Completed Solution & Discussion #33

Original file line number	Diff line number	Diff line change
		@@ -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.
Expand All		@@ -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!";
		}

		/**
Expand All		@@ -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());
		}
		}

10 changes: 5 additions & 5 deletions 1-0-java-basics/1-3-0-hello-generics/src/main/java/com/bobocode/basics/Box.java

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Original file line number	Diff line number	Diff line change
Expand Up		@@ -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;
		}
		}

11 changes: 5 additions & 6 deletions 1-0-java-basics/1-3-0-hello-generics/src/main/java/com/bobocode/basics/BoxDemoApp.java

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Original file line number	Diff line number	Diff line change
Expand Up		@@ -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());
		}
		}

108 changes: 67 additions & 41 deletions 1-0-java-basics/1-3-1-crazy-generics/src/main/java/com/bobocode/basics/CrazyGenerics.java

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Original file line number	Diff line number	Diff line change
		@@ -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
Expand All		@@ -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;
		}

Expand All		@@ -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;
		}

		/**
Expand All		@@ -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);
		}

		/**
Expand All		@@ -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;
		}

Expand All		@@ -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;
		}
		}
Expand All		@@ -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);
		}

		/**
Expand All		@@ -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();
		}

		/**
Expand All		@@ -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
		}

		/**
Expand All		@@ -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);

Expand All		@@ -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));
		}

Expand All		@@ -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);
		}

		/**
Expand All		@@ -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);
		}

		/**
Expand All		@@ -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;
		}

		/**
Expand All		@@ -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
Expand All		@@ -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
Expand All		@@ -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);
	}
		}
		}

30 changes: 25 additions & 5 deletions ...-2-heterogeneous-max-holder/src/main/java/com/bobocode/basics/HeterogeneousMaxHolder.java

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Original file line number	Diff line number	Diff line change
		@@ -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.
Expand All		@@ -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
Expand All		@@ -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
Expand All		@@ -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);
	}
		}

14 changes: 14 additions & 0 deletions 1-0-java-basics/1-5-0-hello-annotations/src/main/java/com/bobocode/basics/Exercise.java

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Original file line number	Diff line number	Diff line change
		@@ -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 change: 1 addition & 0 deletions ...s/1-5-0-hello-annotations/src/main/java/com/bobocode/basics/HelloAnnotationsExercise.java

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

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