Java替换方法问题

Question

我正在尝试为我的计算机科学类(class)做一个名为“加密/解密”的项目

代码如下

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

public class Tester { 
public static void main(String args[]) { 
    Scanner kbReader = new Scanner(System.in); 
    System.out.print("Enter a sentence that is to be encrypted: "); 
    String sntnc = kbReader.nextLine(); 
    System.out.println("Original Sentence = " + sntnc); 

    Crypto myCryptObj = new Crypto(); 
    String encryptdSntnc = myCryptObj.encrypt(sntnc); 
    System.out.println("Encrypted sentence = " + encryptdSntnc); 

    String decryptdSntnc = myCryptObj.decrypt(encryptdSntnc); 
    System.out.println("Decrypted sentence = " + decryptdSntnc); 
  } 
} 

class Crypto { 
 public String encrypt(String sntnc) { 
    sntnc = sntnc.replace("m", "ssad"); 
    sntnc = sntnc.replace("b", "dug>?/");
    sntnc = sntnc.replace("g", "jeb..w"); 
    sntnc = sntnc.replace("v", "ag',r"); 
    return sntnc; 
} 

public String decrypt(String sntnc) { 
    sntnc = sntnc.replace("ag',r", "v"); 
    sntnc = sntnc.replace("ssad", "m"); 
    sntnc = sntnc.replace("jeb..w", "g");  
    sntnc = sntnc.replace("dug>?/", "b"); 
    return sntnc; 
  } 
}

问题不在 Tester 类中，而是在 Crypto 类中。

输入是:这是一个非常重要的早晨。代码应该输出:

Enter a sentence that is to be encrypted: This is a very big morning.
Original Sentence: This is a very big morning.
Encrypted sentence: This is a ag',rery dug>?/ijeb..w ssadorninjeb..w.
Decrypted sentence: This is a very big morning.

但是加密句子行正在打印:

This is a ag',rery dujeb..w>?/ijeb..w ssadorninjeb..w.

sntnc.replace 方法正在替换已经替换的字母。我该如何修复它，使它不会两次替换东西？

Answer 1

问题来自于您替换字符串的逻辑:

sntnc = sntnc.replaceAll("b", "dug>?/");  // <-- replaces with a "g" here
sntnc = sntnc.replaceAll("g", "jeb..w");  // <-- so that "g" is also getting replaced here

一个简单的解决方案是使用 replaceAll 删除。通过重新排序 replaceAll 调用来使代码正常工作是非常脆弱的:您不知道将来有人会更改正在替换的内容并破坏所有内容。

通过迭代字符来构建字符串时，解决方案要简单得多。因为我们在构建字符串时有一个独特的临时容器，所以在替换时不会发生冲突。

public String encrypt(String sntnc) { 
     StringBuilder sb = new StringBuilder();
     for (char ch : sntnc.toCharArray()) {
         if (ch == 'm') sb.append("ssad");
         else if (ch == 'b') sb.append("dug>?/");
         else if (ch == 'g') sb.append("jeb..w");
         else if (ch == 'v') sb.append("ag',r");
         else sb.append(ch);
     }
     return sb.toString();
}