Split or move core-java-collections module (#7842)

core-java-modules/core-java-collections-3/src/main/java/com/baeldung/collections/arraylistvsvector/ArrayListBenchmark.java

@@ -0,0 +1,90 @@
+package com.baeldung.collections.arraylistvsvector;
+
+import org.openjdk.jmh.annotations.*;
+import org.openjdk.jmh.runner.Runner;
+import org.openjdk.jmh.runner.options.Options;
+import org.openjdk.jmh.runner.options.OptionsBuilder;
+
+import java.util.*;
+import java.util.concurrent.TimeUnit;
+
+@BenchmarkMode(Mode.AverageTime)
+@OutputTimeUnit(TimeUnit.NANOSECONDS)
+@Warmup(iterations = 10)
+public class ArrayListBenchmark {
+
+    @State(Scope.Thread)
+    public static class MyState {
+
+        List<Employee> employeeList = new ArrayList<>();
+        Vector<Employee> employeeVector = new Vector<>();
+        //LinkedList<Employee> employeeList = new LinkedList<>();
+
+        long iterations = 100000;
+
+        Employee employee = new Employee(100L, "Harry");
+
+        int employeeIndex = -1;
+
+        @Setup(Level.Trial)
+        public void setUp() {
+            for (long i = 0; i < iterations; i++) {
+                employeeList.add(new Employee(i, "John"));
+                employeeVector.add(new Employee(i, "John"));
+            }
+
+            employeeList.add(employee);
+            employeeVector.add(employee);
+            employeeIndex = employeeList.indexOf(employee);
+        }
+    }
+
+    @Benchmark
+    public void testAddAt(ArrayListBenchmark.MyState state) {
+        state.employeeList.add((int) (state.iterations), new Employee(state.iterations, "John"));
+    }
+
+    @Benchmark
+    public boolean testContains(ArrayListBenchmark.MyState state) {
+        return state.employeeList.contains(state.employee);
+    }
+
+    @Benchmark
+    public boolean testContainsVector(ArrayListBenchmark.MyState state) {
+        return state.employeeVector.contains(state.employee);
+    }
+
+    @Benchmark
+    public int testIndexOf(ArrayListBenchmark.MyState state) {
+        return state.employeeList.indexOf(state.employee);
+    }
+
+    @Benchmark
+    public Employee testGet(ArrayListBenchmark.MyState state) {
+        return state.employeeList.get(state.employeeIndex);
+    }
+
+    @Benchmark
+    public Employee testVectorGet(ArrayListBenchmark.MyState state) {
+        return state.employeeVector.get(state.employeeIndex);
+    }
+
+    @Benchmark
+    public boolean testRemove(ArrayListBenchmark.MyState state) {
+        return state.employeeList.remove(state.employee);
+    }
+
+    @Benchmark
+    public void testAdd(ArrayListBenchmark.MyState state) {
+        state.employeeList.add(new Employee(state.iterations + 1, "John"));
+    }
+
+    public static void main(String[] args) throws Exception {
+        Options options = new OptionsBuilder()
+                .include(ArrayListBenchmark.class.getSimpleName()).threads(3)
+                .forks(1).shouldFailOnError(true)
+                .shouldDoGC(true)
+                .jvmArgs("-server").build();
+        new Runner(options).run();
+    }
+}

core-java-modules/core-java-collections-3/src/main/java/com/baeldung/collections/arraylistvsvector/Employee.java

@@ -0,0 +1,55 @@
+package com.baeldung.collections.arraylistvsvector;
+
+public class Employee {
+
+    private Long id;
+    private String name;
+
+    public Employee(Long id, String name) {
+        this.name = name;
+        this.id = id;
+    }
+
+    public Long getId() {
+        return id;
+    }
+
+    public void setId(Long id) {
+        this.id = id;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (o == null || getClass() != o.getClass()) return false;
+
+        Employee employee = (Employee) o;
+
+        if (!id.equals(employee.id)) return false;
+        return name.equals(employee.name);
+
+    }
+
+    @Override
+    public int hashCode() {
+        int result = id.hashCode();
+        result = 31 * result + name.hashCode();
+        return result;
+    }
+
+    @Override
+    public String toString() {
+        return "Employee{" +
+                "id=" + id +
+                ", name='" + name + '\'' +
+                '}';
+    }
+}

core-java-modules/core-java-collections-3/src/main/java/com/baeldung/collections/arraylistvsvector/VectorExample.java

@@ -0,0 +1,27 @@
+package com.baeldung.collections.arraylistvsvector;
+
+import java.util.Enumeration;
+import java.util.Iterator;
+import java.util.Vector;
+
+public class VectorExample {
+
+    public static void main(String[] args) {
+
+        Vector<String> vector = new Vector<>();
+        vector.add("baeldung");
+        vector.add("Vector");
+        vector.add("example");
+
+        Enumeration e = vector.elements();
+        while(e.hasMoreElements()){
+            System.out.println(e.nextElement());
+        }
+
+        Iterator<String> iterator = vector.iterator();
+        while (iterator.hasNext()) {
+            System.out.println(iterator.next());
+        }
+    }
+
+}

core-java-modules/core-java-collections-3/src/main/java/com/baeldung/collections/containsperformance/CollectionsBenchmark.java

@@ -0,0 +1,59 @@
+package com.baeldung.collections.containsperformance;
+
+import org.openjdk.jmh.annotations.*;
+import org.openjdk.jmh.runner.Runner;
+import org.openjdk.jmh.runner.options.Options;
+import org.openjdk.jmh.runner.options.OptionsBuilder;
+
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+import java.util.concurrent.TimeUnit;
+
+@BenchmarkMode(Mode.AverageTime)
+@OutputTimeUnit(TimeUnit.NANOSECONDS)
+@Warmup(iterations = 5)
+public class CollectionsBenchmark {
+
+    @State(Scope.Thread)
+    public static class MyState {
+        private Set<Employee> employeeSet = new HashSet<>();
+        private List<Employee> employeeList = new ArrayList<>();
+
+        private long iterations = 10000;
+
+        private Employee employee = new Employee(100L, "Harry");
+
+        @Setup(Level.Trial)
+        public void setUp() {
+
+            for (long i = 0; i < iterations; i++) {
+                employeeSet.add(new Employee(i, "John"));
+                employeeList.add(new Employee(i, "John"));
+            }
+
+            employeeList.add(employee);
+            employeeSet.add(employee);
+        }
+    }
+
+    @Benchmark
+    public boolean testArrayList(MyState state) {
+        return state.employeeList.contains(state.employee);
+    }
+
+    @Benchmark
+    public boolean testHashSet(MyState state) {
+        return state.employeeSet.contains(state.employee);
+    }
+
+    public static void main(String[] args) throws Exception {
+        Options options = new OptionsBuilder()
+                .include(CollectionsBenchmark.class.getSimpleName()).threads(1)
+                .forks(1).shouldFailOnError(true)
+                .shouldDoGC(true)
+                .jvmArgs("-server").build();
+        new Runner(options).run();
+    }
+}

core-java-modules/core-java-collections-3/src/main/java/com/baeldung/collections/containsperformance/Employee.java

@@ -0,0 +1,55 @@
+package com.baeldung.collections.containsperformance;
+
+public class Employee {
+
+    private Long id;
+    private String name;
+
+    public Employee(Long id, String name) {
+        this.name = name;
+        this.id = id;
+    }
+
+    public Long getId() {
+        return id;
+    }
+
+    public void setId(Long id) {
+        this.id = id;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) return true;
+        if (o == null || getClass() != o.getClass()) return false;
+
+        Employee employee = (Employee) o;
+
+        if (!id.equals(employee.id)) return false;
+        return name.equals(employee.name);
+
+    }
+
+    @Override
+    public int hashCode() {
+        int result = id.hashCode();
+        result = 31 * result + name.hashCode();
+        return result;
+    }
+
+    @Override
+    public String toString() {
+        return "Employee{" +
+                "id=" + id +
+                ", name='" + name + '\'' +
+                '}';
+    }
+}

core-java-modules/core-java-collections-3/src/main/java/com/baeldung/collections/iterators/Iterators.java

@@ -0,0 +1,80 @@
+package com.baeldung.collections.iterators;
+
+import java.util.ArrayList;
+import java.util.Iterator;
+import java.util.concurrent.ConcurrentHashMap;
+
+/**
+ * Source code https://github.com/eugenp/tutorials
+ *
+ * @author Santosh Thakur
+ */
+
+public class Iterators {
+
+    public static int failFast1() {
+        ArrayList<Integer> numbers = new ArrayList<>();
+
+        numbers.add(10);
+        numbers.add(20);
+        numbers.add(30);
+        numbers.add(40);
+
+        Iterator<Integer> iterator = numbers.iterator();
+        while (iterator.hasNext()) {
+            Integer number = iterator.next();
+            numbers.add(50);
+        }
+
+        return numbers.size();
+    }
+
+    public static int failFast2() {
+        ArrayList<Integer> numbers = new ArrayList<>();
+        numbers.add(10);
+        numbers.add(20);
+        numbers.add(30);
+        numbers.add(40);
+
+        Iterator<Integer> iterator = numbers.iterator();
+        while (iterator.hasNext()) {
+            if (iterator.next() == 30) {
+                // will not throw Exception
+                iterator.remove();
+            }
+        }
+
+        System.out.println("using iterator's remove method = " + numbers);
+
+        iterator = numbers.iterator();
+        while (iterator.hasNext()) {
+            if (iterator.next() == 40) {
+                // will throw Exception on
+                // next call of next() method
+                numbers.remove(2);
+            }
+        }
+
+        return numbers.size();
+    }
+
+    public static int failSafe1() {
+        ConcurrentHashMap<String, Integer> map = new ConcurrentHashMap<>();
+
+        map.put("First", 10);
+        map.put("Second", 20);
+        map.put("Third", 30);
+        map.put("Fourth", 40);
+
+        Iterator<String> iterator = map.keySet()
+            .iterator();
+
+        while (iterator.hasNext()) {
+            String key = iterator.next();
+            map.put("Fifth", 50);
+        }
+
+        return map.size();
+    }
+
+}

core-java-modules/core-java-collections-3/src/main/java/com/baeldung/collections/sortingcomparison/ArraySortBenchmark.java

@@ -0,0 +1,51 @@
+package com.baeldung.collections.sortingcomparison;
+
+import java.util.Arrays;
+import java.util.concurrent.TimeUnit;
+
+import org.openjdk.jmh.annotations.Benchmark;
+import org.openjdk.jmh.annotations.BenchmarkMode;
+import org.openjdk.jmh.annotations.Measurement;
+import org.openjdk.jmh.annotations.Mode;
+import org.openjdk.jmh.annotations.OutputTimeUnit;
+import org.openjdk.jmh.annotations.Scope;
+import org.openjdk.jmh.annotations.State;
+import org.openjdk.jmh.annotations.Warmup;
+import org.openjdk.jmh.runner.Runner;
+import org.openjdk.jmh.runner.options.Options;
+import org.openjdk.jmh.runner.options.OptionsBuilder;
+
+@BenchmarkMode(Mode.AverageTime)
+@OutputTimeUnit(TimeUnit.MILLISECONDS)
+@Measurement(batchSize = 100000, iterations = 10)
+@Warmup(batchSize = 100000, iterations = 10)
+public class ArraySortBenchmark {
+
+    @State(Scope.Thread)
+    public static class Initialize {
+        Integer[] numbers = { -769214442, -1283881723, 1504158300, -1260321086, -1800976432, 1278262737, 1863224321, 1895424914, 2062768552, -1051922993, 751605209, -1500919212, 2094856518, -1014488489, -931226326, -1677121986, -2080561705, 562424208, -1233745158, 41308167 };
+        int[] primitives = { -769214442, -1283881723, 1504158300, -1260321086, -1800976432, 1278262737, 1863224321, 1895424914, 2062768552, -1051922993, 751605209, -1500919212, 2094856518, -1014488489, -931226326, -1677121986, -2080561705, 562424208, -1233745158, 41308167 };
+    }
+
+    @Benchmark
+    public Integer[] benchmarkArraysIntegerSort(ArraySortBenchmark.Initialize state) {
+        Arrays.sort(state.numbers);
+        return state.numbers;
+    }
+
+    @Benchmark
+    public int[] benchmarkArraysIntSort(ArraySortBenchmark.Initialize state) {
+        Arrays.sort(state.primitives);
+        return state.primitives;
+    }
+
+
+    public static void main(String[] args) throws Exception {
+        Options options = new OptionsBuilder()
+                .include(ArraySortBenchmark.class.getSimpleName()).threads(1)
+                .forks(1).shouldFailOnError(true)
+                .shouldDoGC(true)
+                .jvmArgs("-server").build();
+        new Runner(options).run();
+    }
+}

core-java-modules/core-java-collections-3/src/main/java/com/baeldung/collections/sortingcomparison/CollectionsSortCompare.java

@@ -0,0 +1,39 @@
+package com.baeldung.collections.sortingcomparison;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+
+public class CollectionsSortCompare {
+
+    public static void main(String[] args) {
+        sortPrimitives();
+        sortReferenceType();
+        sortCollection();
+    }
+
+    private static void sortReferenceType() {
+        Integer[] numbers = {5, 22, 10, 0};
+        Arrays.sort(numbers);
+        System.out.println(Arrays.toString(numbers));
+    }
+
+    private static void sortCollection() {
+        List<Integer> numbersList = new ArrayList<>();
+        numbersList.add(5);
+        numbersList.add(22);
+        numbersList.add(10);
+        numbersList.add(0);
+
+        Collections.sort(numbersList);
+
+        numbersList.forEach(System.out::print);
+    }
+
+    private static void sortPrimitives() {
+        int[] numbers = {5, 22, 10, 0};
+        Arrays.sort(numbers);
+        System.out.println(Arrays.toString(numbers));
+    }
+}

core-java-modules/core-java-collections-3/src/test/java/com/baeldung/collections/clearvsremoveall/ClearVsRemoveAllUnitTest.java

@@ -0,0 +1,40 @@
+package com.baeldung.collections.clearvsremoveall;
+
+import org.junit.jupiter.api.Test;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collection;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertTrue;
+
+/**
+ * Unit tests demonstrating differences between ArrayList#clear() and ArrayList#removeAll()
+ */
+class ClearVsRemoveAllUnitTest {
+
+    /*
+     * Tests
+     */
+    @Test
+    void givenArrayListWithElements_whenClear_thenListBecomesEmpty() {
+        Collection<Integer> collection = new ArrayList<>(Arrays.asList(1, 2, 3, 4, 5));
+
+        collection.clear();
+
+        assertTrue(collection.isEmpty());
+    }
+
+    @Test
+    void givenTwoArrayListsWithCommonElements_whenRemoveAll_thenFirstListMissElementsFromSecondList() {
+        Collection<Integer> firstCollection = new ArrayList<>(Arrays.asList(1, 2, 3, 4, 5));
+        Collection<Integer> secondCollection = new ArrayList<>(Arrays.asList(3, 4, 5, 6, 7));
+
+        firstCollection.removeAll(secondCollection);
+
+        assertEquals(Arrays.asList(1, 2), firstCollection);
+        assertEquals(Arrays.asList(3, 4, 5, 6, 7), secondCollection);
+    }
+
+}

core-java-modules/core-java-collections-3/src/test/java/com/baeldung/collections/hashmapvshashtable/HashmapVsHashtableDifferenceUnitTest.java

@@ -0,0 +1,98 @@
+package com.baeldung.collections.hashmapvshashtable;
+
+import static org.junit.Assert.assertEquals;
+
+import java.util.Collections;
+import java.util.ConcurrentModificationException;
+import java.util.Enumeration;
+import java.util.HashMap;
+import java.util.Hashtable;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Map;
+import java.util.Map.Entry;
+import java.util.Set;
+
+import org.junit.Test;
+
+import com.google.common.collect.Lists;
+
+public class HashmapVsHashtableDifferenceUnitTest {
+
+    // null values
+    @Test(expected = NullPointerException.class)
+    public void givenHashtable_whenAddNullKey_thenNullPointerExceptionThrown() {
+        Hashtable<String, String> table = new Hashtable<String, String>();        
+        table.put(null, "value");
+    }
+    
+    @Test(expected = NullPointerException.class)
+    public void givenHashtable_whenAddNullValue_thenNullPointerExceptionThrown() {
+        Hashtable<String, String> table = new Hashtable<String, String>();        
+        table.put("key", null);
+    }
+    
+    @Test
+    public void givenHashmap_whenAddNullKeyAndValue_thenObjectAdded() {
+        HashMap<String, String> map = new HashMap<String, String>();
+        map.put(null, "value");
+        map.put("key1", null);
+        map.put("key2", null);
+        
+        assertEquals(3, map.size());
+    }
+    
+    // fail-fast iterator
+    @Test(expected = ConcurrentModificationException.class)
+    public void givenHashmap_whenModifyUnderlyingCollection_thenConcurrentModificationExceptionThrown() {
+        HashMap<String, String> map = new HashMap<String, String>();
+        map.put("key1", "value1");
+        map.put("key2", "value2");
+        map.put("key3", "value3");
+        
+        Iterator<String> iterator = map.keySet().iterator();
+        while(iterator.hasNext()){ 
+            iterator.next();
+            map.put("key4", "value4");
+        }        
+    }
+
+    @Test
+    public void givenHashtable_whenModifyUnderlyingCollection_thenItHasNoEffectOnIteratedCollection() {
+        Hashtable<String, String> table = new Hashtable<String, String>();        
+        table.put("key1", "value1");
+        table.put("key2", "value2");
+        
+        List<String> keysSelected = Lists.newArrayList(); 
+        Enumeration<String> keys = table.keys();
+        while (keys.hasMoreElements()) {
+            String key = keys.nextElement();
+            keysSelected.add(key);
+            
+            if (key.equals("key1")) {
+                table.put("key3", "value3");
+            }
+        }
+        
+        assertEquals(2, keysSelected.size());
+    }
+    
+    // synchronized map
+    @Test
+    public void givenHashmap_thenCreateSynchronizedMap() {
+        HashMap<String, String> map = new HashMap<String, String>();
+        map.put("key1", "value1");
+        map.put("key2", "value2");
+        map.put("key3", "value3");
+        
+        Set<Entry<String, String>> set = map.entrySet();
+        synchronized (map) {
+            Iterator<Entry<String, String>> it = set.iterator();
+            while(it.hasNext()) {
+                Map.Entry<String, String> elem = (Map.Entry<String, String>)it.next();
+             }            
+        }
+        
+        Map<String, String> syncMap = Collections.synchronizedMap(map);
+    }
+}

core-java-modules/core-java-collections-3/src/test/java/com/baeldung/collections/iterators/IteratorsUnitTest.java

@@ -0,0 +1,40 @@
+package com.baeldung.collections.iterators;
+
+import static com.baeldung.collections.iterators.Iterators.failFast1;
+import static com.baeldung.collections.iterators.Iterators.failFast2;
+import static com.baeldung.collections.iterators.Iterators.failSafe1;
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+import java.util.ConcurrentModificationException;
+
+import org.junit.Test;
+
+/**
+ * Source code https://github.com/eugenp/tutorials
+ *
+ * @author Santosh Thakur
+ */
+
+public class IteratorsUnitTest {
+
+    @Test
+    public void whenFailFast_ThenThrowsException() {
+        assertThatThrownBy(() -> {
+            failFast1();
+        }).isInstanceOf(ConcurrentModificationException.class);
+    }
+
+    @Test
+    public void whenFailFast_ThenThrowsExceptionInSecondIteration() {
+        assertThatThrownBy(() -> {
+            failFast2();
+        }).isInstanceOf(ConcurrentModificationException.class);
+    }
+
+    @Test
+    public void whenFailSafe_ThenDoesNotThrowException() {
+        assertThat(failSafe1()).isGreaterThanOrEqualTo(0);
+    }
+
+}