Java expert path

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

@@ -1,6 +1,7 @@
 package com.bobocode.intro;
 
-import com.bobocode.util.ExerciseNotCompletedException;
+import java.nio.charset.StandardCharsets;
+import java.util.Base64;
 
 /**
  * Welcome! This is an introduction exercise that will show you a simple example of Bobocode exercises.
@@ -23,8 +24,7 @@ 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 +39,6 @@ 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(StandardCharsets.UTF_8));
     }
 }

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 +9,13 @@
  */
 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());
+        var intBox = new Box<>(123);
+        var intBox2 = new Box<>(321);
+        System.out.println(intBox.getValue() + intBox2.getValue());
 
         intBox.setValue(222);
-        intBox.setValue("abc"); // this should not be allowed
+//        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());
+        System.out.println(intBox.getValue() + intBox2.getValue());
     }
 }

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

@@ -5,10 +5,10 @@
 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;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
 
 /**
  * {@link CrazyGenerics} is an exercise class. It consists of classes, interfaces and methods that should be updated
@@ -33,8 +33,8 @@ 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 +45,11 @@ 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 +59,8 @@ 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>{ // todo: introduce type parameters
+        R convert(T value);
     }
 
     /**
@@ -70,10 +70,10 @@ 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 +82,11 @@ 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) {
+            this.max = max.compareTo(val) < 0 ? val : max;
         }
 
-        public Object getMax() {
+        public T getMax() {
             return max;
         }
     }
@@ -97,8 +97,8 @@ 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 Comparable<? super T> & Serializable> { // todo: make it generic
+        void process(T obj);
     }
 
     /**
@@ -108,10 +108,10 @@ 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 +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
     }
 
     /**
@@ -133,7 +133,11 @@ 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());
+        }
     }
 
     /**
@@ -147,7 +151,7 @@ static class CollectionUtil {
          *
          * @param list
          */
-        public static void print(List<Integer> list) {
+        public static void print(List<?> 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 +164,8 @@ 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(entity -> entity.getUuid() == null);
         }
 
         /**
@@ -173,8 +177,8 @@ 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 +191,8 @@ 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(entity -> entity.getUuid().equals(targetEntity.getUuid())).count() > 1;
         }
 
         /**
@@ -201,7 +205,18 @@ 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<T> comparator) {
+            T max = null;
+            Iterator<T> iterator = elements.iterator();
+            while (iterator.hasNext()) {
+                var element = iterator.next();
+                if (max == null) { max = element; }
+                if (comparator.compare(element, max) > 0) {
+                    max = element;
+                };
+            }
+           return Optional.ofNullable(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,
@@ -215,7 +230,10 @@ 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){
+            if (entities == null || entities.isEmpty()) throw new NoSuchElementException();
+            return (T) findMax(entities.stream().collect(Collectors.toUnmodifiableSet()), CREATED_ON_COMPARATOR).get();
+        }
         /**
          * 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.
@@ -228,7 +246,11 @@ 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 
+            var elementI = elements.get(i);
+            var elementJ = elements.get(j);
+            final List l = elements;
+            l.set(i, elementJ);
+            l.set(j, elementI);
         }
 
     }

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

@@ -1,5 +1,7 @@
 package com.bobocode.basics;
 
+import java.util.Comparator;
+import java.util.HashMap;
 import java.util.Map;
 
 /**
@@ -16,6 +18,8 @@
  */
 public class HeterogeneousMaxHolder {
 
+    private final Map<Class<?>, Object> map = 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
      * of this method makes sure that only max value is stored and everything else is ignored.
@@ -31,7 +35,17 @@ public class HeterogeneousMaxHolder {
      * @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) {
+        if (!map.containsKey(key)) {
+            map.put(key, value);
+            return null;
+        }
+        var storedValue = (T) map.get(key);
+        if (value.compareTo(storedValue) > 0) {
+            map.put(key, value);
+            return storedValue;
+        } else return value;
+    }
     /**
      * An overloaded method put implements the same logic using a custom comparator. A given comparator is wrapped with
      * a null-safe comparator, considering null smaller than any non-null object.
@@ -45,7 +59,17 @@ public class HeterogeneousMaxHolder {
      * @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) {
+        if (!map.containsKey(key)) {
+            map.put(key, value);
+            return null;
+        }
+        var storedValue = (T) map.get(key);
+        if (comparator.compare(value, storedValue) > 0) {
+            map.put(key, value);
+            return storedValue;
+        } else 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.
      *
@@ -54,4 +78,7 @@ public class HeterogeneousMaxHolder {
      * @return current max value or null
      */
     // todo: implement a method according to javadoc
+    public <T> T getMax(Class<T> key) {
+        return (T) map.get(key);
+    }
 }

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;
+
+@Retention(RetentionPolicy.RUNTIME)
+@Target(ElementType.TYPE)
+public @interface Exercise {
+    String name() default "hello-annotation-basic";
+    String value() default "";
+    Level complexityLevel() default Level.BASIC;
+}

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

@@ -13,5 +13,7 @@
  *
  * @author Taras Boychuk
  */
-public class HelloAnnotationsExercise { // todo: mark class with the annotation according to the javadoc
+@Exercise(value = "hello-annotation-basic", complexityLevel = Level.BASIC)
+public class HelloAnnotationsExercise {
+
 }