Question

我正在处理的项目现在涉及我从文本文件中读取单词并将它们加载到数组中（最终是二叉树，但稍后将完成）。我必须将单词和单词的频率（最初为1）加载到数组中，因此我将两个变量都打包到对象WordNode中。我能够将单词加载到数组中，但是当我尝试检查单词是否已经存在于数组中时，事情就会崩溃。如果是，我必须将频率增加1.然而，我的代码甚至不检查单词并且无论如何只是添加它（我假设它正在检查对变量的引用而不是单词本身）。以下是我的main方法和WordNode类。

主要方法：

public class Driver {
/////////////// fields ///////////////
public static ArrayUnorderedList<WordNode> wordArray = new ArrayUnorderedList<WordNode>();
public static LinkedBinarySearchTree<WordNode> wordTree = new LinkedBinarySearchTree<WordNode>();   //tree to hold words

/////////////// methods ///////////////
public static void main(String[] args) throws Exception {
    //ask for filename       
    BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
    System.out.println("Enter the name of the file to read from: ");
    Reader file = new FileReader(reader.readLine());

    //read file
    Scanner input = new Scanner(file);

    while(input.hasNext()) {
        //get words from file
        String word = input.next();

        //remove non-word characters and convert to lowercase
        word = word.replaceAll("\\W", "");
        word = word.toLowerCase();

        //create node
        WordNode newWord = new WordNode(word);

        //if word is already in array
        if(wordArray.contains(newWord)) {
            System.out.println("Word is already in array");

            //increment frequency by 1
            int index = wordArray.find(newWord);
            wordArray.list[index].setFrequency(wordArray.list[index].getFrequency() + 1);
            System.out.println(newWord.getWord() + newWord.getFrequency());
        } else {
            System.out.println("Word is not yet in array");

            //add word to tree
            System.out.println(newWord.getWord());
            wordArray.addToRear(newWord);
        }
    }

    //insert into tree

    //perform traversals on tree
}

WordNode类：

public class WordNode {
   protected String word;
   protected WordNode left, right;
   protected int frequency;

   /**
    * Creates a new node with the specified data.
    * @param obj the element that will become a part of the new node
    */
   WordNode(String obj) {
      word = obj;
      left = null;
      right = null;
      frequency = 1;
   }

   /**
    * Gets the word.
    * @return the word
    */
   public String getWord() {
      return word;
   }

   /**
    * Sets the word.
    * @param word the word to set
    */
   public void setWord(String word) {
      this.word = word;
   }

   /**
    * Gets the left.
    * @return the left
    */
   public WordNode getLeft() {
      return left;
   }

   /**
    * Sets the left.
    * @param left the left to set
    */
   public void setLeft(WordNode left) {
      this.left = left;
   }

   /**
    * Gets the right.
    * @return the right
    */
   public WordNode getRight() {
      return right;
   }

   /**
    * Sets the right.
    * @param right the right to set
    */
   public void setRight(WordNode right) {
      this.right = right;
   }

   /**
    * Gets the frequency.
    * @return the frequency
    */
   public int getFrequency() {
      return frequency;
   }

   /**
    * Sets the frequency.
    * @param frequency the frequency to set
    */
   public void setFrequency(int frequency) {
      this.frequency = frequency;
   }
}

ArrayList类中的一些方法：

/**
* Returns true if this list contains the specified element.
* @param target the element that the list is searched for
* @return true if the target is in the list, false if otherwise 
*/
public boolean contains(T target) {
    return (find(target) != NOT_FOUND);
}

/**
* Returns the array index of the specified element, or the
* constant NOT_FOUND if it is not found.
* @param target the element that the list will be searched for
* @return the integer index into the array containing the target element, or the NOT_FOUND constant
*/
public int find(T target) {
    int scan = 0, result = NOT_FOUND;
    boolean found = false;

    if (!isEmpty()) {
       while (!found && scan < rear) {
          if (target.equals(list[scan])) {
              found = true;
          } else {
             scan++;
          }
       }
    }

    if (found) {
       result = scan;
    }

    return result;
}

Answer 1

您的代码不起作用的直接原因是ArrayUnorderedList#contains()可能依赖于equals()方法来确定条目是否在列表中。没有看到班级的定义，就不可能知道。

由于您没有提供equals()的覆盖，因此它使用了对象标识（默认来自Object），因此每个WordNode都与其他WordNode不同。

如果您想使用ArrayUnorderedList，则必须以正确的行为实施WordNode#equals()。

但是，您应该考虑使用Map<String,Integer>（或Map<String,WordNode>）来存储频率。这会快得多。

Answer 2

您需要在WordNode中覆盖eqauls：

public boolean equals(Object o) {
     if(o instanceof WordNode) {
        WordNode temp = (WordNode) o;
        return(temp.getWord().equals(this.word));
     }
     else
         System.out.println("Object o you passed is not a WordNode");
}

这样，如果两个不同的WordNode对象与word字段具有相同的String，则认为它们等于

如何调用等于：

WordNode n1 = new WordNode();
n1.setWord("test");

WordNode n2 = new WordNode();
n2.setWord("test");

System.out.println(n1.equals(n2));

所以equals接收一个Object类型的对象，但是当你在WordNode上调用equals时，你需要提供一个WordNode实例的对象，否则我所做的转换失败（你的例外）当然没有意义验证Object是否等于WordNode

检查元素是否已存在于Java数组中

2 个答案: