(temporaryLinkedBox!=null) {
        result.append(temporaryLinkedBox.toString()).append(" | ");
        temporaryLinkedBox = temporaryLinkedBox.getNext();
   }
   result.append(" <-TO STRING");
   return result.toString();
}

请注意我们如何不使用head迭代列表。我们正在使用临时变量temporaryLinedBox进行迭代。

同样的情况，InventoryList#getandInventoryList#removeBox和 get 方法不使用 head 来迭代列表。使用临时变量：

  public Box removeBox(int inventoryNumber) {
    Box box = null;
    int index = 0;
    LinkedBox temporaryLinkedBox = head;
    while (temporaryLinkedBox != null) {
      if (inventoryNumber == index) {
        box = temporaryLinkedBox.getBox();
        break;     //<-- use 'break' to exit loop
      }
      index++;
      temporaryLinkedBox = temporaryLinkedBox.getNext();
    }
    return box;
  }

注意：这只是一个示例代码，如果有任何错误，您必须调试和修复错误。