Codingbat前背部练习奇怪的结果

Question

public String frontBack(String str) { 
 if (str.length() > 1)
  {
   char first = str.charAt(0);
   char last = str.charAt(str.length()-1);
   String middle = str.substring(1,(str.length()-1));
   return last + first + middle;
  } 
 else 
   return str; 
 } 

                         Expected:       Run:       
 frontBack("code") →      "eodc"        "200od"      X      
 frontBack("a") →         "a"           "a"          OK     
 frontBack("ab") →        "ba"          "195"        X      
 frontBack("abc") →       "cba"         "196b"       X      
 frontBack("") →          ""            ""           OK     
 frontBack("Chocolate") → "ehocolatC"   "168hocolat" X    
 frontBack("aavJ") →      "Java"        "171av"      X      
 frontBack("hello") →     "oellh"       "215ell"     X     

Answer 1

Java假设您要对char执行整数加法，然后追加字符串。

要强制字符串连接，可以使用StringBuilder或类似的方法：

return "" + last + first + middle;

或

return new String(last + first + middle);