如何在JAVA中的文本文件中查找字符串

不久前，我尝试为一个项目做与这个问题非常相似的事情。在 Java 中有很多方法可以做到这一点，但我使用了 Scanner 类和 File 类。

public static void main(String[] args)
{
    Scanner input = new Scanner(System.in);      //Just a normal scanner

    System.out.println("Please enter in the pathname to the file you want to view.");
    String pathname = input.nextLine();          //Pathname to text file
    File book = new File(pathname);              //Creating a new file using the pathname

    if(book.canRead() == false)                  //If Java cant read the file, this will pop up
    {
        System.out.println("Your file cannot be read");
    }
    else if(book.canRead() == true)              //If Java can read the file, then this asks for the word to search for
    {
        System.out.println("Please enter in the word you wish to search for.");
        wordToSearchFor = input.nextLine();

        wordCounter(book);                        //Calls the method
  }

  System.out.println(wordToSearchFor.toLowerCase() + " appeared " + numOfOccurrences + " times in " + pathname);

}

这是您使用 File 类根据您提供的路径名创建文件的主要方法 EX - C:\Users\alex\Downloads\mobydick.txt 然后我检查您是否可以读取该文件，如果可以的话，我会调用一个方法来分析这本书本身

import java.io.*;
import java.util.Scanner;

public class TextReader
{
    private static int numOfOccurrences;         //Counter to keep track of the number of occurances
    private static String wordToSearchFor;       //String field so both methods can access it

    /*
    * This method takes in the file of the book so the scanner can look at it
    * and then does all of the calculating to see if the desired word appears,
    * and how many times it does appear if it does appear
    */

    public static void wordCounter(File bookInput)
    {
        try                                         
        {                                               
            Scanner bookAnalyzer = new Scanner(bookInput);     //Scanner for the book

            while(bookAnalyzer.hasNext())                      //While the scanner has something to look at next
            {
                String wordInLine = bookAnalyzer.next();        //Create a string for the next word

                wordInLine = wordInLine.toLowerCase();          //Make it lowercase
                String wordToSearchForLowerCase = wordToSearchFor.toLowerCase();
                String wordToSearchForLowerCasePeriod = wordToSearchForLowerCase + ".";

                if(wordInLine.indexOf(wordToSearchForLowerCase) != -1 && wordInLine.length() == wordToSearchFor.length())
                {
                    numOfOccurrences++;
                }
                else if(wordInLine.indexOf(wordToSearchForLowerCasePeriod) != -1 && wordInLine.length() == wordToSearchForLowerCasePeriod.length())
                {
                    numOfOccurrences++;
                }
            }
        }

        catch(FileNotFoundException e)               //Self explanitory
        {
            System.out.println("The error is FileNotFoundException - " + e);
            System.out.println("This should be impossible to get to because error checking is done before this step.");
        }
    }

Java中的扫描器可以拿一个File对象来分析，这是我在这个方法中做的第一件事。然后我使用一个 while 循环并询问扫描器是否在当前词之后有一个词。只要有一个字，这就会继续运行。然后我创建一个当前单词的字符串，扫描仪将其用作比较的参考。然后我使用 String 类附带的方法将所有内容变为小写，因为大写和小写字母都很重要。

此方法中的第一个 if 语句使用 String 类中的 indexOf 方法检查扫描器当前拥有的单词是否与您正在搜索的词匹配，该方法获取一些字符串并查看它是否存在于另一个字符串中。if 语句比较还确保所需的字长与书中的字长相同，以防您查找“the”并且它不会将“then”标记为单词，因为它包含“the”。第二个 if 语句做同样的事情，只是在你想要的单词末尾加上一个句点。如果您想加倍努力，您还可以检查感叹号、问号、逗号等，但我决定只检查句点。

每当其中一个 if 语句正确时，我将变量加 1，在扫描仪用完要搜索的单词后，我会打印出某个单词在文本文件中出现的总次数。