将FileWriter作为参数传递给方法 [英] Passing FileWriter as a parameter to a method

问题描述

我敢肯定，这个问题的答案很简单，所以我们开始吧.

I'm sure there is a fairly simple answer to this question, so here we go.

我正在尝试使用FileWriter将文本写入文件.我的程序从用户指定的现有文件中读取文本，然后询问是将文本打印到控制台还是新文件(也要由用户命名).

I'm trying to use a FileWriter to write text to a file. My program reads text in from an already existing file, specified by the user and then asks whether to print the text to the console or to a new file, also to be named by the user.

我相信我的问题是将FileWriter传递给"FileOrConsole"方法.我没有在"FileOrConsole"方法中正确传递或声明FileWriter吗?始终会创建该文件，但不会写入任何文件.

I believe my problem is with passing the FileWriter to the "FileOrConsole" method. Am I not passing or declaring the FileWriter in the "FileOrConsole" method correctly? The file is always created but nothing is written to it.

这是代码:

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

public class Reader {

public static void main(String[] args) throws IOException {
    Scanner s = null, input = new Scanner(System.in);
    BufferedWriter out = null;

    try {
        System.out.println("Would you like to read from a file?");
        String answer = input.nextLine();

        while (answer.startsWith("y")) {
            System.out.println("What file would you like to read from?");
            String file = input.nextLine();
            s = new Scanner(new BufferedReader(new FileReader(file)));

            System.out
                    .println("Would you like to print file output to console or file?");
            FileOrConsole(input.nextLine(), s, input, out);
            System.out
                    .println("\nWould you like to read from the file again?");
            answer = input.nextLine();
        }
        if (!answer.equalsIgnoreCase("yes")) {
            System.out.println("Goodbye!");
        }

    } catch (IOException e) {
        System.out.println("ERROR! File not found!");
        // e.printStackTrace();
    } finally {
        if (s != null) {
            s.close();
        }
        if (out != null) {
            out.close();
        }
    }
}

public static void FileOrConsole(String response, Scanner s, Scanner input,
        BufferedWriter out) {
    if (response.equalsIgnoreCase("console")) {
        while (s.hasNext()) {
            System.out.println(s.nextLine());
        }
    } else if (response.equalsIgnoreCase("file")) {
        System.out.println("Name of output file?");
        response = input.nextLine();
        try {
            out = new BufferedWriter(new FileWriter(response));
        } catch (IOException e) {
            e.printStackTrace();
        }
        while (s.hasNext()) {
            try {
                out.write(s.nextLine());
                out.newLine();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
        try {
            out.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    } else {
        System.out.println("Sorry, invalid response. File or console?");
        response = input.nextLine();
        FileOrConsole(response, s, input, out);
    }
  }
}

推荐答案

您会遇到经典错误，忘记了在Java中按值传递的参数是引用的值.事情是你的任务

you make classic error forgetting that parameters passed by value in case of java it is a value of the reference. The thing is that your assignment

out = new BufferedWriter(new FileWriter(response));

实际上不会更改main()中声明的变量，而是保持为空

actually does not change the variable declared in main() it stays null

BufferedWriter out = null; 然后最后它会通过if(out == null)跳过close() 因为它是缓冲的，所以您不执行刷新操作，不会将任何内容写入文件. 您要做的是out.close();在FileOrConsole方法调用旁边

BufferedWriter out = null; and then in finally it skips the close() by the if(out==null) and as it is Buffered and you do no flush nothing is written to file. what you got to do is out.close(); in side the FileOrConsole method call

OR

执行out = new BufferedWriter(new FileWriter(response)); 在它外面.您选择:-)

do the out = new BufferedWriter(new FileWriter(response)); outside of it. You choose :-)

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