diff --git a/.github/workflows/gradle.yml b/.github/workflows/gradle.yml
index 3f635f41..6631507a 100644
--- a/.github/workflows/gradle.yml
+++ b/.github/workflows/gradle.yml
@@ -4,6 +4,9 @@ on:
   push:
     branches:
       - Development
+  pull_request:
+    branches:
+      - Development
 
 jobs:
   test:
diff --git a/src/main/java/com/others/Ackermann.java b/src/main/java/com/others/Ackermann.java
new file mode 100644
index 00000000..a06cfaa6
--- /dev/null
+++ b/src/main/java/com/others/Ackermann.java
@@ -0,0 +1,34 @@
+package src.main.java.com.others;
+
+
+public class Ackermann {
+
+
+  /**
+   * Ackermann function - simplest and earliest-discovered examples of a total computable function
+   * that is not primitive recursive.
+   * 
+   * Defined only for NONNEGATIVE integers !!!
+   * 
+   * Time complexity is super-exponential. O(n(^))
+   * Any input m higher tahn (3,3) will result in StackOverflow
+   * @param m
+   * @param n
+   * @return
+   *
+   *
+   */
+  public long Ack(long m, long n) {
+
+    if (m == 0)
+      return n + 1;
+
+    if (n == 0)
+      return Ack(m - 1, 1);
+
+    return Ack(m - 1, Ack(m, n - 1));
+  }
+
+}
+
+
diff --git a/src/main/java/com/others/RoundRobin.java b/src/main/java/com/others/RoundRobin.java
new file mode 100644
index 00000000..b50cebeb
--- /dev/null
+++ b/src/main/java/com/others/RoundRobin.java
@@ -0,0 +1,141 @@
+package src.main.java.com.others;
+
+import java.util.ArrayList;
+
+/**
+ * This class implements the Round Robin Algorithm which is an cpu scheduling algorithm.
+ *
+ * @author George Giannios
+ */
+public class RoundRobin {
+    /**
+     * This method calculates the waiting time for all processes
+     *
+     * @param burstTime an array with burst time for all processes
+     * @param quantum   the quantum quantity
+     * @return an array with waiting time for all processes
+     */
+    public int[] calcWaitingTime(int[] burstTime, int quantum) {
+        int n = burstTime.length;
+        //create a copy of burstTime table to executeTime table
+        int[] executeTIme = new int[n];
+        for (int i = 0; i < n; i++) {
+            executeTIme[i] = burstTime[i];
+        }
+
+        //initialize the waiting time table and set all waiting times equal to zero
+        int[] waitingTime = new int[n];
+        for (int i = 0; i < n; i++) {
+            waitingTime[i] = 0;
+        }
+
+        //initialize an array list to emulate the queue of ready processes
+        ArrayList<Integer> readyQueue = new ArrayList<>();
+        for (int i = 0; i < n; i++) {
+            readyQueue.add(i);
+        }
+
+        //the total time that processes need to be finished
+        int time = 0;
+        int i = 0;
+        //calculate waiting times while there are uncompleted processes
+        while (!readyQueue.isEmpty()) {
+            //check if a process has finished
+            if (executeTIme[i] >= 0) {
+                if (executeTIme[i] - quantum > 0) {
+                    //add time that have been passed
+                    time += quantum;
+                    //this is the remaining burst time for the process i
+                    executeTIme[i] -= quantum;
+
+                } else if (executeTIme[i] - quantum == 0) {
+                    //add time that have been passed
+                    time += quantum;
+                    //calculate the total waiting time
+                    waitingTime[i] = time - burstTime[i];
+
+                    //mark the process as finished
+                    executeTIme[i] = -1;
+                    //remove the process that have finished by shrinking queue's length
+                    readyQueue.remove(readyQueue.size() - 1);
+
+                } else {
+                    //add time that have been passed
+                    time += executeTIme[i];
+                    //calculate the total waiting time
+                    waitingTime[i] = time - burstTime[i];
+
+                    //mark the process as finished
+                    executeTIme[i] = -1;
+                    //remove the process that have finished by shrinking queue's length
+                    readyQueue.remove(readyQueue.size() - 1);
+                }
+            }
+            i++;
+            if (i >= n) {
+                i = 0;
+            }
+        }
+
+        return waitingTime;
+    }
+
+
+    /**
+     * This method calculates turn around time for all processes
+     *
+     * @param burstTime   an array with burst time for all processes
+     * @param waitingTime an array with waiting time for all processes
+     * @return an array with turnaround time for all processes
+     */
+    public int[] calcTurnAroundTime(int[] burstTime, int[] waitingTime) {
+        int n = burstTime.length;
+        //initialize the turnaround time table
+        int[] turnAroundTime = new int[n];
+
+        //calculate turnaround time for each process (T.T= W.T + B.T)
+        for (int i = 0; i < n; i++) {
+            turnAroundTime[i] = waitingTime[i] + burstTime[i];
+        }
+
+        //return the turnaround time table
+        return turnAroundTime;
+    }
+
+
+    /**
+     * This method prints the results and calculates the average waiting and turnaround times
+     *
+     * @param burstTime an array with burst time for all processes
+     * @param quantum   the quantum quantity
+     */
+    void printAvgTimes(int[] burstTime, int quantum) {
+        int n = burstTime.length;
+        int totalWaitingTime = 0;
+        int totalTurnAroundTime = 0;
+
+        // Find waiting time of all processes
+        int[] waitingTime = calcWaitingTime(burstTime, quantum);
+
+        // Find turn around time for all processes
+        int[] turnAroundTime = calcTurnAroundTime(burstTime, waitingTime);
+
+        // Display processes along with all details
+        System.out.println("Process " + " Burst Time " +
+                " Waiting Time " + " Turnaround Time");
+        System.out.println("=======  ==========  ============  ===============");
+        // Calculate total waiting time and total turn around time
+        for (int i = 0; i < n; i++) {
+            totalWaitingTime += waitingTime[i];
+            totalTurnAroundTime += turnAroundTime[i];
+            System.out.println(i + "\t\t " + burstTime[i] + "\t\t\t " +
+                    waitingTime[i] + "\t\t\t   " + turnAroundTime[i]);
+        }
+
+        System.out.println("\nAverage waiting time = " +
+                (float) totalWaitingTime / (float) n);
+        System.out.println("Average turnaround time = " +
+                (float) totalTurnAroundTime / (float) n);
+    }
+}
+
diff --git a/src/main/java/com/string/Alphabetical.java b/src/main/java/com/string/Alphabetical.java
new file mode 100644
index 00000000..84b0f1c8
--- /dev/null
+++ b/src/main/java/com/string/Alphabetical.java
@@ -0,0 +1,20 @@
+package com.string;
+
+public class Alphabetical {
+
+    /**
+     * Check if a string is alphabetical order or not
+     *
+     * @param s a string
+     * @return {@code true} if given string is alphabetical order, otherwise {@code false}
+     */
+    public static boolean isAlphabetical(String s) {
+        s = s.toLowerCase();
+        for (int i = 0; i < s.length() - 1; ++i) {
+            if (!Character.isLetter(s.charAt(i)) || !(s.charAt(i) <= s.charAt(i + 1))) {
+                return false;
+            }
+        }
+        return true;
+    }
+}
diff --git a/src/main/java/com/string/Interleave.java b/src/main/java/com/string/Interleave.java
new file mode 100644
index 00000000..67a8311b
--- /dev/null
+++ b/src/main/java/com/string/Interleave.java
@@ -0,0 +1,151 @@
+package com.string;
+
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import static org.junit.Assert.assertEquals;
+
+public class Interleave {
+    @Test
+    public void testInterleaveRegularString() {
+        String string1 = "Hello";
+        String string2 = "World";
+        String expected = "HWeolrllod";
+        String actual = interleave(string1, string2);
+        assertEquals("Incorrect result from method.", expected, actual);
+    }
+
+    @Test
+    public void testInterleaveEmptyString() {
+        String string1 = "";
+        String string2 = "";
+        String string3 = "a";
+        String string4 = "abc";
+        String expected1 = "";
+        String actual1 = interleave(string1, string2);
+        String expected2 = "a";
+        String actual2 = interleave(string1, string3);
+        String expected3 = "abc";
+        String actual3 = interleave(string1, string4);
+        assertEquals("Incorrect result from method.", expected1, actual1);
+        assertEquals("Incorrect result from method.", expected2, actual2);
+        assertEquals("Incorrect result from method.", expected3, actual3);
+    }
+
+    @Test
+    public void testInterleaveSingleString() {
+        String string1 = "a";
+        String string2 = "b";
+        String expected = "ab";
+        String actual = interleave(string1, string2);
+        assertEquals("Incorrect result from method.", expected, actual);
+    }
+
+    @Test
+    public void testInterleaveIntString() {
+        String string1 = "1";
+        String string2 = "7";
+        String expected = "17";
+        String actual = interleave(string1, string2);
+        assertEquals("Incorrect result from method.", expected, actual);
+    }
+
+    @Test
+    public void testInterleaveMixedString() {
+        String string1 = "1a2b3c4d";
+        String string2 = "5e6f7g8h";
+        String expected = "15ae26bf37cg48dh";
+        String actual = interleave(string1, string2);
+        assertEquals("Incorrect result from method.", expected, actual);
+    }
+
+    @Test
+    public void testInterleaveSymbols() {
+        String string1 = "a@b%c/";
+        String string2 = "d#e$g%.";
+        String expected = "ad@#be%$cg/%.";
+        String actual = interleave(string1, string2);
+        assertEquals("Incorrect result from method.", expected, actual);
+    }
+
+    @Test
+    public void testInterleaveSpaces() {     // This string interleave algorithm defines a space as a valid character.
+        String string1 = " ";
+        String string2 = "a";
+        String string3 = "5 g";
+        String string4 = " 4 d ";
+        String expected1 = " a";
+        String actual1 = interleave(string1, string2);
+        String expected2 = "a5 g";
+        String actual2 = interleave(string2, string3);
+        String expected3 = "5  4g d ";
+        String actual3 = interleave(string3, string4);
+        assertEquals("Incorrect result from method.", expected1, actual1);
+        assertEquals("Incorrect result from method.", expected2, actual2);
+        assertEquals("Incorrect result from method.", expected3, actual3);
+    }
+
+    /**
+     * This method "interweaves" two input strings one character at a time. The first character of the
+     * first parameter string always starts the resulting string, unless that character is a space or is empty.
+     * This string interleaving method takes a space in a string (e.g. " ") into consideration.
+     *
+     * For example, if string1 = "abc" and string2 = "def", then the result would be "adbecf", as the first character
+     * of the string1 is 'a', then the first character of string2 is 'd', and so forth.
+     *
+     * For more information on interleaving, check out: https://en.wikipedia.org/wiki/Interleave_sequence
+     *
+     * @param string1
+     * @param string2
+     * @return string resulting from the interweaving of the two input strings; string1 and string2.
+     */
+    public String interleave(String string1, String string2) {
+        String result = "";     // The final interleaved string to return.
+        List<Character> list1 = new ArrayList<>();     // The ArrayList of string1, with each character being an individual element.
+        List<Character> list2 = new ArrayList<>();     // The ArrayList of string2, in a similar manner as above.
+
+        for (int i = 0; i < string1.length(); i++)     // Convert string1 into list1.
+            list1.add(string1.charAt(i));
+
+        for (int i = 0; i < string2.length(); i++)     // Convert string2 into list2.
+            list2.add(string2.charAt(i));
+
+        if (string1.length() == string2.length()) {     // Interleaving when string1 and string2 are equal length.
+            for (int j = 0; j < list1.size(); j++) {
+                result = result + list1.get(j);
+                result = result + list2.get(j);
+            }
+            return result;
+        }
+
+        if (string1.length() > string2.length()) {     // Interleaving when string1 is longer than string2.
+            while (list2.size() > 0) {
+                result = result + list1.get(0);
+                list1.remove(0);
+                result = result + list2.get(0);
+                list2.remove(0);
+            }
+            for (char character : list1) {     // Concatenate the rest of the characters in list1 to the result.
+                result = result + character;
+            }
+            return result;
+        }
+
+        if (string2.length() > string1.length()) {     // Interleaving when string2 is longer than string1.
+            while (list1.size() > 0) {
+                result = result + list1.get(0);
+                list1.remove(0);
+                result = result + list2.get(0);
+                list2.remove(0);
+            }
+            for (char character : list2) {     // Concatenate the rest of the characters in list2 to the result.
+                result = result + character;
+            }
+            return result;
+        }
+
+        return result;
+    }
+}
diff --git a/src/main/java/com/string/ReverseWords.java b/src/main/java/com/string/ReverseWords.java
new file mode 100644
index 00000000..9a4dec90
--- /dev/null
+++ b/src/main/java/com/string/ReverseWords.java
@@ -0,0 +1,30 @@
+package com.string;
+
+public class ReverseWords {
+  /**
+   * Converts all of the words in this {@code String} to reversed words
+   *
+   * @param s the string to convert
+   * @return the {@code String}, converted to a string with reveresed words.
+   */
+
+  public static String returnReverseWords(String s) {
+    StringBuilder sb = new StringBuilder();
+    StringBuilder word = new StringBuilder();
+
+    for(int i = 0; i < s.length(); i++) {
+        char c = s.charAt(i);
+        if(c == ' ') {
+          
+            sb.append(word);
+            sb.append(" ");
+            word.setLength(0);
+            continue;
+        }
+        word.insert(0, c);
+    }
+    sb.append(word);
+
+    return sb.toString();
+  }
+}
diff --git a/src/main/java/com/string/Upper.java b/src/main/java/com/string/Upper.java
new file mode 100644
index 00000000..87e2abe1
--- /dev/null
+++ b/src/main/java/com/string/Upper.java
@@ -0,0 +1,20 @@
+package com.string;
+
+public class Upper {
+
+    /**
+     * Converts all of the characters in this {@code String} to upper case
+     *
+     * @param s the string to convert
+     * @return the {@code String}, converted to uppercase.
+     */
+    public static String toUpperCase(String s) {
+        char[] values = s.toCharArray();
+        for (int i = 0; i < values.length; ++i) {
+            if (Character.isLetter(values[i]) && Character.isLowerCase(values[i])) {
+                values[i] = Character.toUpperCase(values[i]);
+            }
+        }
+        return new String(values);
+    }
+}
diff --git a/src/test/java/com/others/AckermannTest.java b/src/test/java/com/others/AckermannTest.java
new file mode 100644
index 00000000..c45b5542
--- /dev/null
+++ b/src/test/java/com/others/AckermannTest.java
@@ -0,0 +1,19 @@
+package src.test.java.com.others;
+
+import src.main.java.com.others.Ackermann;
+import static org.junit.Assert.assertEquals;
+import org.junit.Test;
+
+public class AckermannTest {
+
+  @Test
+  public void testAckermann() {
+    Ackermann ackTest = new Ackermann();
+    assertEquals("Error", 1, ackTest.Ack(0, 0));
+    assertEquals("Error", 3, ackTest.Ack(1, 1));
+    assertEquals("Error", 7, ackTest.Ack(2, 2));
+  }
+
+
+
+}
diff --git a/src/test/java/com/others/RoundRobinTest.java b/src/test/java/com/others/RoundRobinTest.java
new file mode 100644
index 00000000..b3fa8252
--- /dev/null
+++ b/src/test/java/com/others/RoundRobinTest.java
@@ -0,0 +1,26 @@
+package src.test.java.com.others;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+import src.main.java.com.others.RoundRobin;
+
+public class RoundRobinTest {
+    private final int[] burstTime = {5, 15, 4, 3};
+    private final RoundRobin roundRobin = new RoundRobin();
+
+    @Test
+    public void testWaitingTime() {
+        int[] expectedTime = {9, 12, 14, 9};
+        int[] realtime = roundRobin.calcWaitingTime(burstTime, 3);
+        Assert.assertArrayEquals(realtime, expectedTime);
+    }
+
+    @Test
+    public void testTurnAroundTIme() {
+        int[] expectedTIme = {14, 27, 18, 12};
+        int[] waitingTime = {9, 12, 14, 9};
+        int[] realTime = roundRobin.calcTurnAroundTime(burstTime, waitingTime);
+        Assert.assertArrayEquals(realTime, expectedTIme);
+    }
+}
diff --git a/src/test/java/com/string/AlphabeticalTest.java b/src/test/java/com/string/AlphabeticalTest.java
new file mode 100644
index 00000000..7291546a
--- /dev/null
+++ b/src/test/java/com/string/AlphabeticalTest.java
@@ -0,0 +1,13 @@
+package com.string;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+class AlphabeticalTest extends Alphabetical {
+
+    @Test
+    void testAlphabetical() {
+        Assertions.assertEquals(true, isAlphabetical("abc"), "The string is in order");
+        Assertions.assertEquals(false, isAlphabetical("testing"), "The string is not in order");
+    }
+}
\ No newline at end of file
diff --git a/src/test/java/com/string/ReverseWordsTest.java b/src/test/java/com/string/ReverseWordsTest.java
new file mode 100644
index 00000000..590c50f8
--- /dev/null
+++ b/src/test/java/com/string/ReverseWordsTest.java
@@ -0,0 +1,13 @@
+package com.string;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+class ReverseWordsTest extends ReverseWords {
+
+    @Test
+    void testReverseWords() {
+        Assertions.assertEquals(true, returnReverseWords("this is my car").equals("siht si ym rac"), "Correct");
+        Assertions.assertEquals(true, returnReverseWords("ABC 123").equals("CBA 321"), "Correct");
+    }
+}
\ No newline at end of file
diff --git a/src/test/java/com/string/UpperTest.java b/src/test/java/com/string/UpperTest.java
new file mode 100644
index 00000000..0f99b70d
--- /dev/null
+++ b/src/test/java/com/string/UpperTest.java
@@ -0,0 +1,15 @@
+package com.string;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+class UpperTest extends Upper {
+
+    @Test
+    void testUpper() {
+        Assertions.assertEquals(toUpperCase("abc"), ("abc").toUpperCase(), "The strings are equals");
+        //Assertions fail for functional reasons
+        Assertions.assertEquals(toUpperCase("abc"), "abc", "The strings are not equals");
+    }
+
+}
\ No newline at end of file