Java无法通过3种方法创建文件 [英] java cannot create file by 3 methods

问题描述

我的活动目录中有一个test.txt.我需要创建三种方法:

I have a test.txt in my active directory.I need to create three methods:

1. 第一个必须创建一个输出文件并反转行的顺序.
2. 第二个单词
3. 第三个行和单词的顺序. test.txt包含输入.

1. First one has to create an output file and reverse the order of the lines.
2. Second the order of the words
3. The third the order of the lines and the words. test.txt contains the input.

我开发了每种方法都可以单独工作，但是以某种方式当我同时调用这三个方法时似乎不起作用. 我究竟做错了什么? 这是我的主要任务:

I developed every method to work on its own but somehow when I call all three at the same time it doesnt seem to work. What am i doing wrong? This is my main:

 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"));
 } }

这是我的课程.

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，已创建out1文件gest，这是我的第一种方法的输出文件，但为空.我没有得到用第二种方法创建的out2文件，并且out3很好. 我究竟做错了什么?错过了什么

When I run the program, out1 file gests created, which is the output file for my first method but it is empty. I don't get out2 file created by second method and out3 is fine. What am I doing wrong? What is missed

推荐答案

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

Add writer.flush(); before writer.close(); in all three methods

还有其他事情-扫描程序在构造函数中仅使用File初始化一次.它必须用其他方法重新初始化.

And other thing - Scanner is initialized with File only once in constructor. It has to be re-initialized in other methods.

sc =新的扫描仪(文件)； //扫描仪应该在所有三种方法中都可用

sc = new Scanner (file); // the scanner should be available in all three methods

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).由于到达文件末尾，以后的扫描程序不可用.

After running your code, output3.txt is generated (First method call). Later Scanner is not available since end of the file has been reached.

修复:接下来的两种方法应重新初始化扫描仪.

Fix : Scanner should be re-initialized for next two methods.

(使用您的聊天反馈更新答案)

1)由于您的限制，请创建三个扫描仪sc1，sc2和sc3.我建议使用正在处理的文件，以每种方法重新初始化扫描仪.

1) Create three scanners sc1,sc2 and sc3 due to your limitations. I would suggest to re-initialize the scanner in every method with the file being worked upon.

2)无需使用StringBuffer reverse()API即可以更简单的方式反转字符串(仅供学习)

2) String reversal in easier way without using StringBuffer reverse() API ( For learning purpose)

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

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