BAEL-5167: add sample key implementations and test the correct functionality and the performance of those keys in a HashMap (#11260)
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Ralf Ueberfuhr
GitHub
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## Java Collections Cookbooks and Examples
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This module contains articles about Map data structures in Java.
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### Relevant Articles:
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- [Using a Custom Class as a Key in a Java HashMap](https://www.baeldung.com/custom-key-hashmap)
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<?xml version="1.0" encoding="UTF-8"?>
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<project xmlns="http://maven.apache.org/POM/4.0.0"
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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-maps-4</artifactId>
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<version>0.1.0-SNAPSHOT</version>
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<name>core-java-collections-maps-4</name>
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<packaging>jar</packaging>
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<parent>
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<groupId>com.baeldung.core-java-modules</groupId>
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<artifactId>core-java-modules</artifactId>
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<version>0.0.1-SNAPSHOT</version>
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<relativePath>../pom.xml</relativePath>
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</parent>
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<build>
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<pluginManagement>
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<plugins>
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<plugin>
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<groupId>org.apache.maven.plugins</groupId>
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<artifactId>maven-surefire-plugin</artifactId>
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<version>3.0.0-M5</version>
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<configuration>
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<!-- those tests are not made for CI purposes, but for manual testing -->
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<groups>!performance</groups>
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</configuration>
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</plugin>
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</plugins>
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</pluginManagement>
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</build>
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</project>
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package com.baeldung.maps;
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import java.util.Objects;
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public class CoordinateKey {
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private final int x;
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private final int y;
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private final int hashCode;
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public CoordinateKey(int x, int y) {
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this.x = x;
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this.y = y;
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this.hashCode = Objects.hash(x, y);
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}
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public int getX() {
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return x;
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}
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public int getY() {
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return y;
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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)
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return true;
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if (o == null || getClass() != o.getClass())
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return false;
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CoordinateKey that = (CoordinateKey) o;
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return x == that.x && y == that.y;
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}
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@Override
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public int hashCode() {
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return this.hashCode;
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}
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}
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package com.baeldung.maps;
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import java.util.Objects;
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public class CoordinateMutableKey {
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private int x;
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private int y;
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public CoordinateMutableKey(int x, int y) {
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this.x = x;
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this.y = y;
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}
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public int getX() {
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return x;
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}
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public void setX(int x) {
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this.x = x;
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}
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public int getY() {
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return y;
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}
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public void setY(int y) {
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this.y = y;
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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)
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return true;
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if (o == null || getClass() != o.getClass())
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return false;
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CoordinateMutableKey that = (CoordinateMutableKey) o;
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return x == that.x && y == that.y;
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}
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@Override
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public int hashCode() {
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return Objects.hash(x, y);
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}
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}
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package com.baeldung.maps;
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public class CoordinateSlowKey extends CoordinateKey {
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public CoordinateSlowKey(int x, int y) {
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super(x, y);
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}
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@Override
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public int hashCode() {
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return 1;
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}
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}
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package com.baeldung.maps;
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import org.junit.jupiter.api.Tag;
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import org.junit.jupiter.api.Test;
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import java.awt.*;
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import java.util.HashMap;
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import java.util.Map;
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import static org.junit.jupiter.api.Assertions.assertEquals;
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import static org.junit.jupiter.api.Assertions.assertNotNull;
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public class CoordinateKeyUnitTest {
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private Map<CoordinateKey, Color> pixels = new HashMap<>();
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@Test
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void testOptimalKey() {
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// setup
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CoordinateKey coord = new CoordinateKey(1, 2);
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pixels.put(coord, Color.CYAN);
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// read out color correctly
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assertEquals(Color.CYAN, pixels.get(coord));
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}
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@Test
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void testSlowKey() {
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// setup
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CoordinateKey coord = new CoordinateSlowKey(1, 2);
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pixels.put(coord, Color.CYAN);
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// read out color correctly
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assertEquals(Color.CYAN, pixels.get(coord));
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}
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// Performance Test Parameters - change here
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private static final int MAX_X = 100;
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private static final int MAX_Y = 100;
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private static final int COUNT_OF_QUERIES = 1000;
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private static final int QUERY_X = 1;
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private static final int QUERY_Y = 1;
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@Tag("performance")
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@Test
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void testKeyPerformance() {
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// generate some sample keys and values
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for (int x = 0; x < MAX_X; x++) {
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for (int y = 0; y < MAX_Y; y++) {
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pixels.put(new CoordinateKey(x, y), new Color(x % 255, y % 255, (x + y) % 255));
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}
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}
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// read out multiple times and measure time
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CoordinateKey coord = new CoordinateKey(QUERY_X, QUERY_Y);
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long t1 = System.currentTimeMillis();
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for (int i = 0; i < COUNT_OF_QUERIES; i++) {
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assertNotNull(pixels.get(coord));
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}
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long t2 = System.currentTimeMillis();
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System.out.printf("Optimal key performance: %d ms%n", t2 - t1);
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}
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@Tag("performance")
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@Test
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void testSlowKeyPerformance() {
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// generate some sample keys and values
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for (int x = 0; x < MAX_X; x++) {
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for (int y = 0; y < MAX_Y; y++) {
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pixels.put(new CoordinateSlowKey(x, y), new Color(x % 255, y % 255, (x + y) % 255));
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}
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}
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// read out multiple times and measure time
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CoordinateKey coord = new CoordinateSlowKey(QUERY_X, QUERY_Y);
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long t1 = System.currentTimeMillis();
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for (int i = 0; i < COUNT_OF_QUERIES; i++) {
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assertNotNull(pixels.get(coord));
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}
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long t2 = System.currentTimeMillis();
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System.out.printf("Slow key performance: %d ms%n", t2 - t1);
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}
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}
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package com.baeldung.maps;
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import org.junit.jupiter.api.Test;
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import java.awt.*;
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import java.util.HashMap;
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import java.util.Map;
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import static org.junit.jupiter.api.Assertions.assertEquals;
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import static org.junit.jupiter.api.Assertions.assertNull;
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public class CoordinateMutableKeyUnitTest {
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@Test
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void testKeyMutable() {
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// setup
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Map<CoordinateMutableKey, Color> pixels = new HashMap<>();
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CoordinateMutableKey coord = new CoordinateMutableKey(1, 2);
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pixels.put(coord, Color.CYAN);
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// read out color correctly
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assertEquals(Color.CYAN, pixels.get(coord));
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// change key's hashcode should result in null value
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coord.setX(10);
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assertNull(pixels.get(coord));
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}
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}
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<module>core-java-collections-maps</module>
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<module>core-java-collections-maps-2</module>
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<module>core-java-collections-maps-3</module>
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<module>core-java-collections-maps-4</module>
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<module>core-java-concurrency-2</module>
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<module>core-java-concurrency-advanced</module>
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<module>core-java-concurrency-advanced-2</module>
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<junit-jupiter.version>5.6.2</junit-jupiter.version>
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</properties>
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</project>
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</project>
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