diff --git a/src/main/java/rocks/zipcode/quiz4/arrays/ArrayUtils.java b/src/main/java/rocks/zipcode/quiz4/arrays/ArrayUtils.java
index 6deaf61..8ee93ab 100644
--- a/src/main/java/rocks/zipcode/quiz4/arrays/ArrayUtils.java
+++ b/src/main/java/rocks/zipcode/quiz4/arrays/ArrayUtils.java
@@ -1,22 +1,36 @@
 package rocks.zipcode.quiz4.arrays;
 
+import java.util.ArrayList;
+import java.util.Arrays;
+
 /**
  * @author leon on 01/01/2019.
  */
 public class ArrayUtils {
     public static String getMiddleElement(String[] values) {
-        return null;
+        Integer midIndex = values.length / 2;
+        return values[midIndex];
     }
 
     public static String[] removeMiddleElement(String[] values) {
-        return null;
+        ArrayList<String> valuesList= new ArrayList<>(Arrays.asList(values));
+        valuesList.remove((values.length)/2);
+        String [] result = new String[valuesList.size()];
+        result = valuesList.toArray(result);
+        return result;
     }
 
     public static String getLastElement(String[] values) {
-        return null;
+        Integer lastIndex = values.length -1;
+        return values[lastIndex];
     }
 
     public static String[] removeLastElement(String[] values) {
-        return null;
+        ArrayList<String> valuesList = new ArrayList<>(Arrays.asList(values));
+        //Integer lastIndex = values.length -1;
+        valuesList.remove(values.length - 1);
+        String [] result = new String[valuesList.size()];
+        result = valuesList.toArray(result);
+        return result;
     }
 }
\ No newline at end of file
diff --git a/src/main/java/rocks/zipcode/quiz4/collections/WordCounter.java b/src/main/java/rocks/zipcode/quiz4/collections/WordCounter.java
index 2bf5ec2..290b44a 100644
--- a/src/main/java/rocks/zipcode/quiz4/collections/WordCounter.java
+++ b/src/main/java/rocks/zipcode/quiz4/collections/WordCounter.java
@@ -1,12 +1,34 @@
 package rocks.zipcode.quiz4.collections;
 
+import java.util.Arrays;
+import java.util.HashMap;
 import java.util.Map;
+import java.util.stream.Collector;
+import java.util.stream.Collectors;
 
 public class WordCounter {
+
+    Map<String, Long> wordCounts = new HashMap<>();
+    Map<String, Integer> newMap = new HashMap<>();
+
     public WordCounter(String... strings) {
+        wordCounts =
+                Arrays.stream(strings).collect(Collectors.groupingBy(w -> w, Collectors.counting()));
+        newMap = wordCounts.entrySet()
+                .stream()
+                .collect(Collectors.toMap(entry -> entry.getKey(), entry -> entry.getValue().intValue()));
     }
 
-    public Map<String, Integer> getWordCountMap() {
-        return null;
+    //Write method for using a loop also.
+//    HashMap<String,int> frequencymap = new HashMap<String,int>();
+//    foreach(String a in animals) {
+//        if(frequencymap.containsKey(a)) {
+//            frequencymap.put(a, frequencymap.get(a)+1);
+//        }
+//        else{ frequencymap.put(a, 1); }
+//    }
+
+    public Map<String, Integer> getWordCountMap(String... strings) {
+        return newMap;
     }
 }
diff --git a/src/main/java/rocks/zipcode/quiz4/collections/culonary/Curry.java b/src/main/java/rocks/zipcode/quiz4/collections/culonary/Curry.java
index 199cefc..96ce563 100644
--- a/src/main/java/rocks/zipcode/quiz4/collections/culonary/Curry.java
+++ b/src/main/java/rocks/zipcode/quiz4/collections/culonary/Curry.java
@@ -1,4 +1,4 @@
 package rocks.zipcode.quiz4.collections.culonary;
 
-public class Curry {
+public class Curry implements Spice{
 }
diff --git a/src/main/java/rocks/zipcode/quiz4/collections/culonary/Food.java b/src/main/java/rocks/zipcode/quiz4/collections/culonary/Food.java
index e06abbc..f414815 100644
--- a/src/main/java/rocks/zipcode/quiz4/collections/culonary/Food.java
+++ b/src/main/java/rocks/zipcode/quiz4/collections/culonary/Food.java
@@ -1,20 +1,48 @@
 package rocks.zipcode.quiz4.collections.culonary;
 
-import java.util.List;
-import java.util.Map;
+import java.util.*;
+import java.util.function.Function;
+import java.util.stream.Collectors;
 
 /**
  * @author leon on 27/12/2018.
  */
 public class Food {
+    List<Spice> mySpices = new ArrayList<>();
+    Set<Spice> spicesSet;
+
+
     public List<Spice> getAllSpices() {
-        return null;
+        return mySpices;
     }
 
     public <SpiceType extends Class<? extends Spice>> Map<SpiceType, Integer> getSpiceCount() {
-        return null;
+        //Map<SpiceType, Long> spiceMap = mySpices.stream().collect(Collectors.toMap((Spice)Collectors.groupingBy(Function.identity()), Collectors.counting()));
+
+        Map<SpiceType, Integer> spiceMap = new HashMap<>();
+        for (Spice spice: mySpices) {
+            SpiceType spiceType = (SpiceType) spice.getClass();
+            if(spiceMap.containsKey(spiceType)){
+                spiceMap.put(spiceType, spiceMap.get(spiceType) + 1);
+            }
+            else {
+                spiceMap.put(spiceType, 1);
+            }
+        }
+        return spiceMap;
     }
 
+    //    HashMap<String,int> frequencymap = new HashMap<String,int>();
+//    foreach(String a in animals) {
+//        if(frequencymap.containsKey(a)) {
+//            frequencymap.put(a, frequencymap.get(a)+1);
+//        }
+//        else{ frequencymap.put(a, 1); }
+//    }
+
+
     public void applySpice(Spice spice) {
+        mySpices.add(spice);
+        //spicesSet = new HashSet(mySpices);
     }
 }
diff --git a/src/main/java/rocks/zipcode/quiz4/collections/culonary/Ginger.java b/src/main/java/rocks/zipcode/quiz4/collections/culonary/Ginger.java
index 3c4e177..ef695be 100644
--- a/src/main/java/rocks/zipcode/quiz4/collections/culonary/Ginger.java
+++ b/src/main/java/rocks/zipcode/quiz4/collections/culonary/Ginger.java
@@ -3,5 +3,5 @@
 /**
  * @author leon on 27/12/2018.
  */
-public class Ginger {
+public class Ginger implements Spice{
 }
diff --git a/src/main/java/rocks/zipcode/quiz4/collections/culonary/Pepper.java b/src/main/java/rocks/zipcode/quiz4/collections/culonary/Pepper.java
index 4b771a8..248859f 100644
--- a/src/main/java/rocks/zipcode/quiz4/collections/culonary/Pepper.java
+++ b/src/main/java/rocks/zipcode/quiz4/collections/culonary/Pepper.java
@@ -3,5 +3,5 @@
 /**
  * @author leon on 27/12/2018.
  */
-public class Pepper {
+public class Pepper implements Spice{
 }
diff --git a/src/main/java/rocks/zipcode/quiz4/fundamentals/Calculator.java b/src/main/java/rocks/zipcode/quiz4/fundamentals/Calculator.java
index 02f2618..9660f04 100644
--- a/src/main/java/rocks/zipcode/quiz4/fundamentals/Calculator.java
+++ b/src/main/java/rocks/zipcode/quiz4/fundamentals/Calculator.java
@@ -4,32 +4,41 @@
  * @author leon on 21/12/2018.
  */
 public class Calculator {
+
     public static Double squareRoot(Double value) {
-        return null;
+        return Math.sqrt(value);
     }
 
     public static Double square(Double value) {
-        return null;
+        return value*value;
     }
 
     public static Double[] squareRoots(Double... value) {
-        return null;
+        Double [] valueRoots = new Double[value.length];
+        for (int i = 0; i < valueRoots.length; i++) {
+            valueRoots[i] = Math.sqrt(value[i]);
+        }
+        return valueRoots;
     }
 
     public static Double[] squares(Double... values) {
-        return null;
+        Double [] valueRoots = new Double[values.length];
+        for (int i = 0; i < valueRoots.length; i++) {
+            valueRoots[i] = values[i] * values[i];
+        }
+        return valueRoots;
     }
 
     public static Double add(Double value1, Double value2) {
-        return null;
+        return value1 + value2;
     }
 
     public static Double subtract(Double value1, Double value2) {
-        return null;
+        return value1 - value2;
     }
 
 
     public static Double divide(Double divisor, Double dividend) {
-        return null;
+        return divisor / dividend;
     }
 }
diff --git a/src/main/java/rocks/zipcode/quiz4/fundamentals/StringUtils.java b/src/main/java/rocks/zipcode/quiz4/fundamentals/StringUtils.java
index 5ec61be..b0b5c1c 100644
--- a/src/main/java/rocks/zipcode/quiz4/fundamentals/StringUtils.java
+++ b/src/main/java/rocks/zipcode/quiz4/fundamentals/StringUtils.java
@@ -1,34 +1,105 @@
 package rocks.zipcode.quiz4.fundamentals;
 
+import java.util.*;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
 /**
  * @author leon on 21/12/2018.
  */
 public class StringUtils {
     public static Character getMiddleCharacter(String string) {
-        return null;
+        char [] strArray = string.toCharArray();
+        return strArray[(string.length())/2];
     }
 
     public static String capitalizeMiddleCharacter(String str) {
-        return null;
+        String [] strArray = str.split("");
+        Integer midIndex = str.length()/2;
+        strArray[midIndex] = strArray[midIndex].toUpperCase();
+        return String.join("", strArray);
+        //Or using a stream: String joined = Arrays.stream(strArray).collect(Collectors.joining());
     }
 
     public static String lowerCaseMiddleCharacter(String str) {
-        return null;
+        String [] strArray = str.split("");
+        Integer midIndex = str.length()/2;
+        strArray[midIndex] = strArray[midIndex].toLowerCase();
+        String joined = Arrays.stream(strArray).collect(Collectors.joining());
+        return joined;
     }
 
     public static Boolean isIsogram(String str) {
-        return null;
+        Map<Character, Long> charMap = new HashMap<>();
+        char [] strArray = str.toCharArray();
+        Character [] nonPrimitiveArray = new Character[strArray.length];
+        for (int i = 0; i < nonPrimitiveArray.length; i++) {
+            nonPrimitiveArray[i] = (Character) strArray[i];
+        }
+        charMap = Arrays.stream(nonPrimitiveArray).collect(Collectors.groupingBy(c -> c, Collectors.counting()));
+        for (Long count : charMap.values()) {
+            if (count >= 2) {
+                return false;
+            }
+        }
+        return true;
     }
 
     public static Boolean hasDuplicateConsecutiveCharacters(String str) {
-        return null;
-    }
+
+
+        String[] strArray = str.split("");
+
+        if (strArray[str.length() -1].equals(str.length() - 2)){
+            return true;
+        }
+        for (int i = 0; i < str.length() - 2; i++) {
+            if (strArray[i].equals(strArray[i + 1])) {
+                return true;
+            }
+        }
+        return false;
+        }
+
 
     public static String removeConsecutiveDuplicateCharacters(String str) {
-        return null;
+        if(hasDuplicateConsecutiveCharacters(str)==true){
+
+            String[] strArray = str.split("");
+            StringBuilder sb = new StringBuilder();
+            for (int i = 0; i < str.length() - 2; i++) {
+                if (strArray[i].equals(strArray[i + 1])) {
+                    i=i+1;
+                } else if (!strArray[i].equals(strArray[i + 1])) {
+                    sb.append(strArray[i]);
+                }
+            }
+                if (!strArray[str.length() - 1].equals(str.length() - 2)) {
+                    sb.append(strArray[str.length() - 1]);
+                }
+                return sb.toString();
+        }
+        else { return str;}
     }
 
+
     public static String invertCasing(String str) {
-        return null;
+        StringBuilder sb = new StringBuilder(str);
+        char c;
+
+        for (int i = 0; i < str.length(); i++) {
+            c = str.charAt(i);
+            if (Character.isLowerCase(c))
+            {
+                sb.replace(i, i + 1, String.valueOf(Character.toUpperCase(c)));
+            }
+            else
+            {
+                sb.replace(i, i + 1, String.valueOf(Character.toLowerCase(c)));
+            }
+        }
+        return sb.toString();
     }
 }
\ No newline at end of file
diff --git a/src/main/java/rocks/zipcode/quiz4/objectorientation/account/Account.java b/src/main/java/rocks/zipcode/quiz4/objectorientation/account/Account.java
index 40eb4a8..7d0c98f 100644
--- a/src/main/java/rocks/zipcode/quiz4/objectorientation/account/Account.java
+++ b/src/main/java/rocks/zipcode/quiz4/objectorientation/account/Account.java
@@ -3,11 +3,20 @@
 /**
  * @author leon on 30/12/2018.
  */
-public class Account extends BankAccount {
+public class Account {
+    Long id;
+
+    public Account () {}
+
+    public Account(Long id) {
+        this.id = id;
+    }
+
     public Long getId() {
-        return null;
+        return id;
     }
 
     public void setId(Long id) {
+        this.id = id;
     }
 }
diff --git a/src/main/java/rocks/zipcode/quiz4/objectorientation/account/Bank.java b/src/main/java/rocks/zipcode/quiz4/objectorientation/account/Bank.java
index 0dd4183..df7151b 100644
--- a/src/main/java/rocks/zipcode/quiz4/objectorientation/account/Bank.java
+++ b/src/main/java/rocks/zipcode/quiz4/objectorientation/account/Bank.java
@@ -1,17 +1,25 @@
 package rocks.zipcode.quiz4.objectorientation.account;
 
+import java.util.ArrayList;
+
 /**
  * @author leon on 27/12/2018.
  */
 public class Bank {
-    public BankAccount removeBankAccountByIndex(Integer indexNumber) {
-        return null;
+    ArrayList<BankAccount> accountArrayList = new ArrayList<>(0);
+
+    public BankAccount removeBankAccountByIndex(Integer indexNumber) {  //returns BankAccount
+        BankAccount accountToRemove = accountArrayList.get(indexNumber);
+        this.accountArrayList.remove(accountToRemove);
+        return accountToRemove;
     }
 
     public void addBankAccount(BankAccount bankAccount) {
+        accountArrayList.add(bankAccount);
     }
 
     public Boolean containsBankAccount(BankAccount bankAccount) {
-        throw new UnsupportedOperationException("Method not yet implemented");
+        //throw new UnsupportedOperationException("Method not yet implemented");
+        return this.accountArrayList.contains(bankAccount);
     }
 }
diff --git a/src/main/java/rocks/zipcode/quiz4/objectorientation/account/BankAccount.java b/src/main/java/rocks/zipcode/quiz4/objectorientation/account/BankAccount.java
index 70ccb74..a4f053e 100644
--- a/src/main/java/rocks/zipcode/quiz4/objectorientation/account/BankAccount.java
+++ b/src/main/java/rocks/zipcode/quiz4/objectorientation/account/BankAccount.java
@@ -3,7 +3,44 @@
 /**
  * @author leon on 27/12/2018.
  */
-public class BankAccount {
+public class BankAccount extends Account implements Transactable {
+    Double balance;
+
+    public BankAccount () {
+        this.balance = 0.0;
+    }
+
+    public BankAccount(Double balance) {
+        this.balance = balance;
+    }
+
     public void setBalance(Double val) {
+        this.balance = val;
+    }
+
+    @Override
+    public void deposit(Double amountToIncreaseBy) throws IllegalArgumentException {
+        if (amountToIncreaseBy >= 0) {
+            balance = this.getBalance();
+            balance += amountToIncreaseBy;
+            setBalance(balance);
+        }
+        else throw new IllegalArgumentException();
+    }
+
+    @Override
+    public void withdrawal(Double amountToDecreaseBy) throws IllegalArgumentException{
+        balance = this.getBalance();
+        if (amountToDecreaseBy > balance || amountToDecreaseBy < 0) {
+            throw new IllegalArgumentException();
+        }
+        else {
+            balance -= amountToDecreaseBy;
+            this.setBalance(balance);
+        }
+    }
+
+    public Double getBalance() {
+        return balance;
     }
 }
diff --git a/src/main/java/rocks/zipcode/quiz4/objectorientation/account/Employee.java b/src/main/java/rocks/zipcode/quiz4/objectorientation/account/Employee.java
index 8407f1a..7ab125c 100644
--- a/src/main/java/rocks/zipcode/quiz4/objectorientation/account/Employee.java
+++ b/src/main/java/rocks/zipcode/quiz4/objectorientation/account/Employee.java
@@ -3,18 +3,96 @@
 /**
  * @author leon on 30/12/2018.
  */
-public class Employee {
+public class Employee implements Worker, Transactable {
+    BankAccount bankAccount;
+    Double hourlyWage;
+    Double moneyEarned;
+    Double hoursWorked;
+    Double balance;
+    Double bankAccountBalance;
+
+
     public Employee() {
+        hourlyWage = 35.0;
+        hoursWorked = 0.0;
+        balance = 0.0;
+        bankAccountBalance = 0.0;
+        bankAccount = new BankAccount();
     }
 
     public Employee(BankAccount bankAccount) {
+        this.bankAccount = bankAccount;
+        hourlyWage = 35.0;
+        hoursWorked = 0.0;
+        balance = 0.0;
+        bankAccountBalance = 0.0;
     }
 
     public BankAccount getBankAccount() {
-        return null;
+        //this.bankAccount.getBalance();
+        return bankAccount;
     }
 
     public void setBankAccount(BankAccount bankAccount) {
+        this.bankAccount = bankAccount;
+    }
+
+    public Employee(BankAccount bankAccount, Double hourlyWage, Double hoursWorked, Double moneyEarned,  Double balance) {
+        this.bankAccount = bankAccount;
+        this.hourlyWage = hourlyWage;
+        this.hoursWorked = hoursWorked;
+        this.moneyEarned = moneyEarned;
+        this.balance = balance;
+    }
+
+    @Override
+    public void deposit(Double amountToIncreaseBy) throws IllegalArgumentException{
+        if (amountToIncreaseBy < 0) {
+            throw new IllegalArgumentException ();
+        }
+        else {
+            balance = this.bankAccount.getBalance();
+            balance += amountToIncreaseBy;
+            bankAccount.setBalance(balance);
+        }
+    }
+
+    @Override
+    public void withdrawal(Double amountToDecreaseBy) throws IllegalArgumentException{
+        balance = this.bankAccount.getBalance();
+        System.out.println(balance);
+        if (amountToDecreaseBy > balance || amountToDecreaseBy < 0) {
+            throw new IllegalArgumentException();
+        }
+        else {
+            balance -= amountToDecreaseBy;
+            System.out.println(balance);
+            bankAccount.setBalance(balance);
+        }
+    }
+
+    @Override
+    public Double getBalance() {
+        return this.bankAccount.getBalance();
+    }
+
+    @Override
+    public void increaseHoursWorked(Double numberOfHours) {
+        this.hoursWorked += numberOfHours;
+    }
+
+    @Override
+    public Double getHoursWorked() {
+        return hoursWorked;
+    }
+
+    @Override
+    public Double getHourlyWage() {
+        return hourlyWage;
+    }
 
+    @Override
+    public Double getMoneyEarned() {
+        return moneyEarned;
     }
 }
diff --git a/src/main/java/rocks/zipcode/quiz4/objectorientation/account/Worker.java b/src/main/java/rocks/zipcode/quiz4/objectorientation/account/Worker.java
index 0f05f7e..1611283 100644
--- a/src/main/java/rocks/zipcode/quiz4/objectorientation/account/Worker.java
+++ b/src/main/java/rocks/zipcode/quiz4/objectorientation/account/Worker.java
@@ -8,4 +8,6 @@ public interface Worker {
     Double getHoursWorked();
     Double getHourlyWage();
     Double getMoneyEarned();
+    BankAccount getBankAccount();
+    void setBankAccount (BankAccount bankAccount);
 }