poking around

src/main/java/rocks/zipcode/quiz5/fundamentals/Calculator.java

@@ -1,5 +1,7 @@
 package rocks.zipcode.quiz5.fundamentals;
 
+import java.math.BigDecimal;
+
 /**
  * @author leon on 21/12/2018.
  */
@@ -27,8 +29,9 @@ public class Calculator {
     }
 
     public static Double add(Double value1, Double value2) {
-        return value1 + value2;
-        // return (Math.floor(value1 + value2) * 100) / 100;
+        String twoDecimals = String.format("%.2f", value1 + value2);
+
+        return Double.parseDouble(twoDecimals);
     }
 
     public static Double subtract(Double value1, Double value2) {

src/main/java/rocks/zipcode/quiz5/fundamentals/StringUtils.java

@@ -1,34 +1,84 @@
 package rocks.zipcode.quiz5.fundamentals;
 
+import java.util.*;
+
 /**
  * @author leon on 21/12/2018.
  */
 public class StringUtils {
     public static Character getMiddleCharacter(String string) {
-        return null;
+        return string.charAt(getMiddleIndex(string));
+    }
+
+    public static Integer getMiddleIndex(String string) {
+        return string.length() / 2;
     }
 
     public static String capitalizeMiddleCharacter(String str) {
-        return null;
+        StringBuilder builder = new StringBuilder(str);
+        builder.replace(getMiddleIndex(str), getMiddleIndex(str) + 1, getMiddleCharacter(str).toString().toUpperCase());
+
+        return builder.toString();
     }
 
     public static String lowerCaseMiddleCharacter(String str) {
-        return null;
+        StringBuilder builder = new StringBuilder(str);
+        builder.replace(getMiddleIndex(str), getMiddleIndex(str) + 1, getMiddleCharacter(str).toString().toLowerCase());
+
+        return builder.toString();
     }
 
     public static Boolean isIsogram(String str) {
-        return null;
+        List<Character> characters = new ArrayList<>();
+
+        for (int i = 0; i < str.length(); i++) {
+            if (!characters.contains(str.charAt(i))) {
+                characters.add(str.charAt(i));
+            } else {
+                return false;
+            }
+        }
+
+        return true;
     }
 
     public static Boolean hasDuplicateConsecutiveCharacters(String str) {
-        return null;
+        for (int i = 1; i < str.length(); i++) {
+            if (str.charAt(i) == str.charAt(i - 1)) {
+                return true;
+            }
+        }
+
+        return false;
     }
 
     public static String removeConsecutiveDuplicateCharacters(String str) {
-        return null;
+        Set<String> duplicateChars = new HashSet<>();
+
+        for (int i = 1; i < str.length(); i++) {
+            if (str.charAt(i) == str.charAt(i - 1)) {
+                duplicateChars.add(str.substring(i, i + 1));
+            }
+        }
+
+        for (String character : duplicateChars) {
+            str = str.replaceAll(character, "");
+        }
+
+        return str;
     }
 
     public static String invertCasing(String str) {
-        return null;
+        StringBuilder builder = new StringBuilder();
+
+        for (int i = 0; i < str.length(); i++) {
+            if (Character.isUpperCase(str.charAt(i))) {
+                builder.append(Character.toLowerCase(str.charAt(i)));
+            } else {
+                builder.append(Character.toUpperCase(str.charAt(i)));
+            }
+        }
+
+        return builder.toString();
     }
 }