Java：用％20替換空格。爲什麼這打印先生％20 A而不是先生％20A

Question

嗨我試圖將字符串中的空間替換爲％20。 示例 輸入：Mr A 輸出：Mr％20A

我不明白爲什麼我的代碼打印「Mr％20 A」。我想打印「Mr％20A」，所以請告訴我該怎麼做？這裏是我的代碼：

import java.util.ArrayList; 
import java.util.Arrays; 
import java.util.List; 

public class TestAnswer { 



    public static void main(String[] args) { 
     //System.out.println(isPermutation("aXbcx", "xbcaX")); 
     System.out.println(URLify("Mr A")); 
    } 


    static String URLify(String s){ 
     StringBuilder sb = new StringBuilder(); 
     for(int i = 0; i < s.length(); i++){ 
      char c = s.charAt(i); 
      if(c == ' '){ 
       sb.append("%20"); 

      } 

      sb.append(c); 

     } 

     return sb.toString(); 
    } 

} 

Answer 1

你追加"%20"（在c == ' '情況下）之後，還追加c：

char c = s.charAt(i); 
if(c == ' '){ 
    sb.append("%20"); 
} 
sb.append(c); //here 

解決的辦法是追加c只有當它是不是' '。

解決方案：

char c = s.charAt(i); 
if(c == ' '){ 
    sb.append("%20"); 
}else{ 
    sb.append(c); 
} 

Answer 2

而是循環在String和使用StringBuilder重新創建的，請考慮使用這一行代碼：

s = s.replace(" ", "%20"); 

Answer 3

註釋掉

//System.out.println(isPermutation("aXbcx", "xbcaX")); 

我可以看到你正在解決中鼎

@sudo回答你的問題，我只是想提出一個更好的解決方案

您的解決方案可能是不夠好，但它是值得說明的是StringBuilder.append將增加一倍炭追加數組大小，將包含字符串每個如果容量不夠，直到它可以容納字符串

我的解決方案將迭代兩次在原來的字符串，但不會擴大返回的字符數組

private static char[] URLify(char[] original) { 
    char charToReplace = ' '; 
    char[] replacement = new char[]{'%', '2', '0'}; 
    // count charToReplace, in our case, count spaces 
    int numCharsToReplace = 0; 
    for (char c : original) if (c == charToReplace) numCharsToReplace++; 
    // creating new fixed char array to return 
    int resultSize = original.length + (numCharsToReplace * replacement.length) - numCharsToReplace; 
    char[] result = new char[resultSize]; 
    // we need two indexes,one to iterate the result char array, second to iterate the original 
    int i = 0, originalIdx = 0; 
    // until we set all new array of chars cells 
    while (i < resultSize) { 
     // get original character 
     char curOriginalChar = original[originalIdx]; 
     // this condition is first because I assume real URL will not contain as much spaces as chars 
     // if current character is not one we need to replace, copy 
     if (curOriginalChar != charToReplace) { 
      result[i] = curOriginalChar; 
      // for readable code the index incremented in new line 
      // could be replaced with "result[i++] = curOriginalChar;" 
      i++; 
     } 
     else { 
      for (char c : replacement) { 
       result[i] = c; 
       i++; 
      } 
     } 
     originalIdx++; 
    } 
    return result; 
} 

公用程序以獲取StringBuilder的實際字符數組長度

/** 
* StringBuilder's member "char value[]" is the character array stored inside StringBuilder, and it's 
* reference can be accessed only through getValue method, which is not public 
* so a little hack so we can know what is the char array size created 
*/ 
private static int getStringBuilderCharSize(StringBuilder sb) throws NoSuchFieldException, IllegalAccessException { 
    Field stringBuilderCharField = StringBuilder.class.getSuperclass().getDeclaredField("value"); 
    stringBuilderCharField.setAccessible(true); 
    char[] chars = (char[]) stringBuilderCharField.get(sb); 
    return chars.length; 
} 

用法舉例

public static void main(String[] args) throws NoSuchFieldException, IllegalAccessException { 
     String original = "Mr & Mrs Smith"; 
     char[] urlify = URLify(original.toCharArray()); 
     System.out.println(new String(urlify) + "|" + urlify.length); 

     StringBuilder sb = new StringBuilder(); 
     for (char c : original.toCharArray()) 
      if (c != ' ') sb.append(c); 
      else sb.append("%20"); 
     System.out.println(sb.toString() + "|" + getStringBuilderCharSize(sb)); 
    } 

輸出：

Mr%20&%20Mrs%20Smith|20 
Mr%20&%20Mrs%20Smith|34 

14細胞保存;）

Answer 4

在代碼中，你正在檢查如果一個字符是一個空格並且向StringBuilder附加一個「％20」。但是，if條件之後的sb.append（c）語句也會導致附加空間。 您可以在if內附加「％20」後添加continue關鍵字。

所以，你的代碼應該是這個樣子：

static String URLify(String s){ 
     StringBuilder sb = new StringBuilder(); 
     for(int i = 0; i < s.length(); i++){ 
      char c = s.charAt(i); 
      if(c == ' '){ 
       sb.append("%20"); 
       continue; 
      } 

      sb.append(c); 

     } 

     return sb.toString(); 
    }