查找方法随机访问文件

Question

我有一个作业，我需要显示 200 个随机字符，然后询问用户他们想要替换哪个字母，然后替换所有这些字母。我生成了随机字符，但在替换字母时遇到问题。有人可以帮助引导我朝着正确的方向前进吗？以下是我还有其他一些问题：

• 我是否对查找方法使用 for 循环，以便它找到所有这些字母？
• 我还需要显示每个字母的位置。我会使用文件指针吗，我也会把它放在一个循环中吗？

这是我的代码：

import java.io.*;
import java.util.Scanner;
public class Alphabet {
    public static char getRandomCharacter(char ch1, char ch2) {
        return (char) (ch1 + Math.random() * (ch2 - ch1 + 1));
    }
    public static char getRandomUpperCaseLetter() {
        return getRandomCharacter('A', 'Z');
    }
    public static void main(String[] args) throws IOException {
        try (RandomAccessFile raf = new RandomAccessFile("Alphabet.dat", "rw")) {
            raf.setLength(0);
            for (int row = 0; row < 10; ++row){
                for (int col = 0; col < 10; ++col) {
                    raf.writeChar(getRandomUpperCaseLetter());
                }
            }
            raf.seek(0);
            for (int row = 0; row < 10; ++row){
                for (int col = 0; col < 10; ++col) {
                    System.out.print(raf.readChar() +" ");
                }
                System.out.println();
            }
            Scanner Console = new Scanner(System.in);
            System.out.println("Current length of file is: "
                    + raf.length());
            System.out.print("Replace Characters: ");
            String letter = Console.next();
            System.out.print("With Character: ");
            String ch = Console.next();
                for(int j = 0; j < raf.length(); ++j){
                    raf.seek((raf.length()-1)*2);
                    raf.writeChars(ch);
                    System.out.print("Position" + raf.getFilePointer());
                }
            raf.writeChars(ch);
            raf.seek(0);
            for (int row = 0; row < 10; ++row){
                for (int col = 0; col < 10; ++col) {
                }
                System.out.println();
            }
        }
    }
}

Answer 1

尝试将 for-loop （j

long currPointer = 0;
while(currPointer < raf.length()) {
  long currPointer = raf.getFilePointer(); // save current cursor position
  char currentChar = raf.readChar(); // read current char
  if (currentChar == letter) { // if char equals that to be replaced
     raf.seek(currPointer); // step cursor one step back
     raf.writeChar(ch); // replace char
  }
  currPointer = raf.getFilePointer() // store the position of the cursor 
}

编辑：现在文件是逐个字符遍历的，而不是逐个字节遍历。鉴于各种字符编码可能不会使用每个字符的恒定字节数，这是最简单的方法。

基本上：

LOOP through all characters in file
    IF current character equals that to be replaced
         step cursor back by one (otherwise you'd be overwriting the next character)
         replace character

只是出于好奇，你到底想用什么来实现：

raf.seek((raf.length()-1)*2);