阅读文本文件的每一行并将其与用户输入进行比较

Question

您好我正在编写一个程序，使用逐步细化和运行程序来读取顺序文本文件，或者1）插入2）修改或3）删除用户输入的条目。目前我的问题是我需要输入一个存在的字符串（如果它没有退出），然后将它与“输出”（或修改过的）字符串进行比较以修改它。

import java.io.*; 
import java.nio.file.*; 
import java.nio.charset.Charset; 
import java.nio.charset.StandardCharsets; 
import java.util.*; 
import java.util.Scanner; 

public class master2{ 
public static void main(String args[]) throws Exception 
{ 
    Scanner sc = new Scanner(System.in); 
    System.out.println("Enter 1.insertion into file 2.modify into file 3.delete in file"); 
    int choice=sc.nextInt(); 
    try 
    { 
     File newTextFile = new File("masterfile.txt"); 
     File temp = File.createTempFile("duplicateMaster", ".txt", newTextFile.getParentFile()); 
     String charset = "UTF-8"; 
     if(choice==1) 
     { 
      System.out.println("Enter String to insert"); 
      String str = sc.next(); 
      FileWriter fw = new FileWriter("masterfile.txt", true); 
      BufferedWriter bufferedWriter = new BufferedWriter(fw); 
      Scanner fileSC = new Scanner(newTextFile); 
      int count = 0; 
      while(fileSC.hasNextLine()) 
      { 
       String line = fileSC.nextLine(); 
       System.out.print("Line " + count + " "); 
       count++; 
       if (line.compareTo(str)==0) 
       { 
        System.out.println("Data already exists!"); 
        System.exit(0); 
       } 
      } 
      fw.append("\n" + str); 
      System.out.println("Entry added!"); 
      fw.close(); 
      fileSC.close(); 
      System.exit(0); 
     } 
     if(choice==2){ 
      Path path = Paths.get("masterfile.txt"); 
      String content = new String(Files.readAllBytes(path), StandardCharsets.UTF_8); 
      System.out.println("Enter String you want to modify which is present in text file"); 
      String input = sc.next(); 
      System.out.println("Enter new modified string"); 
      String output = sc.next(); 
      BufferedReader reader = new BufferedReader(new InputStreamReader(new FileInputStream(newTextFile), charset)); 
      PrintWriter writer = new PrintWriter(new OutputStreamWriter(new FileOutputStream(temp), charset)); 
      Scanner fileSC = new Scanner(newTextFile); 
      int count = 0; 
      while(fileSC.hasNextLine()) 
      { 
       String line = fileSC.nextLine(); 
       System.out.print("Line " + count + " "); 
       count++; 
       if (line.contains(input)) 
       { 
        content = line.replace(input, output); 
        writer.write(content); 
       } 
      } 
      newTextFile.delete(); 
      temp.renameTo(newTextFile); 
      System.out.print("Modified"); 
      reader.close(); 
      writer.close(); 
     } 
     if(choice==3) 
     { 
      String delete = "foo"; 
      System.out.println("Enter string to delete"); 
      delete = sc.nextLine(); 
      BufferedReader reader = new BufferedReader(new InputStreamReader(new FileInputStream(newTextFile), charset)); 
      PrintWriter writer = new PrintWriter(new OutputStreamWriter(new FileOutputStream(temp), charset)); 
      for (String line; (line = reader.readLine()) != null;) { 
       line = line.replace(delete, ""); 
       writer.println(line); 
       temp.renameTo(newTextFile); 
       temp.delete(); 

      } 
     } 
    }catch (Exception e) 
    { 
     System.out.println(e); 
    } 
    } 
} 

Answer 1

我发现了一些问题。

1）您需要为您的临时文件创建FileWriter，而不是masterfile.txt。

2）如果扫描仪的字符串与用户的输入不匹配，您仍然需要将其写入临时文件，事实上，您甚至不需要进行该比较，请让String.replace()为您做

while(fileSC.hasNextLine()) { 
    String line = fileSC.nextLine(); 
    System.out.print("Line " + count + " "); 
    count++; 
    line = line.replace(input, output); 
    bufferedWriter.write(line); 
} 

3）一旦找到匹配项，您就不能只是System.exit(0)。那文件的其余部分呢？另外，您应该关闭扫描仪和FileWriter。