为什么printwriter实际上没有写入文件？

Question

我一直在努力解决这个问题几个小时,我不确定如何最好地继续.

代码应该使用caesar密码读取一个文件,将其写入磁盘,并将其写入附加了_encoded的新文件.

它肯定会创建文件,但每次都是空白的.当我查看文档时,它说要确保刷新并关闭编剧.我做到了.

我也认为这可能是因为我正以迂回的方式接近这个问题; 我想知道是否使用了FileOutputstream.

        Scanner sc=new Scanner(inFile);
        //File outFile=new File("caesar_encoded.txt");

        //FileOutputStream outFileStream=new FileOutputStream(outFile);
        PrintWriter outStream=new PrintWriter("caesar_encoded.txt");

        while(sc.hasNext())
        {
            String phrase = sc.nextLine().toUpperCase();
    for (int i = 0; i < phrase.length(); i++) {
        if (Character.isLetter(phrase.charAt(i))) {
            for (int j = 0; j < alpha.length; j++) {
                if (phrase.charAt(i) == alpha[j]) {
                    if (j == alpha.length - 1) {
                        outStream.print(alpha[0]);
                    } else {
                        outStream.print(alpha[j + 1]);
                    }
                }
            }
        } else {
            outStream.print(phrase.charAt(i));
        }
    }
    outStream.println();
        }
        outStream.flush();
        outStream.close();

        sc.close();

我试过这样做,但结果相同:

Scanner sc=new Scanner(inFile);
 File outFile=new File("caesar_encoded.txt");
 FileOutputStream outFileStream=new FileOutputStream(outFile);
 PrintWriter outStream=new PrintWriter(outFileStream);

Answer 1

装饰它:

PrintWriter pw = new PrintWriter(new FileWriter("caesar_encoded.txt"), true);

或这个:

PrintStream ps = new PrintStream(new FileOutputStream("caesar_encoded.txt"), true);

当然,您了解Writer(字符流)和OutputStream(字节流)层次结构之间的区别.你通常不会越过这两个.您可以从跳跃OutputStream到Writer与OutputStreamWriter,但你不能走另一条路.

这段代码非常适合我.我接受了你的方法,猜测SHIFTED数组.在任何情况下,我都会在encrypted.txt文件中输出.我认为这是你的扫描仪问题.

package io;

import java.io.*;

/**
 * PrintWriterDemo
 * @author Michael
 * @link http://stackoverflow.com/questions/12849855/why-doesnt-printwriter-actually-write-to-the-file/12849867#comment17389040_12849867
 * @link http://en.wikipedia.org/wiki/Caesar_cipher
 * @since 10/11/12 7:17 PM
 */
public class PrintWriterDemo {

    public static void main(String[] args) {
        try {
            File unencrypted = new File((args.length > 0) ? args[0] : "resources/unencrypted.txt");
            File encrypted = new File((args.length > 1) ? args[1] : "resources/encrypted.txt");
            caesar(unencrypted, encrypted);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private static final char [] SHIFTED = { 
            'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 
            'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'A', 'B', 'C' };

    public static void caesar(File unencrypted, File encrypted) throws IOException {
        BufferedReader br = new BufferedReader(new FileReader(unencrypted));
        PrintWriter pw = new PrintWriter(encrypted);
        String line = "";
        while ((line = br.readLine()) != null) {
            String phrase =line.toUpperCase();
            for (int i = 0; i < phrase.length(); i++) {
                if (Character.isLetter(phrase.charAt(i))) {
                    for (int j = 0; j < SHIFTED.length; j++) {
                        if (phrase.charAt(i) == SHIFTED[j]) {
                            if (j == SHIFTED.length-1) {
                                pw.print(SHIFTED[0]);
                            } else {
                                pw.print(SHIFTED[j+1]);
                            }
                        }
                    }
                } else {
                    pw.print(phrase.charAt(i));
                }
            }
            pw.println();
        }
        pw.flush();
        pw.close();
        br.close();
    }
}

这是我的unencrypted.txt输入:

This should work out fine.
I have no idea what the problem is with the original code.
But I do know that this writes just fine.

这是我的encrypted.txt输出:

UIJT TIPVME XPSL PVU GJOF.
J IBWF OP JEFB XIBU UIF QSPCMFN JT XJUI UIF PSJHJOBM DPEF.
CVU J EP LOPX UIBU UIJT XSJUFT KVTU GJOF.