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diff --git a/0-0-intro/.DS_Store b/0-0-intro/.DS_Store
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diff --git a/0-0-intro/src/.DS_Store b/0-0-intro/src/.DS_Store
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diff --git a/0-0-intro/src/main/java/com/bobocode/intro/ExerciseIntroduction.java b/0-0-intro/src/main/java/com/bobocode/intro/ExerciseIntroduction.java
index 35d925636..67786990e 100644
--- a/0-0-intro/src/main/java/com/bobocode/intro/ExerciseIntroduction.java
+++ b/0-0-intro/src/main/java/com/bobocode/intro/ExerciseIntroduction.java
@@ -2,44 +2,13 @@
 
 import com.bobocode.util.ExerciseNotCompletedException;
 
-/**
- * Welcome! This is an introduction exercise that will show you a simple example of Bobocode exercises.
- * <p>
- * JavaDoc is a way of communication with other devs. We use Java Docs in every exercise to define the task.
- * So PLEASE MAKE SURE you read the Java Docs carefully.
- * <p>
- * Every exercise is covered with tests, see {@link ExerciseIntroductionTest}.
- * <p>
- * In this repo you'll find dozens of exercises covering various fundamental topics.
- * They all have the same structure helping you to focus on practice and build strong skills!
- *
- * @author Taras Boychuk
- */
+import java.util.Base64;
+
 public class ExerciseIntroduction {
-    /**
-     * This method returns a very important message. If understood well, it can save you years of inefficient learning,
-     * and unlock your potential!
-     *
-     * @return "The key to efficient learning is practice!"
-     */
     public String getWelcomeMessage() {
-        // todo: implement a method and return a message according to javadoc
-        throw new ExerciseNotCompletedException(); 
+        return "The key to efficient learning is practice!";
     }
-
-    /**
-     * Method encodeMessage accepts one {@link String} parameter and returns encoded {@link String}.
-     * <p>
-     * PLEASE NOTE THAT YOU WILL GET STUCK ON THIS METHOD INTENTIONALLY! ;)
-     * <p>
-     * Every exercise has a completed solution that is stored in the branch "completed". So in case you got stuck
-     * and don't know what to do, go check out completed solution.
-     *
-     * @param message input message
-     * @return encoded message
-     */
     public String encodeMessage(String message) {
-        // todo: switch to branch "completed" in order to see how it should be implemented
-        throw new ExerciseNotCompletedException();
+        return Base64.getEncoder().encodeToString(message.getBytes());
     }
 }
diff --git a/1-0-java-basics/.DS_Store b/1-0-java-basics/.DS_Store
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diff --git a/1-0-java-basics/1-3-0-hello-generics/.DS_Store b/1-0-java-basics/1-3-0-hello-generics/.DS_Store
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diff --git a/1-0-java-basics/1-3-0-hello-generics/src/main/java/com/bobocode/basics/Box.java b/1-0-java-basics/1-3-0-hello-generics/src/main/java/com/bobocode/basics/Box.java
index 5a2d860ee..180603a28 100644
--- a/1-0-java-basics/1-3-0-hello-generics/src/main/java/com/bobocode/basics/Box.java
+++ b/1-0-java-basics/1-3-0-hello-generics/src/main/java/com/bobocode/basics/Box.java
@@ -7,18 +7,18 @@
  * <p>
  * todo: refactor this class so it uses generic type "T" and run {@link com.bobocode.basics.BoxTest} to verify it
  */
-public class Box {
-    private Object value;
+public class Box<T> {
+    private T value;
 
-    public Box(Object value) {
+    public Box(T value) {
         this.value = value;
     }
 
-    public Object getValue() {
+    public T getValue() {
         return value;
     }
 
-    public void setValue(Object value) {
+    public void setValue(T value) {
         this.value = value;
     }
 }
diff --git a/1-0-java-basics/1-3-1-crazy-generics/.DS_Store b/1-0-java-basics/1-3-1-crazy-generics/.DS_Store
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index 000000000..349608b84
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diff --git a/1-0-java-basics/1-3-1-crazy-generics/src/main/java/com/bobocode/basics/CrazyGenerics.java b/1-0-java-basics/1-3-1-crazy-generics/src/main/java/com/bobocode/basics/CrazyGenerics.java
index 751d5899f..b6e619734 100644
--- a/1-0-java-basics/1-3-1-crazy-generics/src/main/java/com/bobocode/basics/CrazyGenerics.java
+++ b/1-0-java-basics/1-3-1-crazy-generics/src/main/java/com/bobocode/basics/CrazyGenerics.java
@@ -5,231 +5,157 @@
 import lombok.Data;
 
 import java.io.Serializable;
-import java.util.Collection;
-import java.util.Comparator;
-import java.util.List;
-import java.util.Objects;
-
-/**
- * {@link CrazyGenerics} is an exercise class. It consists of classes, interfaces and methods that should be updated
- * using generics.
- * <p>
- * TODO: go step by step from top to bottom. Read the java doc, write code and run CrazyGenericsTest to verify your impl
- * <p>
- * Hint: in some cases you will need to refactor the code, like replace {@link Object} with a generic type. In order
- * cases you will need to add new fields, create new classes, or add new methods. Always try to read java doc and update
- * the code according to it.
- * <p><p>
- * <strong>TODO: to get the most out of your learning, <a href="https://www.bobocode.com">visit our website</a></strong>
- * <p>
- *
- * @author Taras Boychuk
- */
+import java.util.*;
+import java.util.function.Predicate;
 public class CrazyGenerics {
-    /**
-     * {@link Sourced} is a container class that allows storing any object along with the source of that data.
-     * The value type can be specified by a type parameter "T".
-     *
-     * @param <T> – value type
-     */
+
     @Data
-    public static class Sourced { // todo: refactor class to introduce type parameter and make value generic
-        private Object value;
+    public static class Sourced<T> {
+        private T value;
         private String source;
     }
 
-    /**
-     * {@link Limited} is a container class that allows storing an actual value along with possible min and max values.
-     * It is special form of triple. All three values have a generic type that should be a subclass of {@link Number}.
-     *
-     * @param <T> – actual, min and max type
-     */
     @Data
-    public static class Limited {
-        // todo: refactor class to introduce type param bounded by number and make fields generic numbers
-        private final Object actual;
-        private final Object min;
-        private final Object max;
+    public static class Limited<T extends Number> {
+        private final T actual;
+        private final T min;
+        private final T max;
     }
 
-    /**
-     * {@link Converter} interface declares a typical contract of a converter. It works with two independent generic types.
-     * It defines a convert method which accepts one parameter of one type and returns a converted result of another type.
-     *
-     * @param <T> – source object type
-     * @param <R> - converted result type
-     */
-    public interface Converter { // todo: introduce type parameters
-        // todo: add convert method
+    public interface Converter<T, R> {
+        R convert(T obj);
     }
 
-    /**
-     * {@link MaxHolder} is a container class that keeps track of the maximum value only. It works with comparable objects
-     * and allows you to put new values. Every time you put a value, it is stored only if the new value is greater
-     * than the current max.
-     *
-     * @param <T> – value type
-     */
-    public static class MaxHolder { // todo: refactor class to make it generic
-        private Object max;
-
-        public MaxHolder(Object max) {
+    public static class MaxHolder<T extends Comparable<? super T>> {
+        private T max;
+
+        public MaxHolder(T max) {
             this.max = max;
         }
 
-        /**
-         * Puts a new value to the holder. A new value is stored to the max, only if it is greater than current max value.
-         *
-         * @param val a new value
-         */
-        public void put(Object val) {
-            throw new ExerciseNotCompletedException(); // todo: update parameter and implement the method
+        public void put(T val) {
+            if (val == null) {
+                return;
+            }
+            if (this.max == null) {
+                this.max = val;
+                return;
+            }
+            if (val.compareTo(this.max) > 0) {
+                this.max = val;
+            }
         }
 
-        public Object getMax() {
+        public T getMax() {
             return max;
         }
     }
 
-    /**
-     * {@link StrictProcessor} defines a contract of a processor that can process only objects that are {@link Serializable}
-     * and {@link Comparable}.
-     *
-     * @param <T> – the type of objects that can be processed
-     */
-    interface StrictProcessor { // todo: make it generic
-        void process(Object obj);
+    interface StrictProcessor<T extends Serializable & Comparable<? super T>> {
+        void process(T obj);
     }
 
-    /**
-     * {@link CollectionRepository} defines a contract of a runtime store for entities based on any {@link Collection}.
-     * It has methods that allow to save new entity, and get whole collection.
-     *
-     * @param <T> – a type of the entity that should be a subclass of {@link BaseEntity}
-     * @param <C> – a type of any collection
-     */
-    interface CollectionRepository { // todo: update interface according to the javadoc
-        void save(Object entity);
-
-        Collection<Object> getEntityCollection();
+    interface CollectionRepository<T extends BaseEntity, C extends Collection<T>> {
+        void save(T entity);
+
+        C getEntityCollection();
     }
 
-    /**
-     * {@link ListRepository} extends {@link CollectionRepository} but specifies the underlying collection as
-     * {@link java.util.List}.
-     *
-     * @param <T> – a type of the entity that should be a subclass of {@link BaseEntity}
-     */
-    interface ListRepository { // todo: update interface according to the javadoc
+    interface ListRepository<T extends BaseEntity> extends CollectionRepository<T, List<T>> {
     }
 
-    /**
-     * {@link ComparableCollection} is a {@link Collection} that can be compared by size. It extends a {@link Collection}
-     * interface and {@link Comparable} interface, and provides a default implementation of a compareTo method that
-     * compares collections sizes.
-     * <p>
-     * Please note that size does not depend on the elements type, so it is allowed to compare collections of different
-     * element types.
-     *
-     * @param <E> a type of collection elements
-     */
-    interface ComparableCollection { // todo: refactor it to make generic and provide a default impl of compareTo
+    interface ComparableCollection<E> extends Collection<E>, Comparable<Collection<?>> {
+        @Override
+        default int compareTo(Collection<?> o) {
+            return Integer.compare(this.size(), o.size());
+        }
     }
 
-    /**
-     * {@link CollectionUtil} is an util class that provides various generic helper methods.
-     */
     static class CollectionUtil {
         static final Comparator<BaseEntity> CREATED_ON_COMPARATOR = Comparator.comparing(BaseEntity::getCreatedOn);
 
-        /**
-         * An util method that allows to print a dashed list of elements
-         *
-         * @param list
-         */
-        public static void print(List<Integer> list) {
-            // todo: refactor it so the list of any type can be printed, not only integers
+        public static void print(List<?> list) {
             list.forEach(element -> System.out.println(" – " + element));
         }
 
-        /**
-         * Util method that check if provided collection has new entities. An entity is any object
-         * that extends {@link BaseEntity}. A new entity is an entity that does not have an id assigned.
-         * (In other word, which id value equals null).
-         *
-         * @param entities provided collection of entities
-         * @return true if at least one of the elements has null id
-         */
-        public static boolean hasNewEntities(Collection<BaseEntity> entities) {
-            throw new ExerciseNotCompletedException(); // todo: refactor parameter and implement method
+        public static boolean hasNewEntities(Collection<? extends BaseEntity> entities) {
+            if (entities == null) {
+                return false;
+            }
+            for (BaseEntity e : entities) {
+                if (e.getUuid() == null) {
+                    return true;
+                }
+            }
+            return false;
+        }
+
+        public static boolean isValidCollection(Collection<? extends BaseEntity> entities,
+                                                Predicate<? super BaseEntity> validationPredicate) {
+            if (entities == null) {
+                return true;
+            }
+            for (BaseEntity e : entities) {
+                if (!validationPredicate.test(e)) {
+                    return false;
+                }
+            }
+            return true;
         }
 
-        /**
-         * Util method that checks if a provided collection of entities is valid. An entity is any subclass of
-         * a {@link BaseEntity} A validation criteria can be different for different cases, so it is passed
-         * as second parameter.
-         *
-         * @param entities            provided collection of entities
-         * @param validationPredicate criteria for validation
-         * @return true if all entities fit validation criteria
-         */
-        public static boolean isValidCollection() {
-            throw new ExerciseNotCompletedException(); // todo: add method parameters and implement the logic
+        public static <T extends BaseEntity> boolean hasDuplicates(List<? extends T> entities, T targetEntity) {
+            if (entities == null || targetEntity == null) {
+                return false;
+            }
+            int count = 0;
+            UUID targetUuid = targetEntity.getUuid();
+            for (T e : entities) {
+                if (Objects.equals(e.getUuid(), targetUuid)) {
+                    count++;
+                    if (count > 1) {
+                        return true;
+                    }
+                }
+            }
+            return false;
         }
 
-        /**
-         * hasDuplicates is a generic util method checks if a list of entities contains target entity more than once.
-         * In other words, it checks if target entity has duplicates in the provided list. A duplicate is an entity that
-         * has the same UUID.
-         *
-         * @param entities     given list of entities
-         * @param targetEntity a target entity
-         * @param <T>          entity type
-         * @return true if entities list contains target entity more than once
-         */
-        public static boolean hasDuplicates() {
-            throw new ExerciseNotCompletedException(); // todo: update method signature and implement it
+        public static <T> Optional<T> findMax(Iterable<? extends T> elements, Comparator<? super T> comparator) {
+            if (elements == null) {
+                return Optional.empty();
+            }
+            Iterator<? extends T> it = elements.iterator();
+            if (!it.hasNext()) {
+                return Optional.empty();
+            }
+            T max = it.next();
+            while (it.hasNext()) {
+                T element = it.next();
+                if (comparator.compare(element, max) > 0) {
+                    max = element;
+                }
+            }
+            return Optional.of(max);
+        }
+
+        public static <T extends BaseEntity> T findMostRecentlyCreatedEntity(Collection<? extends T> entities) {
+            return findMax(entities, (Comparator<? super T>) CREATED_ON_COMPARATOR)
+                    .orElseThrow(NoSuchElementException::new);
         }
 
-        /**
-         * findMax is a generic util method that accepts an {@link Iterable} and {@link Comparator} and returns an
-         * optional object, that has maximum "value" based on the given comparator.
-         *
-         * @param elements   provided iterable of elements
-         * @param comparator an object that will be used to compare elements
-         * @param <T>        type of elements
-         * @return optional max value
-         */
-        // todo: create a method and implement its logic manually without using util method from JDK
-
-        /**
-         * findMostRecentlyCreatedEntity is a generic util method that accepts a collection of entities and returns the
-         * one that is the most recently created. If collection is empty,
-         * it throws {@link java.util.NoSuchElementException}.
-         * <p>
-         * This method reuses findMax method and passes entities along with prepare comparator instance,
-         * that is stored as constant CREATED_ON_COMPARATOR.
-         *
-         * @param entities provided collection of entities
-         * @param <T>      entity type
-         * @return an entity from the given collection that has the max createdOn value
-         */
-        // todo: create a method according to JavaDoc and implement it using previous method
-
-        /**
-         * An util method that allows to swap two elements of any list. It changes the list so the element with the index
-         * i will be located on index j, and the element with index j, will be located on the index i.
-         * Please note that in order to make it convenient and simple, it DOES NOT declare any type parameter.
-         *
-         * @param elements a list of any given type
-         * @param i        index of the element to swap
-         * @param j        index of the other element to swap
-         */
         public static void swap(List<?> elements, int i, int j) {
             Objects.checkIndex(i, elements.size());
             Objects.checkIndex(j, elements.size());
-            throw new ExerciseNotCompletedException(); // todo: complete method implementation 
+            swapHelper(elements, i, j);
+        }
+
+
+        private static <T> void swapHelper(List<T> list, int i, int j) {
+            T tmp = list.get(i);
+            list.set(i, list.get(j));
+            list.set(j, tmp);
         }
 
     }
 }
+
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