题目

定义toAlternatingCase 方法，使每个小写字母变为大写字母，每个大写字母变为小写字母。例如：

StringUtils.toAlternativeString("hello world") == "HELLO WORLD"
StringUtils.toAlternativeString("HELLO WORLD") == "hello world"
StringUtils.toAlternativeString("hello WORLD") == "HELLO world"
StringUtils.toAlternativeString("HeLLo WoRLD") == "hEllO wOrld"
StringUtils.toAlternativeString("12345") == "12345" // Non-alphabetical characters are unaffected
StringUtils.toAlternativeString("1a2b3c4d5e") == "1A2B3C4D5E"
StringUtils.toAlternativeString("StringUtils.toAlternatingCase") == "sTRINGuTILS.TOaLTERNATINGcASE"

像往常一样，你的方法不会使原始字符串产生变异。

测试用例：

import org.junit.Test;

import static org.junit.Assert.*;

public class StringUtilsTest {

  @Test
  public void fixedTests() {
    assertEquals("HELLO WORLD", StringUtils.toAlternativeString("hello world"));
    assertEquals("hello world", StringUtils.toAlternativeString("HELLO WORLD"));
    assertEquals("HELLO world", StringUtils.toAlternativeString("hello WORLD"));
    assertEquals("hEllO wOrld", StringUtils.toAlternativeString("HeLLo WoRLD"));
    assertEquals("Hello World", StringUtils.toAlternativeString(StringUtils.toAlternativeString("Hello World")));
    assertEquals("12345", StringUtils.toAlternativeString("12345"));
    assertEquals("1A2B3C4D5E", StringUtils.toAlternativeString("1a2b3c4d5e"));
    assertEquals("sTRINGuTILS.TOaLTERNATINGcASE", StringUtils.toAlternativeString("StringUtils.toAlternatingCase"));
  }
  
  @Test
  public void kataTitleTests() {
    assertEquals("ALTerNAtiNG CaSe", StringUtils.toAlternativeString("altERnaTIng cAsE"));
    assertEquals("altERnaTIng cAsE", StringUtils.toAlternativeString("ALTerNAtiNG CaSe"));
    assertEquals("ALTerNAtiNG CaSe <=> altERnaTIng cAsE", StringUtils.toAlternativeString("altERnaTIng cAsE <=> ALTerNAtiNG CaSe"));
    assertEquals("altERnaTIng cAsE <=> ALTerNAtiNG CaSe", StringUtils.toAlternativeString("ALTerNAtiNG CaSe <=> altERnaTIng cAsE"));
  }
}

解题

我的笨方法：

public class StringUtils {
  
  public static String toAlternativeString(String string) {
      char[] arr = string.toCharArray();
      for (int i =0;i<arr.length;i++) {
          if (arr[i] <= 90 && arr[i]  >= 65) {
              arr[i]  += 32;
          } else if (arr[i]  <= 122 && arr[i]  >= 97) {
              arr[i]  -= 32;
          }
      }
      return new String(arr);
  }
}

别人的：

public class StringUtils {
    public static String toAlternativeString(String string) {
        String result = "";
        for (char c : string.toCharArray()) {
            if(Character.isUpperCase(c)) {
                result += Character.toLowerCase(c);
            } else {
                result += Character.toUpperCase(c);
            }
        }
        return result;
    }
}

思考

看了别人的代码，(⊙o⊙)…官方库函数/方法积累不够，char封装类还有这么好的方法isUpperCase()。