java无法通过3种方法创建文件

Question

我的活动目录中有一个 test.txt。我需要创建三个方法：

1. 第一个必须创建一个输出文件并反转行的顺序。
2. 单词的第二个顺序
3. 第三行和单词的顺序。 test.txt 包含输入。

我开发了每种方法来独立工作，但不知何故，当我同时调用所有三个方法时，它似乎不起作用。 我究竟做错了什么？ 这是我的主要内容：

 import java.io.*;
  public class DemoReverser {
  public static void main (String [] args)
     throws IOException, FileNotFoundException {
     Reverser r = new Reverser(new File("test.txt"));
     r.completeReverse(new File("out3.txt"));
     r.reverseEachLine(new File("out2.txt"));
     r.reverseLines(new File("out1.txt"));
 } }

这是我的课。

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

public class Reverser {

Scanner sc = null ;
Scanner sc2 = null;

//constructor takes input file and initialize scanner sc pointing at input
public Reverser(File file)throws FileNotFoundException, IOException{

 sc = new Scanner (file); 
}

//this method reverses the order of the lines in the output
//prints to output file specified in argument.
public void reverseLines(File outpr)throws FileNotFoundException, IOException{

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

    while(sc.hasNextLine()){
        wordsarraylist.add(sc.nextLine());
        }

    Collections.reverse(wordsarraylist);

    FileWriter writer = new FileWriter(outpr,true); 

    for(String str: wordsarraylist) {
        writer.write(str+System.lineSeparator());
        }
    writer.flush();
    writer.close();
}




//this method reverses the order of the words in each line of the input
//and prints it to output file specified in argument.
public void reverseEachLine(File outpr)throws FileNotFoundException, IOException{

    while(sc.hasNextLine()){
        String sentence = sc.nextLine();
        String[] words = sentence.split(" ");
        ArrayList<String> wordsarraylist = new ArrayList<String>(Arrays.asList(words));
        Collections.reverse(wordsarraylist);
        FileWriter writer = new FileWriter(outpr,true); 

        for(String str: wordsarraylist) {
            writer.write(str + " ");
            }

        writer.write(System.lineSeparator());
        writer.flush();
        writer.close();
    }
 }

//this methhod reverses the order of the words in each sentence of the input
//then writes it to output file specified in argument
//then uses the output file as input and reverses the order of the sentences
//then overwrites the ouput file with the result
//the output file will contain the input sentences with their words reversed
// and the order of sentences reversed.
public void completeReverse(File outpr)  throws FileNotFoundException, IOException{

 while(sc.hasNextLine()){
        String sentence = sc.nextLine();
        String[] words = sentence.split(" ");
        ArrayList<String> wordsarraylist2 = new ArrayList<String>(Arrays.asList(words));
        Collections.reverse(wordsarraylist2);
        FileWriter writer = new FileWriter(outpr,true); 

        for(String str: wordsarraylist2) {
            writer.write(str + " ");
         }
         writer.write(System.lineSeparator());  
         writer.flush();
         writer.close();
    }

    sc2 = new Scanner (outpr);

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

    while(sc2.hasNextLine()){
        wordsarraylist.add(sc2.nextLine());
    }

    Collections.reverse(wordsarraylist);

    PrintWriter erase = new PrintWriter(outpr);
    erase.print("");
   // erase.flush();
    erase.close();

    FileWriter writer = new FileWriter(outpr,true); 

    for(String str: wordsarraylist) {
        writer.write(str+System.lineSeparator());
    }
    writer.flush();
    writer.close();





}

}

当我运行程序时，创建了 out1 文件，这是我第一个方法的输出文件，但它是空的。我没有得到由第二种方法创建的 out2 文件，而 out3 很好。 我究竟做错了什么？错过了什么

Answer 1

在所有三种方法中在writer.close(); 之前添加writer.flush();

还有其他的——扫描器在构造函数中只用文件初始化一次。必须用其他方法重新初始化。

sc = 新扫描仪（文件）； // 扫描器应该在所有三种方法中都可用

要捕获异常，请使用

try{
   // your code
}catch(Exception err){
   err.printStackTrace();
} 

运行代码后，将生成 output3.txt（第一个方法调用）。由于已到达文件末尾，因此稍后扫描仪不可用。

修复：扫描仪应该为接下来的两种方法重新初始化。

编辑：（使用您的聊天反馈更新答案）

1) 由于您的限制，创建三个扫描仪 sc1、sc2 和 sc3。我建议使用正在处理的文件在每种方法中重新初始化扫描仪。

2) 不使用 StringBuffer reverse() API 以更简单的方式反转字符串（用于学习目的）

int length = str.length();
  String reverse = "";
  for ( int i = length - 1 ; i >= 0 ; i-- ){
     reverse = reverse + str.charAt(i);
  }

Answer 2

如果您没有在当前尝试的地方写权限，这是可能的。所以你在测试的时候会报错。

但是，您在代码中犯了一些错误。 reverseEachLine 方法无效，您不应浪费代码来创建 completeReverse 方法。请注意以下事项。

• 在需要时构造Scanner
• 记得关闭Scanner
• 关闭Scanner后写入处理过的文件
• Filewriter 中不需要的删除追加
• 记得刷新FileWriter
• 确定方法之间的相似性和关系（完全反向是行反向和单词反向的组合）

公共类 MyReverser {

private File inputFile;

public MyReverser(File file) {
    this.inputFile = file;
}

public void reverseLines(File outpr) throws FileNotFoundException, IOException {
    Scanner sc = new java.util.Scanner(inputFile);
    List<String> wordsarraylist = new ArrayList<String>();
    while (sc.hasNextLine()) {
        wordsarraylist.add(sc.nextLine());
    }
    sc.close();

    Collections.reverse(wordsarraylist);

    FileWriter writer = new FileWriter(outpr, false);
    for (String str : wordsarraylist) {
        writer.write(str + System.lineSeparator());
    }
    writer.flush();
    writer.close();
}

public void reverseEachLine(File outpr) throws FileNotFoundException, IOException {
    Scanner sc = new Scanner(inputFile);

    ArrayList<List<String>> wordsarraylist = new ArrayList<List<String>>();
    while (sc.hasNextLine()) {
        String sentence = sc.nextLine();

        List words = Arrays.asList(sentence.split(" "));
        Collections.reverse(words);
        wordsarraylist.add(words);
    }

    FileWriter writer = new FileWriter(outpr, false);
    for (List<String> list : wordsarraylist) {
        for (String string : list) {
            writer.append(string + " ");
        }
        writer.append(System.lineSeparator());
    }
    writer.flush();
    writer.close();
}

public void completeReverse(File outpr) throws FileNotFoundException, IOException {
    //reverse lines first
    reverseLines(outpr);

    //then reverse words
    reverseEachLine(outpr);
}

}

Answer 3

这里的场景是扫描器是实例变量，一旦在您的一个操作方法中读取，当您从 Demo 类调用下一个方法时，它就不会再读取更多内容了。已进行更改以读取句子并将其存储在实例中，以便可以在每个方法中重复使用。

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

public class Reverser {

    Scanner sc = null;
    Scanner sc2 = null;

    boolean hasReadFile;
    List<String> fileLinesList;

    // constructor takes input file and initialize scanner sc pointing at input
    public Reverser(File file) throws FileNotFoundException, IOException {

        sc = new Scanner(file);
        hasReadFile = false;
        fileLinesList = new ArrayList<>();
    }

    // this method reverses the order of the lines in the output
    // prints to output file specified in argument.
    public void reverseLines(File outpr) throws FileNotFoundException,
            IOException {

        List<String> wordsarraylist = new ArrayList<String>();
        readFile();
        for (String sentence : fileLinesList) {
            wordsarraylist.add(sentence);
        }

        Collections.reverse(wordsarraylist);

        FileWriter writer = new FileWriter(outpr, true);

        for (String str : wordsarraylist) {
            writer.write(str + System.lineSeparator());
        }
        writer.flush();
        writer.close();
    }

    // this method reverses the order of the words in each line of the input
    // and prints it to output file specified in argument.
    public void reverseEachLine(File outpr) throws FileNotFoundException,
            IOException {
        readFile();
        for (String sentence : fileLinesList) {
            String[] words = sentence.split(" ");
            ArrayList<String> wordsarraylist = new ArrayList<String>(
                    Arrays.asList(words));
            Collections.reverse(wordsarraylist);
            FileWriter writer = new FileWriter(outpr, true);

            for (String str : wordsarraylist) {
                writer.write(str + " ");
            }

            writer.write(System.lineSeparator());
            writer.flush();
            writer.close();
        }
    }

    private void readFile() {
        if (!hasReadFile) {
            while (sc.hasNextLine()) {
                fileLinesList.add(sc.nextLine());
            }
            fileLinesList = Collections.unmodifiableList(fileLinesList);
            hasReadFile = true;
        }
    }

    // this methhod reverses the order of the words in each sentence of the
    // input
    // then writes it to output file specified in argument
    // then uses the output file as input and reverses the order of the
    // sentences
    // then overwrites the ouput file with the result
    // the output file will contain the input sentences with their words
    // reversed
    // and the order of sentences reversed.
    public void completeReverse(File outpr) throws FileNotFoundException,
            IOException {
        readFile();
        for (String sentence : fileLinesList) {
            String[] words = sentence.split(" ");
            ArrayList<String> wordsarraylist2 = new ArrayList<String>(
                    Arrays.asList(words));
            Collections.reverse(wordsarraylist2);
            FileWriter writer = new FileWriter(outpr, true);

            for (String str : wordsarraylist2) {
                writer.write(str + " ");
            }
            writer.write(System.lineSeparator());
            writer.flush();
            writer.close();
        }

        sc2 = new Scanner(outpr);

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

        while (sc2.hasNextLine()) {
            wordsarraylist.add(sc2.nextLine());
        }

        Collections.reverse(wordsarraylist);

        PrintWriter erase = new PrintWriter(outpr);
        erase.print("");
        // erase.flush();
        erase.close();

        FileWriter writer = new FileWriter(outpr, true);

        for (String str : wordsarraylist) {
            writer.write(str + System.lineSeparator());
        }
        writer.flush();
        writer.close();

    }
}