Split or move core-java-collections module (#7842)
This commit is contained in:
Catalin Burcea
committed by
Josh Cummings
Josh Cummings
parent
957ad4587c
commit
0677a06271
11
core-java-modules/core-java-collections-3/README.md
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11
core-java-modules/core-java-collections-3/README.md
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=========
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## Core Java Collections Cookbooks and Examples
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### Relevant Articles:
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- [Time Comparison of Arrays.sort(Object[]) and Arrays.sort(int[])](https://www.baeldung.com/arrays-sortobject-vs-sortint)
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- [Java ArrayList vs Vector](https://www.baeldung.com/java-arraylist-vs-vector)
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- [Differences Between HashMap and Hashtable](https://www.baeldung.com/hashmap-hashtable-differences)
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- [Differences Between Collection.clear() and Collection.removeAll()](https://www.baeldung.com/java-collection-clear-vs-removeall)
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- [Performance of contains() in a HashSet vs ArrayList](https://www.baeldung.com/java-hashset-arraylist-contains-performance)
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- [Fail-Safe Iterator vs Fail-Fast Iterator](https://www.baeldung.com/java-fail-safe-vs-fail-fast-iterator)
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34
core-java-modules/core-java-collections-3/pom.xml
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34
core-java-modules/core-java-collections-3/pom.xml
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<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
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<modelVersion>4.0.0</modelVersion>
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<artifactId>core-java-collections-3</artifactId>
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<version>0.1.0-SNAPSHOT</version>
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<name>core-java-collections-3</name>
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<packaging>jar</packaging>
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<parent>
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<groupId>com.baeldung</groupId>
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<artifactId>parent-java</artifactId>
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<version>0.0.1-SNAPSHOT</version>
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<relativePath>../../parent-java</relativePath>
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</parent>
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<dependencies>
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<dependency>
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<groupId>org.openjdk.jmh</groupId>
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<artifactId>jmh-core</artifactId>
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<version>${openjdk.jmh.version}</version>
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</dependency>
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<dependency>
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<groupId>org.assertj</groupId>
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<artifactId>assertj-core</artifactId>
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<version>${assertj.version}</version>
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<scope>test</scope>
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</dependency>
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</dependencies>
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<properties>
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<openjdk.jmh.version>1.19</openjdk.jmh.version>
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<assertj.version>3.11.1</assertj.version>
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</properties>
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</project>
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package com.baeldung.collections.arraylistvsvector;
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import org.openjdk.jmh.annotations.*;
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import org.openjdk.jmh.runner.Runner;
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import org.openjdk.jmh.runner.options.Options;
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import org.openjdk.jmh.runner.options.OptionsBuilder;
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import java.util.*;
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import java.util.concurrent.TimeUnit;
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@BenchmarkMode(Mode.AverageTime)
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@OutputTimeUnit(TimeUnit.NANOSECONDS)
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@Warmup(iterations = 10)
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public class ArrayListBenchmark {
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@State(Scope.Thread)
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public static class MyState {
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List<Employee> employeeList = new ArrayList<>();
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Vector<Employee> employeeVector = new Vector<>();
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//LinkedList<Employee> employeeList = new LinkedList<>();
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long iterations = 100000;
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Employee employee = new Employee(100L, "Harry");
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int employeeIndex = -1;
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@Setup(Level.Trial)
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public void setUp() {
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for (long i = 0; i < iterations; i++) {
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employeeList.add(new Employee(i, "John"));
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employeeVector.add(new Employee(i, "John"));
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}
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employeeList.add(employee);
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employeeVector.add(employee);
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employeeIndex = employeeList.indexOf(employee);
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}
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}
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@Benchmark
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public void testAddAt(ArrayListBenchmark.MyState state) {
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state.employeeList.add((int) (state.iterations), new Employee(state.iterations, "John"));
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}
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@Benchmark
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public boolean testContains(ArrayListBenchmark.MyState state) {
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return state.employeeList.contains(state.employee);
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}
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@Benchmark
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public boolean testContainsVector(ArrayListBenchmark.MyState state) {
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return state.employeeVector.contains(state.employee);
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}
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@Benchmark
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public int testIndexOf(ArrayListBenchmark.MyState state) {
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return state.employeeList.indexOf(state.employee);
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}
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@Benchmark
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public Employee testGet(ArrayListBenchmark.MyState state) {
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return state.employeeList.get(state.employeeIndex);
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}
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@Benchmark
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public Employee testVectorGet(ArrayListBenchmark.MyState state) {
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return state.employeeVector.get(state.employeeIndex);
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}
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@Benchmark
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public boolean testRemove(ArrayListBenchmark.MyState state) {
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return state.employeeList.remove(state.employee);
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}
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@Benchmark
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public void testAdd(ArrayListBenchmark.MyState state) {
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state.employeeList.add(new Employee(state.iterations + 1, "John"));
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}
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public static void main(String[] args) throws Exception {
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Options options = new OptionsBuilder()
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.include(ArrayListBenchmark.class.getSimpleName()).threads(3)
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.forks(1).shouldFailOnError(true)
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.shouldDoGC(true)
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.jvmArgs("-server").build();
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new Runner(options).run();
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}
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}
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@@ -0,0 +1,55 @@
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package com.baeldung.collections.arraylistvsvector;
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public class Employee {
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private Long id;
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private String name;
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public Employee(Long id, String name) {
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this.name = name;
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this.id = id;
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}
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public Long getId() {
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return id;
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}
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public void setId(Long id) {
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this.id = id;
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}
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public String getName() {
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return name;
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}
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public void setName(String name) {
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this.name = name;
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}
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@Override
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public boolean equals(Object o) {
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if (this == o) return true;
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if (o == null || getClass() != o.getClass()) return false;
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Employee employee = (Employee) o;
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if (!id.equals(employee.id)) return false;
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return name.equals(employee.name);
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}
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@Override
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public int hashCode() {
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int result = id.hashCode();
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result = 31 * result + name.hashCode();
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return result;
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}
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@Override
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public String toString() {
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return "Employee{" +
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"id=" + id +
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", name='" + name + '\'' +
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'}';
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}
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}
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@@ -0,0 +1,27 @@
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package com.baeldung.collections.arraylistvsvector;
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import java.util.Enumeration;
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import java.util.Iterator;
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import java.util.Vector;
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public class VectorExample {
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public static void main(String[] args) {
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Vector<String> vector = new Vector<>();
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vector.add("baeldung");
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vector.add("Vector");
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vector.add("example");
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Enumeration e = vector.elements();
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while(e.hasMoreElements()){
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System.out.println(e.nextElement());
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}
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Iterator<String> iterator = vector.iterator();
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while (iterator.hasNext()) {
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System.out.println(iterator.next());
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}
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}
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}
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@@ -0,0 +1,59 @@
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package com.baeldung.collections.containsperformance;
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import org.openjdk.jmh.annotations.*;
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import org.openjdk.jmh.runner.Runner;
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import org.openjdk.jmh.runner.options.Options;
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import org.openjdk.jmh.runner.options.OptionsBuilder;
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import java.util.ArrayList;
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import java.util.HashSet;
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import java.util.List;
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import java.util.Set;
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import java.util.concurrent.TimeUnit;
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@BenchmarkMode(Mode.AverageTime)
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@OutputTimeUnit(TimeUnit.NANOSECONDS)
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@Warmup(iterations = 5)
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public class CollectionsBenchmark {
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@State(Scope.Thread)
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public static class MyState {
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private Set<Employee> employeeSet = new HashSet<>();
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private List<Employee> employeeList = new ArrayList<>();
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private long iterations = 10000;
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private Employee employee = new Employee(100L, "Harry");
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@Setup(Level.Trial)
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public void setUp() {
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for (long i = 0; i < iterations; i++) {
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employeeSet.add(new Employee(i, "John"));
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employeeList.add(new Employee(i, "John"));
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}
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employeeList.add(employee);
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employeeSet.add(employee);
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}
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}
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@Benchmark
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public boolean testArrayList(MyState state) {
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return state.employeeList.contains(state.employee);
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}
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@Benchmark
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public boolean testHashSet(MyState state) {
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return state.employeeSet.contains(state.employee);
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}
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public static void main(String[] args) throws Exception {
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Options options = new OptionsBuilder()
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.include(CollectionsBenchmark.class.getSimpleName()).threads(1)
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.forks(1).shouldFailOnError(true)
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.shouldDoGC(true)
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.jvmArgs("-server").build();
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new Runner(options).run();
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}
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}
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@@ -0,0 +1,55 @@
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package com.baeldung.collections.containsperformance;
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public class Employee {
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private Long id;
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private String name;
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public Employee(Long id, String name) {
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this.name = name;
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this.id = id;
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}
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public Long getId() {
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return id;
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}
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public void setId(Long id) {
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this.id = id;
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}
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public String getName() {
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return name;
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}
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public void setName(String name) {
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this.name = name;
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}
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@Override
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public boolean equals(Object o) {
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if (this == o) return true;
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if (o == null || getClass() != o.getClass()) return false;
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Employee employee = (Employee) o;
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if (!id.equals(employee.id)) return false;
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return name.equals(employee.name);
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}
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@Override
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public int hashCode() {
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int result = id.hashCode();
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result = 31 * result + name.hashCode();
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return result;
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}
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@Override
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public String toString() {
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return "Employee{" +
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"id=" + id +
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", name='" + name + '\'' +
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'}';
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}
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}
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@@ -0,0 +1,80 @@
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package com.baeldung.collections.iterators;
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import java.util.ArrayList;
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import java.util.Iterator;
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import java.util.concurrent.ConcurrentHashMap;
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/**
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* Source code https://github.com/eugenp/tutorials
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*
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* @author Santosh Thakur
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*/
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public class Iterators {
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public static int failFast1() {
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ArrayList<Integer> numbers = new ArrayList<>();
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numbers.add(10);
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numbers.add(20);
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numbers.add(30);
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numbers.add(40);
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Iterator<Integer> iterator = numbers.iterator();
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while (iterator.hasNext()) {
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Integer number = iterator.next();
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numbers.add(50);
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}
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return numbers.size();
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}
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public static int failFast2() {
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ArrayList<Integer> numbers = new ArrayList<>();
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numbers.add(10);
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numbers.add(20);
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numbers.add(30);
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numbers.add(40);
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Iterator<Integer> iterator = numbers.iterator();
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while (iterator.hasNext()) {
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if (iterator.next() == 30) {
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// will not throw Exception
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iterator.remove();
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}
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}
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System.out.println("using iterator's remove method = " + numbers);
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iterator = numbers.iterator();
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while (iterator.hasNext()) {
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if (iterator.next() == 40) {
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// will throw Exception on
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// next call of next() method
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numbers.remove(2);
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}
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}
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return numbers.size();
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}
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public static int failSafe1() {
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ConcurrentHashMap<String, Integer> map = new ConcurrentHashMap<>();
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map.put("First", 10);
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map.put("Second", 20);
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map.put("Third", 30);
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map.put("Fourth", 40);
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Iterator<String> iterator = map.keySet()
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.iterator();
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while (iterator.hasNext()) {
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String key = iterator.next();
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map.put("Fifth", 50);
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}
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return map.size();
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}
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}
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@@ -0,0 +1,51 @@
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package com.baeldung.collections.sortingcomparison;
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import java.util.Arrays;
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import java.util.concurrent.TimeUnit;
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import org.openjdk.jmh.annotations.Benchmark;
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import org.openjdk.jmh.annotations.BenchmarkMode;
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import org.openjdk.jmh.annotations.Measurement;
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import org.openjdk.jmh.annotations.Mode;
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import org.openjdk.jmh.annotations.OutputTimeUnit;
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import org.openjdk.jmh.annotations.Scope;
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import org.openjdk.jmh.annotations.State;
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import org.openjdk.jmh.annotations.Warmup;
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import org.openjdk.jmh.runner.Runner;
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import org.openjdk.jmh.runner.options.Options;
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import org.openjdk.jmh.runner.options.OptionsBuilder;
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@BenchmarkMode(Mode.AverageTime)
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@OutputTimeUnit(TimeUnit.MILLISECONDS)
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@Measurement(batchSize = 100000, iterations = 10)
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@Warmup(batchSize = 100000, iterations = 10)
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public class ArraySortBenchmark {
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@State(Scope.Thread)
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public static class Initialize {
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Integer[] numbers = { -769214442, -1283881723, 1504158300, -1260321086, -1800976432, 1278262737, 1863224321, 1895424914, 2062768552, -1051922993, 751605209, -1500919212, 2094856518, -1014488489, -931226326, -1677121986, -2080561705, 562424208, -1233745158, 41308167 };
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int[] primitives = { -769214442, -1283881723, 1504158300, -1260321086, -1800976432, 1278262737, 1863224321, 1895424914, 2062768552, -1051922993, 751605209, -1500919212, 2094856518, -1014488489, -931226326, -1677121986, -2080561705, 562424208, -1233745158, 41308167 };
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}
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@Benchmark
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public Integer[] benchmarkArraysIntegerSort(ArraySortBenchmark.Initialize state) {
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Arrays.sort(state.numbers);
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return state.numbers;
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}
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@Benchmark
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public int[] benchmarkArraysIntSort(ArraySortBenchmark.Initialize state) {
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Arrays.sort(state.primitives);
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return state.primitives;
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}
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public static void main(String[] args) throws Exception {
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Options options = new OptionsBuilder()
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.include(ArraySortBenchmark.class.getSimpleName()).threads(1)
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.forks(1).shouldFailOnError(true)
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.shouldDoGC(true)
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.jvmArgs("-server").build();
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new Runner(options).run();
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}
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}
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@@ -0,0 +1,39 @@
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package com.baeldung.collections.sortingcomparison;
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import java.util.ArrayList;
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import java.util.Arrays;
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import java.util.Collections;
|
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import java.util.List;
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public class CollectionsSortCompare {
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public static void main(String[] args) {
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sortPrimitives();
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sortReferenceType();
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sortCollection();
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}
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private static void sortReferenceType() {
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Integer[] numbers = {5, 22, 10, 0};
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Arrays.sort(numbers);
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System.out.println(Arrays.toString(numbers));
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}
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private static void sortCollection() {
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List<Integer> numbersList = new ArrayList<>();
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numbersList.add(5);
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numbersList.add(22);
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numbersList.add(10);
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numbersList.add(0);
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Collections.sort(numbersList);
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numbersList.forEach(System.out::print);
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}
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private static void sortPrimitives() {
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int[] numbers = {5, 22, 10, 0};
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Arrays.sort(numbers);
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System.out.println(Arrays.toString(numbers));
|
||||
}
|
||||
}
|
||||
@@ -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);
|
||||
}
|
||||
|
||||
}
|
||||
@@ -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);
|
||||
}
|
||||
}
|
||||
@@ -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);
|
||||
}
|
||||
|
||||
}
|
||||
Reference in New Issue
Block a user