Java Data Type - 如何计算字符串中字符的出现次数

import java.io.IOException;

public class Main {
  public static void main(String[] args) throws IOException {
    String input = "this is a test";
    StringBuilder result = new StringBuilder();
    char currentCharacter;
    int count;

    for (int i = 0; i < input.length(); i++) {
      currentCharacter = input.charAt(i);
      count = 1;
      while (i < input.length() - 1 && input.charAt(i + 1) == currentCharacter) {
        count++;
        i++;
      }
      result.append(currentCharacter);
      result.append(count);
    }

    System.out.println("" + result);
  }
}