从文件中读取一个单词

Question

如果有人可以帮我弄清楚如何搜索文件中是否存在某个单词，我将非常感激。我知道如何阅读整个文本文件。

这就是我到目前为止所拥有的：

public static void main(String[] args) throws IOException {
    File file = new File("words.txt");
    Scanner sc = new Scanner(System.in);
    System.out.println("Enter a word you would like to search for:");
    String word = sc.nextLine();

    List<String> words = new ArrayList<>();

    try {
        sc = new Scanner(file).useDelimiter( ",");

        while (sc.hasNext()) {
            final String wordFromFile = sc.nextLine();
            if (wordFromFile.contains(word)) {
                // a match!
                System.out.println("The entered word: " + word  + " exists in the dictionary");
                break;
            }

        }
    } catch (IOException e) {
        System.out.println(" cannot write to file " + file.toString());
    }
}

}

Answer 1

只需遍历文件中的所有单词，首先将每个单词插入到文件中的HashSet中。这是线性时间O(n)完成，没有办法解决这个问题，因为你必须阅读整个文件。

假设文件中有一个单词，它就像：

HashSet<String> set = new HashSet<>();
while (sc.hasNext()) {
    set.add(sc.nextLine();
}

如果有人贴纸，他们真的希望它读取到列表类型集合，您可以从列表中生成这样的HashSet：

 Set<String> set = new HashSet<>(wordList);

注意：这个转换操作也是O(n)，所以要将它读入列表并转换为O(2n)，它仍然是O(n)，但是如果这个列表远远不是最优的

要查找和/或插入您检查的新单词，可以在O(1)时间执行此操作。

if (set.contains(word)) {
   //...blah..blah...bla...
} else {
   set.add(word);
}

因此，名称HashSet中的哈希。

Answer 2

这可能有助于您理解

public static void main(String a[]){
     File file = new File("words.txt");
     Scanner sc = new Scanner(System.in);
     System.out.println("Enter a word you would like to search for:");
     String word = sc.nextLine();

     boolean exist = false;
     List<String> words = new ArrayList<String>();
     sc = new Scanner(file);

     while(sc.hasNext()){

           words.add(sc.next());

     }
     for(int i=0;i<words.size();i++){
           if(words.get(i).equals(word)){
                   System.out.println("The entered word: " + word  + " exists in the dictionary");
                   exist = true;
                   break;
           }
     }
     if(!exist){
            System.out.println("This word is not in the dictionary.");
            System.out.println("Do you want to add it");
            if(System.in.read() == 'y'){
                   words.add(word);
            }
     }
}

Answer 3

如果您使用分隔符，则不应使用nextLine()。此外，如果你想添加一个元素到List使用.add(Object)

public static void main(String[] args) throws IOException {
    File file = new File("C:/Users/pelos.W2017/workspace/Frac/src/words.txt");
    Scanner sc = null;
    List<String> words = new ArrayList<>();

    try {
        sc = new Scanner(file);
        sc.useDelimiter(",");
        while (sc.hasNext()) 
            words.add(sc.next());
    } catch (IOException e) {
        System.out.println(" cannot write to file " + file.toString());
        return;
    }
    sc = new Scanner(System.in);

    boolean wordExists = false;
    String word = null;

    System.out.println("Enter a word you would like to search for:");
    word = sc.next();
    if (!words.contains(word)) {
        System.out.println("The entered word: " + word  + " doesn't exist in the dictionary");

        System.out.println("Add to list?");
        if(sc.next().equals("yes")){
            words.add(word);
        }
    }
    else{
        wordExists = true;
    }
    System.out.println("The entered word: " + word  + " exists in the dictionary");
}