Playing With the Letter ‘E’ in Java

The challenge

Given String str, return:

• If given String doesn’t contain any “e”, return: “There is no “e”.”
• If given String is empty, return empty String.
• If given String is `null`

The solution in Java code

Option 1:

public class WithoutLetterE {
  public static String findE(String str){
    if (str==null) return null;
    if (str.equals("")) return "";
    int len = str.length() - str.toLowerCase().replaceAll("e", "").length();
    if (len > 0) return String.valueOf(len);
    if (!str.contains("e")) return "There is no \"e\".";
    return null;
  }
}

Option 2:

public class WithoutLetterE {
  public static String findE(String str){
    if(str == null || str == "") return str;
    int i = str.replaceAll("[^eE]", "").length();
    return i == 0 ? "There is no \"e\"." : "" + i + "";
  }
}

Option 3:

public class WithoutLetterE {
    public static String findE(String str) {
        if (str == null) return null;
        int length = str.replaceAll("(?i)[^e]", "").length();
        return str.isEmpty() ? "" : length > 0 ? String.valueOf(length) : "There is no \"e\".";
    }
}

Test cases to validate our solution

import static org.junit.Assert.assertEquals;
import org.junit.Test;
public class WithoutLetterETest {
  @Test
  public void findE() {
    assertEquals("Should return \"There is no \"e\".\"", "There is no \"e\".", WithoutLetterE.findE("actual"));
    assertEquals("Should return \"1\"", "1", WithoutLetterE.findE("e"));
    assertEquals("Should return \"1\"", "1", WithoutLetterE.findE("English"));
    assertEquals("Should return \"4\"", "4", WithoutLetterE.findE("English exercise"));
    assertEquals("Should return \"\"", "", WithoutLetterE.findE(""));
    assertEquals("Should return null", null, WithoutLetterE.findE(null));
  }
}