Completed Solution & Discussion

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.
@@ -23,8 +23,7 @@ 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!"; 
     }
 
     /**
@@ -39,7 +38,6 @@ 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/1-3-0-hello-generics/src/main/java/com/bobocode/basics/BoxDemoApp.java

@@ -9,13 +9,12 @@
  */
 public class BoxDemoApp {
     public static void main(String[] args) {
-        Box intBox = new Box(123);
-        Box intBox2 = new Box(321);
-        System.out.println((int) intBox.getValue() + (int) intBox2.getValue());
+        Box<Integer> intBox = new Box<>(123);
+        Box<Integer> intBox2 = new Box<>(321);
+        System.out.println((int) intBox.getValue() + intBox2.getValue());
 
         intBox.setValue(222);
-        intBox.setValue("abc"); // this should not be allowed
-        // the following code will compile, but will throw runtime exception
-        System.out.println((int) intBox.getValue() + (int) intBox2.getValue());
+//        intBox.setValue("abc"); // this should not be allowed
+        System.out.println((int) intBox.getValue() + intBox2.getValue());
     }
 }

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

@@ -1,14 +1,12 @@
 package com.bobocode.basics;
 
 import com.bobocode.basics.util.BaseEntity;
-import com.bobocode.util.ExerciseNotCompletedException;
 import lombok.Data;
+import lombok.val;
 
 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> {
+        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 obj);
     }
 
     /**
@@ -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>> { // todo: refactor class to make it generic
+        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>> { // todo: make it generic
+        void process(T obj);
     }
 
     /**
@@ -108,10 +107,10 @@ 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>> { // todo: update interface according to the javadoc
+        void save(T entity);
 
-        Collection<Object> getEntityCollection();
+        C getEntityCollection();
     }
 
     /**
@@ -120,7 +119,7 @@ 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
     }
 
     /**
@@ -133,12 +132,14 @@ 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<?> 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);
 
@@ -147,8 +148,7 @@ 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 +160,9 @@ 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);
         }
 
         /**
@@ -173,8 +174,10 @@ 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);
         }
 
         /**
@@ -187,8 +190,10 @@ 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;
         }
 
         /**
@@ -200,7 +205,20 @@ 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) {
+            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
@@ -214,7 +232,10 @@ 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
@@ -228,8 +249,13 @@ 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);
+        }
     }
 }

1-0-java-basics/1-3-2-heterogeneous-max-holder/src/main/java/com/bobocode/basics/HeterogeneousMaxHolder.java

@@ -1,7 +1,11 @@
 package com.bobocode.basics;
 
+import java.util.Comparator;
+import java.util.HashMap;
 import java.util.Map;
 
+import static java.util.Objects.requireNonNull;
+
 /**
  * {@link HeterogeneousMaxHolder} is a multi-type container that holds maximum values per each type. It's kind of a
  * key/value map, where the key is a type and the value is the maximum among all values of this type that were put.
@@ -15,9 +19,10 @@
  * @author Taras Boychuk
  */
 public class HeterogeneousMaxHolder {
+    private Map<Class<?>, Object> typeToMaxValueMap = new HashMap<>();
 
     /**
-     * A method put stores a provided value by its type, if the value is greater than the current maximum. In other words, the logic
+     * Stores a provided value by its type, if the value is greater than the current maximum. In other words, the logic
      * of this method makes sure that only max value is stored and everything else is ignored.
      * <p>
      * If the current max value is less than a provided one, or if it's null, then a provided value gets stored and the old
@@ -30,7 +35,9 @@ public class HeterogeneousMaxHolder {
      * @param <T>   value type parameter
      * @return a smaller value among the provided value and the current maximum
      */
-    // todo: implement a method according to javadoc
+    public <T extends Comparable<? super T>> T put(Class<T> key, T value) {
+        return put(key, value, Comparator.naturalOrder());
+    }
 
     /**
      * An overloaded method put implements the same logic using a custom comparator. A given comparator is wrapped with
@@ -44,14 +51,27 @@ public class HeterogeneousMaxHolder {
      * @param <T>        value type parameter
      * @return a smaller value among the provided value and the current maximum
      */
-    // todo: implement a method according to javadoc
+    public <T> T put(Class<T> key, T value, Comparator<? super T> comparator) {
+        var currentMax = getMax(requireNonNull(key));
+        var nullSafeComparator = Comparator.nullsFirst(requireNonNull(comparator));
+        requireNonNull(value);
+        if (nullSafeComparator.compare(value, currentMax) > 0) {
+            typeToMaxValueMap.put(key, value);
+            return currentMax;
+        }
+        return value;
+    }
 
     /**
-     * A method getMax returns a max value by the given type. If no value is stored by this type, then it returns null.
+     * Returns a max value by the given type. If no value is stored by this type, then it returns null.
      *
      * @param key a provided value type
      * @param <T> value type parameter
      * @return current max value or null
      */
-    // todo: implement a method according to javadoc
+    public <T> T getMax(Class<T> key) {
+        requireNonNull(key);
+        var currentMax = typeToMaxValueMap.get(key);
+        return key.cast(currentMax);
+    }
 }

1-0-java-basics/1-5-0-hello-annotations/src/main/java/com/bobocode/basics/Exercise.java

@@ -0,0 +1,14 @@
+package com.bobocode.basics;
+
+import java.lang.annotation.ElementType;
+import java.lang.annotation.Retention;
+import java.lang.annotation.RetentionPolicy;
+import java.lang.annotation.Target;
+
+@Target(ElementType.TYPE)
+@Retention(RetentionPolicy.RUNTIME)
+public @interface Exercise {
+    String value();
+
+    Level complexityLevel() default Level.BASIC;
+}

1-0-java-basics/1-5-0-hello-annotations/src/main/java/com/bobocode/basics/HelloAnnotationsExercise.java

@@ -13,5 +13,6 @@
  *
  * @author Taras Boychuk
  */
+@Exercise("hello-annotation-basic")
 public class HelloAnnotationsExercise { // todo: mark class with the annotation according to the javadoc
 }