java - 如何打印不匹配的字符串

Question

我想打印不匹配的字符串，但结果为空。

public class Replacement  {
   public static void main(String[] ignored)  {

      String str = "aaa bbb ddd";
      Map<String, String> mapping = new HashMap<>();
      mapping.put("aaa", "hello");
      mapping.put("bbb", "java");
      mapping.put("ccc", "world");

      Pattern pattern = Pattern.compile("([a-zA-Z_]+)"); // pattern compiling
      Matcher matcher = pattern.matcher(str); // pattern matching

      StringBuffer sb = new StringBuffer();
      while(matcher.find())  { // while matcher found
         String replace = mapping.get(matcher.group());
         matcher.appendReplacement(sb, replace + " ");
      }
      matcher.appendTail(sb);

      System.out.println(sb);
  }
}

结果:

hello java null // I expected "hello java dddd

我需要放 while(!matcher.find())

Answer 1

为了实现你想要的，你需要检查替换是否存在，如果替换不存在则你需要附加 key 本身

     String replace = mapping.get(matcher.group());
     if(replace==null) {
         replace = matcher.group();
     }
     matcher.appendReplacement(sb, replace + " ");

希望这对您有所帮助。