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..e0d0514d2 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
@@ -1,6 +1,6 @@
 package com.bobocode.intro;
 
-import com.bobocode.util.ExerciseNotCompletedException;
+import java.util.Base64;
 
 /**
 * Welcome! This is an introduction exercise that will show you a simple example of Bobocode exercises.
@@ -23,23 +23,13 @@ public class ExerciseIntroduction {
 * @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/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..0a1630d53 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
@@ -5,20 +5,19 @@
 * is flexible, because we can store anything we want there. But it is not safe, because it requires runtime casting
 * and there is no guarantee that we know the type of the stored value.
 * <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/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..1b320c076 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
@@ -5,10 +5,8 @@
 import lombok.Data;
 
 import java.io.Serializable;
-import java.util.Collection;
-import java.util.Comparator;
-import java.util.List;
-import java.util.Objects;
+import java.util.*;
+import java.util.function.Predicate;
 
 /**
 * {@link CrazyGenerics} is an exercise class. It consists of classes, interfaces and methods that should be updated
@@ -33,8 +31,8 @@ public class CrazyGenerics {
 * @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> { // todo: refactor class to introduce type parameter and make value generic
+ private T value;
 private String source;
 }
 
@@ -45,11 +43,10 @@ public static class Sourced { // todo: refactor class to introduce type paramete
 * @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;
 }
 
 /**
@@ -59,8 +56,8 @@ public static class Limited {
 * @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 value);
 }
 
 /**
@@ -70,10 +67,10 @@ public interface Converter { // todo: introduce type parameters
 *
 * @param <t> – value type
 */
- public static class MaxHolder { // todo: refactor class to make it generic
- private Object max;
+ public static class MaxHolder<t extends Comparable<? super T>> {
+ private T max;
 
- public MaxHolder(Object max) {
+ public MaxHolder(T max) {
 this.max = max;
 }
 
@@ -82,11 +79,13 @@ public MaxHolder(Object max) {
 *
 * @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.compareTo(max)> 0) {
+ max = val;
+ }
 }
 
- public Object getMax() {
+ public T getMax() {
 return max;
 }
 }
@@ -97,8 +96,8 @@ public Object getMax() {
 *
 * @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);
 }
 
 /**
@@ -108,19 +107,21 @@ interface StrictProcessor { // todo: make it generic
 * @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);
+ interface CollectionRepository<t extends BaseEntity, C extends Collection<t>> {
+ void save(T entity);
 
- Collection getEntityCollection();
+ 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>> {
+
 }
 
 /**
@@ -133,7 +134,12 @@ interface ListRepository { // todo: update interface according to the javadoc
 *
 * @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<?> e) {
+ return Integer.compare(this.size(), e.size());
+ }
 }
 
 /**
@@ -147,8 +153,8 @@ static class CollectionUtil {
 *
 * @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));
 }
 
@@ -160,8 +166,9 @@ public static void print(List<integer> list) {
 * @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) {
+ return entities.stream()
+ .anyMatch(e -> e.getUuid() == null);
 }
 
 /**
@@ -173,10 +180,13 @@ public static boolean hasNewEntities(Collection<baseentity> 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 boolean isValidCollection(Collection<? extends BaseEntity> entities,
+ Predicate<? super BaseEntity> validationPredicate) {
+ return entities.stream()
+ .allMatch(validationPredicate);
 }
 
+
 /**
 * 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
@@ -187,8 +197,10 @@ public static boolean isValidCollection() {
 * @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 extends BaseEntity> boolean hasDuplicates(Collection<t> entities, T targetEntity) {
+ return entities.stream()
+ .filter(e -> e.getUuid().equals(targetEntity.getUuid()))
+ .count()> 1;
 }
 
 /**
@@ -200,8 +212,21 @@ public static boolean hasDuplicates() {
 * @param <t> type of elements
 * @return optional max value
 */
- // todo: create a method and implement its logic manually without using util method from JDK
 
+ public static <t> Optional<t> findMax(Iterable<t> elements, Comparator<? super T> comparator) {
+ Iterator<t> iterator = elements.iterator();
+ T max = iterator.next();
+
+ while (iterator.hasNext()) {
+ T current = iterator.next();
+
+ if (comparator.compare(current, max)> 0) {
+ max = current;
+ }
+ }
+
+ return Optional.of(max);
+ }
 /**
 * 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,
@@ -214,7 +239,11 @@ public static boolean hasDuplicates() {
 * @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
+
+ public static <t extends BaseEntity> T findMostRecentlyCreatedEntity(Collection<t> entities) {
+ return findMax(entities, CREATED_ON_COMPARATOR)
+ .orElseThrow();
+ }
 
 /**
 * An util method that allows to swap two elements of any list. It changes the list so the element with the index
@@ -228,7 +257,13 @@ public static boolean hasDuplicates() {
 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> elements, int i, int j) {
+ T temp = elements.get(i);
+ elements.set(i, elements.get(j));
+ elements.set(j, temp);
 }
 
 }
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