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‎algorithms-miscellaneous-6/README.md‎

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- [Efficiently Merge Sorted Java Sequences](https://www.baeldung.com/java-merge-sorted-sequences)
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- [Introduction to Greedy Algorithms with Java](https://www.baeldung.com/java-greedy-algorithms)
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- [The Caesar Cipher in Java](https://www.baeldung.com/java-caesar-cipher)
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- [Implementing a 2048 Solver in Java](https://www.baeldung.com/2048-java-solver)
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- [Finding Top K Elements in an Array](https://www.baeldung.com/java-array-top-elements)
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- More articles: [[<-- prev]](/../algorithms-miscellaneous-5)

‎algorithms-miscellaneous-6/src/main/java/com/baeldung/algorithms/topkelements/BruteForceTopKElementsFinder.java‎

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package com.baeldung.algorithms.topkelements;
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import java.util.ArrayList;
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import java.util.List;
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public class BruteForceTopKElementsFinder implements TopKElementsFinder<Integer> {
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public List<Integer> findTopK(List<Integer> input, int k) {
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List<Integer> array = new ArrayList<>(input);
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List<Integer> topKList = new ArrayList<>();
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for (int i = 0; i < k; i++) {
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int maxIndex = 0;
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for (int j = 1; j < array.size(); j++) {
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if (array.get(j) > array.get(maxIndex)) {
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maxIndex = j;
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}
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}
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topKList.add(array.remove(maxIndex));
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}
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return topKList;
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}
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}

‎algorithms-miscellaneous-6/src/main/java/com/baeldung/algorithms/topkelements/MaxHeapTopKElementsFinder.java‎

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package com.baeldung.algorithms.topkelements;
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import java.util.ArrayList;
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import java.util.Collections;
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import java.util.List;
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import java.util.PriorityQueue;
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public class MaxHeapTopKElementsFinder implements TopKElementsFinder<Integer> {
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public List<Integer> findTopK(List<Integer> input, int k) {
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PriorityQueue<Integer> maxHeap = new PriorityQueue<>();
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input.forEach(number -> {
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maxHeap.add(number);
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if (maxHeap.size() > k) {
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maxHeap.poll();
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}
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});
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List<Integer> topKList = new ArrayList<>(maxHeap);
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Collections.reverse(topKList);
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return topKList;
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}
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}

‎algorithms-miscellaneous-6/src/main/java/com/baeldung/algorithms/topkelements/TopKElementsFinder.java‎

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package com.baeldung.algorithms.topkelements;
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import java.util.List;
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public interface TopKElementsFinder<T extends Comparable<T>> {
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List<T> findTopK(List<T> input, int k);
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}

‎algorithms-miscellaneous-6/src/main/java/com/baeldung/algorithms/topkelements/TreeSetTopKElementsFinder.java‎

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package com.baeldung.algorithms.topkelements;
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import java.util.Comparator;
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import java.util.List;
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import java.util.Set;
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import java.util.TreeSet;
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import java.util.stream.Collectors;
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public class TreeSetTopKElementsFinder implements TopKElementsFinder<Integer> {
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public List<Integer> findTopK(List<Integer> input, int k) {
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Set<Integer> sortedSet = new TreeSet<>(Comparator.reverseOrder());
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sortedSet.addAll(input);
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return sortedSet.stream().limit(k).collect(Collectors.toList());
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}
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}

‎algorithms-miscellaneous-6/src/test/java/com/baeldung/algorithms/topkelements/TopKElementsFinderUnitTest.java‎

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package com.baeldung.algorithms.topkelements;
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import org.junit.Test;
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import java.util.Arrays;
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import java.util.List;
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import static org.assertj.core.api.Java6Assertions.assertThat;
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public class TopKElementsFinderUnitTest {
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private final TopKElementsFinder<Integer> bruteForceFinder = new BruteForceTopKElementsFinder();
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private final TopKElementsFinder<Integer> maxHeapFinder = new MaxHeapTopKElementsFinder();
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private final TopKElementsFinder<Integer> treeSetFinder = new TreeSetTopKElementsFinder();
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private final int k = 4;
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private final List<Integer> distinctIntegers = Arrays.asList(1, 2, 3, 9, 7, 6, 12);
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private final List<Integer> distinctIntegersTopK = Arrays.asList(9, 7, 6, 12);
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private final List<Integer> nonDistinctIntegers = Arrays.asList(1, 2, 3, 3, 9, 9, 7, 6, 12);
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private final List<Integer> nonDistinctIntegersTopK = Arrays.asList(9, 9, 7, 12);
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@Test
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public void givenArrayDistinctIntegers_whenBruteForceFindTopK_thenReturnKLargest() {
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assertThat(bruteForceFinder.findTopK(distinctIntegers, k)).containsOnlyElementsOf(distinctIntegersTopK);
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}
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@Test
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public void givenArrayDistinctIntegers_whenMaxHeapFindTopK_thenReturnKLargest() {
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assertThat(maxHeapFinder.findTopK(distinctIntegers, k)).containsOnlyElementsOf(distinctIntegersTopK);
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}
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@Test
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public void givenArrayDistinctIntegers_whenTreeSetFindTopK_thenReturnKLargest() {
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assertThat(treeSetFinder.findTopK(distinctIntegers, k)).containsOnlyElementsOf(distinctIntegersTopK);
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}
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@Test
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public void givenArrayNonDistinctIntegers_whenBruteForceFindTopK_thenReturnKLargest() {
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assertThat(bruteForceFinder.findTopK(nonDistinctIntegers, k)).containsOnlyElementsOf(nonDistinctIntegersTopK);
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}
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@Test
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public void givenArrayNonDistinctIntegers_whenMaxHeapFindTopK_thenReturnKLargest() {
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assertThat(maxHeapFinder.findTopK(nonDistinctIntegers, k)).containsOnlyElementsOf(nonDistinctIntegersTopK);
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}
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}

‎apache-shiro/README.md‎

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- [Introduction to Apache Shiro](https://www.baeldung.com/apache-shiro)
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- [Permissions-Based Access Control with Apache Shiro](https://www.baeldung.com/apache-shiro-access-control)
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- [Spring Security vs Apache Shiro](https://www.baeldung.com/spring-security-vs-apache-shiro)

‎core-groovy/README.md‎

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- [Converting a String to a Date in Groovy](https://www.baeldung.com/groovy-string-to-date)
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- [Guide to I/O in Groovy](https://www.baeldung.com/groovy-io)
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- [Convert String to Integer in Groovy](https://www.baeldung.com/groovy-convert-string-to-integer)
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- [Groovy Variable Scope](https://www.baeldung.com/groovy/variable-scope)
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- [[More -->]](/core-groovy-2)

‎core-java-modules/core-java-11/README.md‎

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- [Java 11 Local Variable Syntax for Lambda Parameters](https://www.baeldung.com/java-var-lambda-params)
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- [Java 11 String API Additions](https://www.baeldung.com/java-11-string-api)
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- [Java 11 Nest Based Access Control](https://www.baeldung.com/java-nest-based-access-control)
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- [Exploring the New HTTP Client in Java 9 and 11](https://www.baeldung.com/java-9-http-client)
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- [Exploring the New HTTP Client in Java](https://www.baeldung.com/java-9-http-client)
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- [An Introduction to Epsilon GC: A No-Op Experimental Garbage Collector](https://www.baeldung.com/jvm-epsilon-gc-garbage-collector)
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- [Guide to jlink](https://www.baeldung.com/jlink)
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- [Negate a Predicate Method Reference with Java 11](https://www.baeldung.com/java-negate-predicate-method-reference)

‎core-java-modules/core-java-9-jigsaw/src/simple-modules/main.app/com/baeldung/modules/main/MainApp.java‎

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package com.baeldung.modules.main;
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import com.baeldung.modules.hello.HelloInterface;
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import com.baeldung.modules.hello.HelloModules;
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import java.util.ServiceLoader;
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public class MainApp {
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public static void main(String[] args) {
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HelloModules.doSomething();
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HelloModules module = new HelloModules();
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module.sayHello();
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Iterable<HelloInterface> services = ServiceLoader.load(HelloInterface.class);
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HelloInterface service = services.iterator().next();
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service.sayHello();
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}
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}

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