java - 寻找方法 RandomAccessFile

Question

我有一个任务，我需要显示 200 个随机字符，然后询问使用他们想要替换的字母，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了问题。有人可以帮助我朝着正确的方向前进吗？以下是我的一些其他问题:

• 我是否对 seek 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 < raf.length) 替换为具有以下内容的 while 循环:

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:现在文件是一个字符一个字符地遍历，而不是一个字节一个字节地遍历。考虑到各种字符编码可能不会为每个字符使用固定数量的字节，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

出于好奇，你到底想用什么来实现:

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