check spelling and update topic

event-aggregator/README.md

@@ -9,6 +9,10 @@ tags:
  - Reactive
 ---
 
+## Name
+
+Event Aggregator
+
 ## Intent
 A system with lots of objects can lead to complexities when a
 client wants to subscribe to events. The client has to find and register for
@@ -17,6 +21,136 @@ requires a separate subscription. An Event Aggregator acts as a single source
 of events for many objects. It registers for all the events of the many objects
 allowing clients to register with just the aggregator.
 
+## Explanation
+
+Real-world example
+
+> King Joffrey sits on the iron throne and rules the seven kingdoms of Westeros. He receives most
+> of his critical information from King's Hand, the second in command. King's hand has many
+> close advisors himself, feeding him with relevant information about events occurring in the
+> kingdom.
+
+In Plain Words
+
+> Event Aggregator is an event mediator that collects events from multiple sources and delivers
+> them to registered observers.
+
+**Programmatic Example**
+
+In our programmatic example, we demonstrate the implementation of an event aggregator pattern. Some of
+the objects are event listeners, some are event emitters, and the event aggregator does both.
+
+```java
+public interface EventObserver {
+  void onEvent(Event e);
+}
+
+public abstract class EventEmitter {
+
+  private final Map<Event, List<EventObserver>> observerLists;
+
+  public EventEmitter() {
+    observerLists = new HashMap<>();
+  }
+
+  public final void registerObserver(EventObserver obs, Event e) {
+    ...
+  }
+
+  protected void notifyObservers(Event e) {
+    ...
+  }
+}
+```
+
+`KingJoffrey` is listening to events from `KingsHand`.
+
+```java
+@Slf4j
+public class KingJoffrey implements EventObserver {
+  @Override
+  public void onEvent(Event e) {
+    LOGGER.info("Received event from the King's Hand: {}", e.toString());
+  }
+}
+```
+
+`KingsHand` is listening to events from his subordinates `LordBaelish`, `LordVarys`, and `Scout`.
+Whatever he hears from them, he delivers to `KingJoffrey`.
+
+```java
+public class KingsHand extends EventEmitter implements EventObserver {
+
+  public KingsHand() {
+  }
+
+  public KingsHand(EventObserver obs, Event e) {
+    super(obs, e);
+  }
+
+  @Override
+  public void onEvent(Event e) {
+    notifyObservers(e);
+  }
+}
+```
+
+For example, `LordVarys` finds a traitor every Sunday and notifies the `KingsHand`.
+
+```java
+@Slf4j
+public class LordVarys extends EventEmitter implements EventObserver {
+  @Override
+  public void timePasses(Weekday day) {
+    if (day == Weekday.SATURDAY) {
+      notifyObservers(Event.TRAITOR_DETECTED);
+    }
+  }
+}
+```
+
+The following snippet demonstrates how the objects are constructed and wired together.
+
+```java
+    var kingJoffrey = new KingJoffrey();
+
+    var kingsHand = new KingsHand();
+    kingsHand.registerObserver(kingJoffrey, Event.TRAITOR_DETECTED);
+    kingsHand.registerObserver(kingJoffrey, Event.STARK_SIGHTED);
+    kingsHand.registerObserver(kingJoffrey, Event.WARSHIPS_APPROACHING);
+    kingsHand.registerObserver(kingJoffrey, Event.WHITE_WALKERS_SIGHTED);
+
+    var varys = new LordVarys();
+    varys.registerObserver(kingsHand, Event.TRAITOR_DETECTED);
+    varys.registerObserver(kingsHand, Event.WHITE_WALKERS_SIGHTED);
+
+    var scout = new Scout();
+    scout.registerObserver(kingsHand, Event.WARSHIPS_APPROACHING);
+    scout.registerObserver(varys, Event.WHITE_WALKERS_SIGHTED);
+
+    var baelish = new LordBaelish(kingsHand, Event.STARK_SIGHTED);
+
+    var emitters = List.of(
+        kingsHand,
+        baelish,
+        varys,
+        scout
+    );
+
+    Arrays.stream(Weekday.values())
+        .<Consumer<? super EventEmitter>>map(day -> emitter -> emitter.timePasses(day))
+        .forEachOrdered(emitters::forEach);
+```
+
+The console output after running the example.
+
+```
+18:21:52.955 [main] INFO com.iluwatar.event.aggregator.KingJoffrey - Received event from the King's Hand: Warships approaching
+18:21:52.960 [main] INFO com.iluwatar.event.aggregator.KingJoffrey - Received event from the King's Hand: White walkers sighted
+18:21:52.960 [main] INFO com.iluwatar.event.aggregator.KingJoffrey - Received event from the King's Hand: Stark sighted
+18:21:52.960 [main] INFO com.iluwatar.event.aggregator.KingJoffrey - Received event from the King's Hand: Traitor detected
+```
+
 ## Class diagram
 ![alt text](./etc/classes.png "Event Aggregator")
 
@@ -26,9 +160,13 @@ Use the Event Aggregator pattern when
 * Event Aggregator is a good choice when you have lots of objects that are
   potential event sources. Rather than have the observer deal with registering
   with them all, you can centralize the registration logic to the Event
-  Aggregator. As well as simplifying registration, a Event Aggregator also
+  Aggregator. As well as simplifying registration, an Event Aggregator also
   simplifies the memory management issues in using observers.
 
+## Related patterns
+
+* [Observer](https://java-design-patterns.com/patterns/observer/)
+
 ## Credits
 
 * [Martin Fowler - Event Aggregator](http://martinfowler.com/eaaDev/EventAggregator.html)

trampoline/README.md

@@ -17,19 +17,19 @@ and to interleave the execution of functions without hard coding them together.
 ## Explanation
 
 Recursion is a frequently adopted technique for solving algorithmic problems in a divide and conquer
-style. For example calculating fibonacci accumulating sum and factorials. In these kinds of problems 
-recursion is more straightforward than their loop counterpart. Furthermore recursion may need less 
-code and looks more concise. There is a saying that every recursion problem can be solved using 
-a loop with the cost of writing code that is more difficult to understand.
+style. For example, calculating Fibonacci accumulating sum and factorials. In these kinds of 
+problems, recursion is more straightforward than its loop counterpart. Furthermore, recursion may 
+need less code and looks more concise. There is a saying that every recursion problem can be solved 
+using a loop with the cost of writing code that is more difficult to understand.
 
-However recursion type solutions have one big caveat. For each recursive call it typically needs 
+However, recursion-type solutions have one big caveat. For each recursive call, it typically needs 
 an intermediate value stored and there is a limited amount of stack memory available. Running out of 
 stack memory creates a stack overflow error and halts the program execution.
 
-Trampoline pattern is a trick that allows us define recursive algorithms in Java without blowing the 
+Trampoline pattern is a trick that allows defining recursive algorithms in Java without blowing the 
 stack. 
 
-Real world example
+Real-world example
 
 > A recursive Fibonacci calculation without the stack overflow problem using the Trampoline pattern.       
 
@@ -105,24 +105,26 @@ public interface Trampoline<T> {
 Using the `Trampoline` to get Fibonacci values.
 
 ```java
-  public static Trampoline<Integer> loop(int times, int prod) {
+public static void main(String[] args) {
+    LOGGER.info("Start calculating war casualties");
+    var result = loop(10, 1).result();
+    LOGGER.info("The number of orcs perished in the war: {}", result);
+}
+
+public static Trampoline<Integer> loop(int times, int prod) {
     if (times == 0) {
         return Trampoline.done(prod);
     } else {
         return Trampoline.more(() -> loop(times - 1, prod * times));
     }
-  }
-  
-  log.info("start pattern");
-  var result = loop(10, 1).result();
-  log.info("result {}", result);
+}
 ```
 
 Program output:
 
 ```
-start pattern
-result 3628800
+19:22:24.462 [main] INFO com.iluwatar.trampoline.TrampolineApp - Start calculating war casualties
+19:22:24.472 [main] INFO com.iluwatar.trampoline.TrampolineApp - The number of orcs perished in the war: 3628800
 ```
 
 ## Class diagram
@@ -133,8 +135,8 @@ result 3628800
 
 Use the Trampoline pattern when
 
-* For implementing tail recursive function. This pattern allows to switch on a stackless operation.
-* For interleaving the execution of two or more functions on the same thread.
+* For implementing tail-recursive functions. This pattern allows to switch on a stackless operation.
+* For interleaving execution of two or more functions on the same thread.
 
 ## Known uses
 

trampoline/src/main/java/com/iluwatar/trampoline/Trampoline.java

@@ -107,6 +107,4 @@ public interface Trampoline<T> {
       }
     };
   }
-
-
 }

trampoline/src/main/java/com/iluwatar/trampoline/TrampolineApp.java

@@ -39,9 +39,9 @@ public class TrampolineApp {
    * Main program for showing pattern. It does loop with factorial function.
    */
   public static void main(String[] args) {
-    LOGGER.info("start pattern");
+    LOGGER.info("Start calculating war casualties");
     var result = loop(10, 1).result();
-    LOGGER.info("result {}", result);
+    LOGGER.info("The number of orcs perished in the war: {}", result);
 
   }
 
@@ -55,5 +55,4 @@ public class TrampolineApp {
       return Trampoline.more(() -> loop(times - 1, prod * times));
     }
   }
-
 }

unit-of-work/README.md

@@ -12,20 +12,20 @@ tags:
 
 ## Intent
 
-When a business transaction is completed, all the updates are sent as one big unit of work to be 
+When a business transaction is completed, all the the updates are sent as one big unit of work to be 
 persisted in one go to minimize database round-trips. 
 
 ## Explanation
 
-Real-world example
+Real world example
 
-> Arms dealer has a database containing weapon information. Merchants all over the town are 
-> constantly updating this information and it causes a high load on the database server. To make the 
+> We have a database containing student information. Administrators all over the country are 
+> constantly updating this information and it causes high load on the database server. To make the 
 > load more manageable we apply to Unit of Work pattern to send many small updates in batches.       
 
 In plain words
 
-> Unit of Work merges many small database updates in a single batch to optimize the number of 
+> Unit of Work merges many small database updates in single batch to optimize the number of 
 > round-trips. 
 
 [MartinFowler.com](https://martinfowler.com/eaaCatalog/unitOfWork.html) says
@@ -35,20 +35,37 @@ In plain words
 
 **Programmatic Example**
 
-Here's the `Weapon` entity that is being persisted in the database.
+Here's the `Student` entity that is being persisted to the database.
 
 ```java
-@Getter
-@RequiredArgsConstructor
-public class Weapon {
+public class Student {
   private final Integer id;
   private final String name;
+  private final String address;
+
+  public Student(Integer id, String name, String address) {
+    this.id = id;
+    this.name = name;
+    this.address = address;
+  }
+
+  public String getName() {
+    return name;
+  }
+
+  public Integer getId() {
+    return id;
+  }
+
+  public String getAddress() {
+    return address;
+  }
 }
 ```
 
-The essence of the implementation is the `ArmsDealer` implementing the Unit of Work pattern. 
+The essence of the implementation is the `StudentRepository` implementing the Unit of Work pattern. 
 It maintains a map of database operations (`context`) that need to be done and when `commit` is 
-called it applies them in a single batch.
+called it applies them in single batch.
 
 ```java
 public interface IUnitOfWork<T> {
@@ -67,117 +84,96 @@ public interface IUnitOfWork<T> {
 }
 
 @Slf4j
-@RequiredArgsConstructor
-public class ArmsDealer implements IUnitOfWork<Weapon> {
+public class StudentRepository implements IUnitOfWork<Student> {
 
-    private final Map<String, List<Weapon>> context;
-    private final WeaponDatabase weaponDatabase;
+  private final Map<String, List<Student>> context;
+  private final StudentDatabase studentDatabase;
 
-    @Override
-    public void registerNew(Weapon weapon) {
-        LOGGER.info("Registering {} for insert in context.", weapon.getName());
-        register(weapon, UnitActions.INSERT.getActionValue());
+  public StudentRepository(Map<String, List<Student>> context, StudentDatabase studentDatabase) {
+    this.context = context;
+    this.studentDatabase = studentDatabase;
   }
 
   @Override
-    public void registerModified(Weapon weapon) {
-        LOGGER.info("Registering {} for modify in context.", weapon.getName());
-        register(weapon, UnitActions.MODIFY.getActionValue());
+  public void registerNew(Student student) {
+    LOGGER.info("Registering {} for insert in context.", student.getName());
+    register(student, IUnitOfWork.INSERT);
+  }
+
+  @Override
+  public void registerModified(Student student) {
+    LOGGER.info("Registering {} for modify in context.", student.getName());
+    register(student, IUnitOfWork.MODIFY);
 
   }
 
   @Override
-    public void registerDeleted(Weapon weapon) {
-        LOGGER.info("Registering {} for delete in context.", weapon.getName());
-        register(weapon, UnitActions.DELETE.getActionValue());
+  public void registerDeleted(Student student) {
+    LOGGER.info("Registering {} for delete in context.", student.getName());
+    register(student, IUnitOfWork.DELETE);
   }
 
-    private void register(Weapon weapon, String operation) {
-        var weaponsToOperate = context.get(operation);
-        if (weaponsToOperate == null) {
-            weaponsToOperate = new ArrayList<>();
+  private void register(Student student, String operation) {
+    var studentsToOperate = context.get(operation);
+    if (studentsToOperate == null) {
+      studentsToOperate = new ArrayList<>();
     }
-        weaponsToOperate.add(weapon);
-        context.put(operation, weaponsToOperate);
+    studentsToOperate.add(student);
+    context.put(operation, studentsToOperate);
   }
 
-    /**
-     * All UnitOfWork operations are batched and executed together on commit only.
-     */
   @Override
   public void commit() {
     if (context == null || context.size() == 0) {
       return;
     }
     LOGGER.info("Commit started");
-        if (context.containsKey(UnitActions.INSERT.getActionValue())) {
+    if (context.containsKey(IUnitOfWork.INSERT)) {
       commitInsert();
     }
 
-        if (context.containsKey(UnitActions.MODIFY.getActionValue())) {
+    if (context.containsKey(IUnitOfWork.MODIFY)) {
       commitModify();
     }
-        if (context.containsKey(UnitActions.DELETE.getActionValue())) {
+    if (context.containsKey(IUnitOfWork.DELETE)) {
       commitDelete();
     }
     LOGGER.info("Commit finished.");
   }
 
   private void commitInsert() {
-        var weaponsToBeInserted = context.get(UnitActions.INSERT.getActionValue());
-        for (var weapon : weaponsToBeInserted) {
-            LOGGER.info("Inserting a new weapon {} to sales rack.", weapon.getName());
-            weaponDatabase.insert(weapon);
+    var studentsToBeInserted = context.get(IUnitOfWork.INSERT);
+    for (var student : studentsToBeInserted) {
+      LOGGER.info("Saving {} to database.", student.getName());
+      studentDatabase.insert(student);
     }
   }
 
   private void commitModify() {
-        var modifiedWeapons = context.get(UnitActions.MODIFY.getActionValue());
-        for (var weapon : modifiedWeapons) {
-            LOGGER.info("Scheduling {} for modification work.", weapon.getName());
-            weaponDatabase.modify(weapon);
+    var modifiedStudents = context.get(IUnitOfWork.MODIFY);
+    for (var student : modifiedStudents) {
+      LOGGER.info("Modifying {} to database.", student.getName());
+      studentDatabase.modify(student);
     }
   }
 
   private void commitDelete() {
-        var deletedWeapons = context.get(UnitActions.DELETE.getActionValue());
-        for (var weapon : deletedWeapons) {
-            LOGGER.info("Scrapping {}.", weapon.getName());
-            weaponDatabase.delete(weapon);
+    var deletedStudents = context.get(IUnitOfWork.DELETE);
+    for (var student : deletedStudents) {
+      LOGGER.info("Deleting {} to database.", student.getName());
+      studentDatabase.delete(student);
     }
   }
 }
 ```
 
-Here is how the whole app is put together.
+Finally, here's how we use the `StudentRepository` and `commit` the transaction.
 
 ```java
-// create some weapons
-var enchantedHammer = new Weapon(1, "enchanted hammer");
-var brokenGreatSword = new Weapon(2, "broken great sword");
-var silverTrident = new Weapon(3, "silver trident");
-
-// create repository
-var weaponRepository = new ArmsDealer(new HashMap<String, List<Weapon>>(), new WeaponDatabase());
-
-// perform operations on the weapons
-weaponRepository.registerNew(enchantedHammer);
-weaponRepository.registerModified(silverTrident);
-weaponRepository.registerDeleted(brokenGreatSword);
-weaponRepository.commit();
-```
-
-Here is the console output.
-
-```
-21:39:21.984 [main] INFO com.iluwatar.unitofwork.ArmsDealer - Registering enchanted hammer for insert in context.
-21:39:21.989 [main] INFO com.iluwatar.unitofwork.ArmsDealer - Registering silver trident for modify in context.
-21:39:21.989 [main] INFO com.iluwatar.unitofwork.ArmsDealer - Registering broken great sword for delete in context.
-21:39:21.989 [main] INFO com.iluwatar.unitofwork.ArmsDealer - Commit started
-21:39:21.989 [main] INFO com.iluwatar.unitofwork.ArmsDealer - Inserting a new weapon enchanted hammer to sales rack.
-21:39:21.989 [main] INFO com.iluwatar.unitofwork.ArmsDealer - Scheduling silver trident for modification work.
-21:39:21.989 [main] INFO com.iluwatar.unitofwork.ArmsDealer - Scrapping broken great sword.
-21:39:21.989 [main] INFO com.iluwatar.unitofwork.ArmsDealer - Commit finished.
+    studentRepository.registerNew(ram);
+    studentRepository.registerModified(shyam);
+    studentRepository.registerDeleted(gopi);
+    studentRepository.commit();
 ```
 
 ## Class diagram
@@ -190,7 +186,7 @@ Use the Unit Of Work pattern when
 
 * To optimize the time taken for database transactions.
 * To send changes to database as a unit of work which ensures atomicity of the transaction.
-* To reduce the number of database calls.
+* To reduce number of database calls.
 
 ## Tutorials
 

unit-of-work/etc/unit-of-work.ucls

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <class-diagram version="1.2.1" icons="true" always-add-relationships="false" generalizations="true" realizations="true" 
   associations="true" dependencies="false" nesting-relationships="true" router="FAN">  
-  <class id="1" language="java" name="com.iluwatar.unitofwork.WeaponDatabase" project="unit-of-work"
+  <class id="1" language="java" name="com.iluwatar.unitofwork.StudentDatabase" project="unit-of-work" 
     file="/unit-of-work/src/main/java/com/iluwatar/unitofwork/StudentDatabase.java" binary="false" corner="BOTTOM_RIGHT">    
     <position height="-1" width="-1" x="170" y="406"/>    
     <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
@@ -28,7 +28,7 @@
       <operations public="true" package="true" protected="true" private="true" static="true"/>    
     </display>  
   </class>  
-  <class id="4" language="java" name="com.iluwatar.unitofwork.ArmsDealer" project="unit-of-work"
+  <class id="4" language="java" name="com.iluwatar.unitofwork.StudentRepository" project="unit-of-work" 
     file="/unit-of-work/src/main/java/com/iluwatar/unitofwork/StudentRepository.java" binary="false" 
     corner="BOTTOM_RIGHT">    
     <position height="-1" width="-1" x="377" y="166"/>    
@@ -38,7 +38,7 @@
       <operations public="true" package="true" protected="true" private="true" static="true"/>    
     </display>  
   </class>  
-  <class id="5" language="java" name="com.iluwatar.unitofwork.Weapon" project="unit-of-work"
+  <class id="5" language="java" name="com.iluwatar.unitofwork.Student" project="unit-of-work" 
     file="/unit-of-work/src/main/java/com/iluwatar/unitofwork/Student.java" binary="false" corner="BOTTOM_RIGHT">    
     <position height="-1" width="-1" x="696" y="130"/>    
     <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 

unit-of-work/src/main/java/com/iluwatar/unitofwork/App.java

@@ -27,7 +27,7 @@ import java.util.HashMap;
 import java.util.List;
 
 /**
- * {@link App} Application demonstrating unit of work pattern.
+ * {@link App} Application for managing student data.
  */
 public class App {
   /**
@@ -37,19 +37,17 @@ public class App {
    */
 
   public static void main(String[] args) {
-    // create some weapons
-    var enchantedHammer = new Weapon(1, "enchanted hammer");
-    var brokenGreatSword = new Weapon(2, "broken great sword");
-    var silverTrident = new Weapon(3, "silver trident");
+    var ram = new Student(1, "Ram", "Street 9, Cupertino");
+    var shyam = new Student(2, "Shyam", "Z bridge, Pune");
+    var gopi = new Student(3, "Gopi", "Street 10, Mumbai");
 
-    // create repository
-    var weaponRepository = new ArmsDealer(new HashMap<String, List<Weapon>>(),
-            new WeaponDatabase());
+    var context = new HashMap<String, List<Student>>();
+    var studentDatabase = new StudentDatabase();
+    var studentRepository = new StudentRepository(context, studentDatabase);
 
-    // perform operations on the weapons
-    weaponRepository.registerNew(enchantedHammer);
-    weaponRepository.registerModified(silverTrident);
-    weaponRepository.registerDeleted(brokenGreatSword);
-    weaponRepository.commit();
+    studentRepository.registerNew(ram);
+    studentRepository.registerModified(shyam);
+    studentRepository.registerDeleted(gopi);
+    studentRepository.commit();
   }
 }

unit-of-work/src/main/java/com/iluwatar/unitofwork/Student.java

@@ -27,12 +27,14 @@ import lombok.Getter;
 import lombok.RequiredArgsConstructor;
 
 /**
- * {@link Weapon} is an entity.
+ * {@link Student} is an entity.
  */
 @Getter
 @RequiredArgsConstructor
-public class Weapon {
+public class Student {
 
   private final Integer id;
   private final String name;
+  private final String address;
+
 }

unit-of-work/src/main/java/com/iluwatar/unitofwork/StudentDatabase.java

@@ -24,19 +24,19 @@
 package com.iluwatar.unitofwork;
 
 /**
- * Act as database for weapon records.
+ * Act as Database for student records.
  */
-public class WeaponDatabase {
+public class StudentDatabase {
 
-  public void insert(Weapon weapon) {
+  public void insert(Student student) {
     //Some insert logic to DB
   }
 
-  public void modify(Weapon weapon) {
+  public void modify(Student student) {
     //Some modify logic to DB
   }
 
-  public void delete(Weapon weapon) {
+  public void delete(Student student) {
     //Some delete logic to DB
   }
 }

unit-of-work/src/main/java/com/iluwatar/unitofwork/StudentRepository.java

@@ -30,41 +30,41 @@ import lombok.RequiredArgsConstructor;
 import lombok.extern.slf4j.Slf4j;
 
 /**
- * {@link ArmsDealer} Weapon repository that supports unit of work for weapons.
+ * {@link StudentRepository} Student database repository. supports unit of work for student data.
  */
 @Slf4j
 @RequiredArgsConstructor
-public class ArmsDealer implements IUnitOfWork<Weapon> {
+public class StudentRepository implements IUnitOfWork<Student> {
 
-  private final Map<String, List<Weapon>> context;
-  private final WeaponDatabase weaponDatabase;
+  private final Map<String, List<Student>> context;
+  private final StudentDatabase studentDatabase;
 
   @Override
-  public void registerNew(Weapon weapon) {
-    LOGGER.info("Registering {} for insert in context.", weapon.getName());
-    register(weapon, UnitActions.INSERT.getActionValue());
+  public void registerNew(Student student) {
+    LOGGER.info("Registering {} for insert in context.", student.getName());
+    register(student, UnitActions.INSERT.getActionValue());
   }
 
   @Override
-  public void registerModified(Weapon weapon) {
-    LOGGER.info("Registering {} for modify in context.", weapon.getName());
-    register(weapon, UnitActions.MODIFY.getActionValue());
+  public void registerModified(Student student) {
+    LOGGER.info("Registering {} for modify in context.", student.getName());
+    register(student, UnitActions.MODIFY.getActionValue());
 
   }
 
   @Override
-  public void registerDeleted(Weapon weapon) {
-    LOGGER.info("Registering {} for delete in context.", weapon.getName());
-    register(weapon, UnitActions.DELETE.getActionValue());
+  public void registerDeleted(Student student) {
+    LOGGER.info("Registering {} for delete in context.", student.getName());
+    register(student, UnitActions.DELETE.getActionValue());
   }
 
-  private void register(Weapon weapon, String operation) {
-    var weaponsToOperate = context.get(operation);
-    if (weaponsToOperate == null) {
-      weaponsToOperate = new ArrayList<>();
+  private void register(Student student, String operation) {
+    var studentsToOperate = context.get(operation);
+    if (studentsToOperate == null) {
+      studentsToOperate = new ArrayList<>();
     }
-    weaponsToOperate.add(weapon);
-    context.put(operation, weaponsToOperate);
+    studentsToOperate.add(student);
+    context.put(operation, studentsToOperate);
   }
 
   /**
@@ -90,26 +90,26 @@ public class ArmsDealer implements IUnitOfWork<Weapon> {
   }
 
   private void commitInsert() {
-    var weaponsToBeInserted = context.get(UnitActions.INSERT.getActionValue());
-    for (var weapon : weaponsToBeInserted) {
-      LOGGER.info("Inserting a new weapon {} to sales rack.", weapon.getName());
-      weaponDatabase.insert(weapon);
+    var studentsToBeInserted = context.get(UnitActions.INSERT.getActionValue());
+    for (var student : studentsToBeInserted) {
+      LOGGER.info("Saving {} to database.", student.getName());
+      studentDatabase.insert(student);
     }
   }
 
   private void commitModify() {
-    var modifiedWeapons = context.get(UnitActions.MODIFY.getActionValue());
-    for (var weapon : modifiedWeapons) {
-      LOGGER.info("Scheduling {} for modification work.", weapon.getName());
-      weaponDatabase.modify(weapon);
+    var modifiedStudents = context.get(UnitActions.MODIFY.getActionValue());
+    for (var student : modifiedStudents) {
+      LOGGER.info("Modifying {} to database.", student.getName());
+      studentDatabase.modify(student);
     }
   }
 
   private void commitDelete() {
-    var deletedWeapons = context.get(UnitActions.DELETE.getActionValue());
-    for (var weapon : deletedWeapons) {
-      LOGGER.info("Scrapping {}.", weapon.getName());
-      weaponDatabase.delete(weapon);
+    var deletedStudents = context.get(UnitActions.DELETE.getActionValue());
+    for (var student : deletedStudents) {
+      LOGGER.info("Deleting {} to database.", student.getName());
+      studentDatabase.delete(student);
     }
   }
 }

unit-of-work/src/test/java/com/iluwatar/unitofwork/StudentRepositoryTest.java

@@ -36,102 +36,102 @@ import java.util.Map;
 import org.junit.jupiter.api.Test;
 
 /**
- * tests {@link ArmsDealer}
+ * tests {@link StudentRepository}
  */
 
-class ArmsDealerTest {
-  private final Weapon weapon1 = new Weapon(1, "battle ram");
-  private final Weapon weapon2 = new Weapon(1, "wooden lance");
+class StudentRepositoryTest {
+  private final Student student1 = new Student(1, "Ram", "street 9, cupertino");
+  private final Student student2 = new Student(1, "Sham", "Z bridge, pune");
 
-  private final Map<String, List<Weapon>> context = new HashMap<>();
-  private final WeaponDatabase weaponDatabase = mock(WeaponDatabase.class);
-  private final ArmsDealer armsDealer = new ArmsDealer(context, weaponDatabase);;
+  private final Map<String, List<Student>> context = new HashMap<>();
+  private final StudentDatabase studentDatabase = mock(StudentDatabase.class);
+  private final StudentRepository studentRepository = new StudentRepository(context, studentDatabase);;
 
   @Test
   void shouldSaveNewStudentWithoutWritingToDb() {
-    armsDealer.registerNew(weapon1);
-    armsDealer.registerNew(weapon2);
+    studentRepository.registerNew(student1);
+    studentRepository.registerNew(student2);
 
     assertEquals(2, context.get(UnitActions.INSERT.getActionValue()).size());
-    verifyNoMoreInteractions(weaponDatabase);
+    verifyNoMoreInteractions(studentDatabase);
   }
 
   @Test
   void shouldSaveDeletedStudentWithoutWritingToDb() {
-    armsDealer.registerDeleted(weapon1);
-    armsDealer.registerDeleted(weapon2);
+    studentRepository.registerDeleted(student1);
+    studentRepository.registerDeleted(student2);
 
     assertEquals(2, context.get(UnitActions.DELETE.getActionValue()).size());
-    verifyNoMoreInteractions(weaponDatabase);
+    verifyNoMoreInteractions(studentDatabase);
   }
 
   @Test
   void shouldSaveModifiedStudentWithoutWritingToDb() {
-    armsDealer.registerModified(weapon1);
-    armsDealer.registerModified(weapon2);
+    studentRepository.registerModified(student1);
+    studentRepository.registerModified(student2);
 
     assertEquals(2, context.get(UnitActions.MODIFY.getActionValue()).size());
-    verifyNoMoreInteractions(weaponDatabase);
+    verifyNoMoreInteractions(studentDatabase);
   }
 
   @Test
   void shouldSaveAllLocalChangesToDb() {
-    context.put(UnitActions.INSERT.getActionValue(), List.of(weapon1));
-    context.put(UnitActions.MODIFY.getActionValue(), List.of(weapon1));
-    context.put(UnitActions.DELETE.getActionValue(), List.of(weapon1));
+    context.put(UnitActions.INSERT.getActionValue(), List.of(student1));
+    context.put(UnitActions.MODIFY.getActionValue(), List.of(student1));
+    context.put(UnitActions.DELETE.getActionValue(), List.of(student1));
 
-    armsDealer.commit();
+    studentRepository.commit();
 
-    verify(weaponDatabase, times(1)).insert(weapon1);
-    verify(weaponDatabase, times(1)).modify(weapon1);
-    verify(weaponDatabase, times(1)).delete(weapon1);
+    verify(studentDatabase, times(1)).insert(student1);
+    verify(studentDatabase, times(1)).modify(student1);
+    verify(studentDatabase, times(1)).delete(student1);
   }
 
   @Test
   void shouldNotWriteToDbIfContextIsNull() {
-    var weaponRepository = new ArmsDealer(null, weaponDatabase);
+    var studentRepository = new StudentRepository(null, studentDatabase);
 
-    weaponRepository.commit();
+    studentRepository.commit();
 
-    verifyNoMoreInteractions(weaponDatabase);
+    verifyNoMoreInteractions(studentDatabase);
   }
 
   @Test
   void shouldNotWriteToDbIfNothingToCommit() {
-    var weaponRepository = new ArmsDealer(new HashMap<>(), weaponDatabase);
+    var studentRepository = new StudentRepository(new HashMap<>(), studentDatabase);
 
-    weaponRepository.commit();
+    studentRepository.commit();
 
-    verifyNoMoreInteractions(weaponDatabase);
+    verifyNoMoreInteractions(studentDatabase);
   }
 
   @Test
   void shouldNotInsertToDbIfNoRegisteredStudentsToBeCommitted() {
-    context.put(UnitActions.MODIFY.getActionValue(), List.of(weapon1));
-    context.put(UnitActions.DELETE.getActionValue(), List.of(weapon1));
+    context.put(UnitActions.MODIFY.getActionValue(), List.of(student1));
+    context.put(UnitActions.DELETE.getActionValue(), List.of(student1));
 
-    armsDealer.commit();
+    studentRepository.commit();
 
-    verify(weaponDatabase, never()).insert(weapon1);
+    verify(studentDatabase, never()).insert(student1);
   }
 
   @Test
   void shouldNotModifyToDbIfNotRegisteredStudentsToBeCommitted() {
-    context.put(UnitActions.INSERT.getActionValue(), List.of(weapon1));
-    context.put(UnitActions.DELETE.getActionValue(), List.of(weapon1));
+    context.put(UnitActions.INSERT.getActionValue(), List.of(student1));
+    context.put(UnitActions.DELETE.getActionValue(), List.of(student1));
 
-    armsDealer.commit();
+    studentRepository.commit();
 
-    verify(weaponDatabase, never()).modify(weapon1);
+    verify(studentDatabase, never()).modify(student1);
   }
 
   @Test
   void shouldNotDeleteFromDbIfNotRegisteredStudentsToBeCommitted() {
-    context.put(UnitActions.INSERT.getActionValue(), List.of(weapon1));
-    context.put(UnitActions.MODIFY.getActionValue(), List.of(weapon1));
+    context.put(UnitActions.INSERT.getActionValue(), List.of(student1));
+    context.put(UnitActions.MODIFY.getActionValue(), List.of(student1));
 
-    armsDealer.commit();
+    studentRepository.commit();
 
-    verify(weaponDatabase, never()).delete(weapon1);
+    verify(studentDatabase, never()).delete(student1);
   }
 }