用空格替换所有字母和等号

Question

我正在尝试使用此代码从包含随机数字和字母的文本文件中删除所有字母

package textEdit;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;

public class RemoveLetters {



    public static void readFile(String file) {
        try {
            FileReader fis = new FileReader(file);
            BufferedReader reader = new BufferedReader(fis);
            FileWriter writer = new FileWriter(file);
            BufferedWriter bwriter = new BufferedWriter(writer);
            String line = null;

            while ((line = reader.readLine()) != null) {
                for (int i = 0; i < symbolsAndLetters.length; i++) {
                    String str = symbolsAndLetters[i];
                    str = str.replace(str, ""); 
                }
            }
            reader.close();
            bwriter.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }   

    public static String[] symbolsAndLetters = {"A", "B", "C",
        "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", "d", "e", "f", "g", "h", "i", 
        "j", "k", "l", "m", "n", "o", "p", "q", "r", "s", "t",
        "u", "v", "w", "x", "y", "z",};

    /**
     * @param args
     */

    public static void main(String[] args) {
        readFile("c:/users/Kyle/workspace/Learn more java/src/music.txt");
    }

}

问题是，它会从文件中删除所有内容，我对 Java 读写非常陌生，所以谁能帮我弄清楚我做错了什么？

Answer 1

这是您在 while 循环中实际执行的操作（阅读 cmets）：

// iterating over the items of your own static array (without fast enumeration)
for (int i = 0; i < symbolsAndLetters.length; i++) {
    // initializing a new String and assigning it the value of your array
    // that is currently indexed in your for-loop
    String str = symbolsAndLetters[i];
    // replacing the String's content by replacing its value 
    // (1st parameter, the "str" value itself)
    // with an empty String
    str = str.replace(str, ""); 
}

这完全没有任何作用。

这就是你想要做的。

• 将您的编写器分配给一个新文件。之后您可以随时更换原件。
• 或者更好，只需使用 StringBuilder 并将原始内容替换为 关闭原始阅读器后，toString 表示 StringBuilder。
• 删除无用的“字符”String数组

• 像这样使用正则表达式：

  // your outer loop iterating over each line of your input file
  
  while ((line = reader.readLine()) != null) {
  
      // writing a new String representing the line read from the
      // original,
      // but replacing each of its alphabetic characters (through regex)
      // with an empty String
      writer.write(line.replaceAll("\\p{Alpha}", ""));
  }
  

Answer 2

我会创建一个新文件来写入输出。在这里，我只是在它后面加上“新”这个词。
-- FileWriter writer = new FileWriter(file + "new");

然后用正则表达式替换你想要的字符
-- line=line.replaceAll("[a-zA-Z]", "");

然后将其附加到新文件中：
-- bwriter.append(line +"\n");

Answer 3

在您的while 循环内，在for 循环之后，您应该将该行写回文件。

当循环进入下一行时，它会丢失str 中的所有内容。

您已经打开了文件输出流，但从不向其中写入任何内容。它不会覆盖所有内容，它不会写入任何内容。