0-0 done

.vscode/settings.json

@@ -0,0 +1,3 @@
+{
+    "java.compile.nullAnalysis.mode": "disabled"
+}

0-0-intro/src/main/java/com/bobocode/intro/ExerciseIntroduction.java

@@ -1,5 +1,7 @@
 package com.bobocode.intro;
 
+import java.util.Base64;
+
 import com.bobocode.util.ExerciseNotCompletedException;
 
 /**
@@ -24,7 +26,7 @@ public class ExerciseIntroduction {
      */
     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!"; 
     }
 
     /**
@@ -39,7 +41,6 @@ public String getWelcomeMessage() {
      * @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());
     }
 }

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;
     }
 }

1-0-java-basics/1-3-1-crazy-generics/src/main/java/com/bobocode/basics/CrazyGenerics.java

@@ -5,10 +5,7 @@
 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.*;
 
 /**
  * {@link CrazyGenerics} is an exercise class. It consists of classes, interfaces and methods that should be updated
@@ -33,8 +30,8 @@ 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 +42,11 @@ public static class Sourced { // todo: refactor class to introduce type paramete
      * @param <T> – actual, min and max type
      */
     @Data
-    public static class Limited {
+    public static class Limited <T extends Number> {
         // 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;
+        private final T actual;
+        private final T min;
+        private final T max;
     }
 
     /**
@@ -59,8 +56,9 @@ public static class Limited {
      * @param <T> – source object type
      * @param <R> - converted result type
      */
-    public interface Converter { // todo: introduce type parameters
+    public interface Converter <T, R> { // todo: introduce type parameters
         // todo: add convert method
+        R convert(T value);
     }
 
     /**
@@ -70,10 +68,10 @@ 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<T>> { // todo: refactor class to make it generic
+        private T max;
 
-        public MaxHolder(Object max) {
+        public MaxHolder(T max) {
             this.max = max;
         }
 
@@ -82,11 +80,14 @@ 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) { // todo: update parameter and implement the method
+            if (val.compareTo(max) > 0) {
+                max = val;
+            }
         }
 
-        public Object getMax() {
+        public T getMax() {
             return max;
         }
     }
@@ -97,8 +98,8 @@ 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<T>> { // todo: make it generic
+        void process(T obj);
     }
 
     /**
@@ -108,10 +109,9 @@ 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);
-
-        Collection<Object> getEntityCollection();
+    interface CollectionRepository <T extends BaseEntity, C extends Collection<T>> { // todo: update interface according to the javadoc
+        void save(T entity);
+        C getEntityCollection();
     }
 
     /**
@@ -120,7 +120,7 @@ interface CollectionRepository { // todo: update interface according to the java
      *
      * @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>> { // todo: update interface according to the javadoc
     }
 
     /**
@@ -133,8 +133,8 @@ 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<?>> { // todo: refactor it to make generic and provide a default impl of compareTo
+    } //інтерфейс типу Е являє собою колекцію типу Е, і при цьому може порівнюватися з колекціями, де елементи будь яких типів
 
     /**
      * {@link CollectionUtil} is an util class that provides various generic helper methods.
@@ -147,7 +147,7 @@ static class CollectionUtil {
          *
          * @param list
          */
-        public static void print(List<Integer> list) {
+        public static <T> void print(List<T> list) {
             // todo: refactor it so the list of any type can be printed, not only integers
             list.forEach(element -> System.out.println(" – " + element));
         }
@@ -160,8 +160,16 @@ 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 <E extends BaseEntity> boolean hasNewEntities(Collection<E> entities) {
+            if (entities == null || entities.isEmpty()) { // todo: refactor parameter and implement method
+                return false;
+            }
+            for (E entity : entities) {
+                if (null == entity.getUuid()) {
+                    return true;
+                }
+            }
+            return false;
         }
 
         /**
@@ -173,8 +181,12 @@ 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 <E extends BaseEntity> boolean isValidCollection(Collection<E> entities, java.util.function.Predicate<E> validationPredicate) {
+            if (entities == null || entities.isEmpty()) return false;  // todo: add method parameters and implement the logic
+            for (E entity : entities) {
+                if (!validationPredicate.test(entity)) return false;
+            }
+            return true;
         }
 
         /**
@@ -187,8 +199,13 @@ 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(List<T> entities, T targetEntity) {
+            for (T entity : entities) {// todo: update method signature and implement it
+                if (entity.getUuid() == (targetEntity.getUuid())) {
+                    return true;
+                }
+            }
+            return false;
         }
 
         /**
@@ -201,6 +218,20 @@ public static boolean hasDuplicates() {
          * @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) {
+                var iterator = elements.iterator();
+                if (!iterator.hasNext()) {
+                    return Optional.empty();
+                }
+                var max = iterator.next();
+                while (iterator.hasNext()) {
+                    var element = iterator.next();
+                    if (comparator.compare(element, max) > 0) {
+                        max = element;
+                    }
+                }
+                return Optional.of(max);
+            }
 
         /**
          * findMostRecentlyCreatedEntity is a generic util method that accepts a collection of entities and returns the
@@ -215,6 +246,10 @@ public static boolean hasDuplicates() {
          * @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
@@ -225,11 +260,18 @@ public static boolean hasDuplicates() {
          * @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 
-        }
+            public static void swap(List<?> elements, int i, int j) {
+                Objects.checkIndex(i, elements.size());
+                Objects.checkIndex(j, elements.size());
+                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);
+            }
 
     }
 }
+

1-0-java-basics/1-3-1-crazy-generics/src/main/java/com/bobocode/basics/util/BaseEntity.java

@@ -18,4 +18,5 @@ public BaseEntity(UUID uuid) {
         this.uuid = uuid;
         this.createdOn = LocalDateTime.now();
     }
+
 }