diff --git a/core-java-collections-map/README.md b/core-java-collections-map/README.md new file mode 100644 index 0000000000..da02928118 --- /dev/null +++ b/core-java-collections-map/README.md @@ -0,0 +1,6 @@ +========= + +## Core Java Collections 2 + +### Relevant Articles: +- Java - Copying a HashMap diff --git a/core-java-collections-map/pom.xml b/core-java-collections-map/pom.xml new file mode 100644 index 0000000000..8c0aef54bf --- /dev/null +++ b/core-java-collections-map/pom.xml @@ -0,0 +1,78 @@ + + 4.0.0 + core-java-collections-map + 0.1.0-SNAPSHOT + core-java-collections-map + jar + + + com.baeldung + parent-java + 0.0.1-SNAPSHOT + ../parent-java + + + + + org.apache.commons + commons-collections4 + ${commons-collections4.version} + + + org.apache.commons + commons-lang3 + ${commons-lang3.version} + + + org.eclipse.collections + eclipse-collections + ${eclipse.collections.version} + + + org.assertj + assertj-core + ${assertj.version} + test + + + org.junit.platform + junit-platform-runner + ${junit.platform.version} + test + + + org.openjdk.jmh + jmh-core + ${openjdk.jmh.version} + + + org.openjdk.jmh + jmh-generator-annprocess + ${openjdk.jmh.version} + + + org.apache.commons + commons-exec + ${commons-exec.version} + + + org.projectlombok + lombok + ${lombok.version} + provided + + + + + 1.19 + 1.2.0 + 3.8.1 + 4.1 + 4.01 + 1.7.0 + 3.11.1 + 7.1.0 + 1.3 + + diff --git a/core-java-collections-map/src/main/java/com/baeldung/copyinghashmap/CopyHashMap.java b/core-java-collections-map/src/main/java/com/baeldung/copyinghashmap/CopyHashMap.java new file mode 100644 index 0000000000..e1649f593c --- /dev/null +++ b/core-java-collections-map/src/main/java/com/baeldung/copyinghashmap/CopyHashMap.java @@ -0,0 +1,55 @@ +package com.baeldung.copyinghashmap; + +import java.util.HashMap; +import java.util.Map; +import java.util.Map.Entry; +import java.util.Set; +import java.util.stream.Collectors; + +import org.apache.commons.lang3.SerializationUtils; + +public class CopyHashMap { + + public static HashMap copyUsingConstructor(HashMap originalMap) { + return new HashMap(originalMap); + } + + public static HashMap copyUsingClone(HashMap originalMap) { + return (HashMap) originalMap.clone(); + } + + public static HashMap copyUsingPut(HashMap originalMap) { + HashMap shallowCopy = new HashMap(); + Set> entries = originalMap.entrySet(); + for(Map.Entry mapEntry: entries) { + shallowCopy.put(mapEntry.getKey(), mapEntry.getValue()); + } + + return shallowCopy; + } + + public static HashMap copyUsingPutAll(HashMap originalMap) { + HashMap shallowCopy = new HashMap(); + shallowCopy.putAll(originalMap); + + return shallowCopy; + } + + public static HashMap copyUsingJava8Stream(HashMap originalMap) { + Set> entries = originalMap.entrySet(); + HashMap shallowCopy = (HashMap) entries + .stream() + .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue)); + + return shallowCopy; + } + + public static HashMap shallowCopy(HashMap originalMap) { + return (HashMap) originalMap.clone(); + } + + public static HashMap deepCopy(HashMap originalMap) { + return SerializationUtils.clone(originalMap); + } + +} diff --git a/core-java-collections-map/src/test/java/com/baeldung/copyinghashmap/CopyHashMapUnitTest.java b/core-java-collections-map/src/test/java/com/baeldung/copyinghashmap/CopyHashMapUnitTest.java new file mode 100644 index 0000000000..400696d97a --- /dev/null +++ b/core-java-collections-map/src/test/java/com/baeldung/copyinghashmap/CopyHashMapUnitTest.java @@ -0,0 +1,77 @@ +package com.baeldung.copyinghashmap; + +import static org.assertj.core.api.Assertions.assertThat; + +import java.util.HashMap; +import java.util.Map; + +import org.junit.Test; + +import com.google.common.collect.ImmutableMap; + +public class CopyHashMapUnitTest { + + @Test + public void givenHashMap_whenShallowCopy_thenCopyisNotSameAsOriginal() { + + HashMap map = new HashMap<>(); + Employee emp1 = new Employee("John"); + Employee emp2 = new Employee("Norman"); + map.put("emp1",emp1); + map.put("emp2",emp2); + + HashMap shallowCopy = CopyHashMap.shallowCopy(map); + + assertThat(shallowCopy).isNotSameAs(map); + + } + + @Test + public void givenHashMap_whenShallowCopyModifyingOriginalObject_thenCopyShouldChange() { + + HashMap map = new HashMap<>(); + Employee emp1 = new Employee("John"); + Employee emp2 = new Employee("Norman"); + map.put("emp1",emp1); + map.put("emp2",emp2); + + HashMap shallowCopy = CopyHashMap.shallowCopy(map); + + emp1.setName("Johny"); + + assertThat(shallowCopy.get("emp1")).isEqualTo(map.get("emp1")); + + } + + @Test + public void givenHashMap_whenDeepCopyModifyingOriginalObject_thenCopyShouldNotChange() { + + HashMap map = new HashMap<>(); + Employee emp1 = new Employee("John"); + Employee emp2 = new Employee("Norman"); + map.put("emp1",emp1); + map.put("emp2",emp2); + HashMap deepCopy = CopyHashMap.deepCopy(map); + + emp1.setName("Johny"); + + assertThat(deepCopy.get("emp1")).isNotEqualTo(map.get("emp1")); + + } + + @Test + public void givenImmutableMap_whenCopyUsingGuava_thenCopyShouldNotChange() { + Employee emp1 = new Employee("John"); + Employee emp2 = new Employee("Norman"); + + Map map = ImmutableMap. builder() + .put("emp1",emp1) + .put("emp2",emp2) + .build(); + Map shallowCopy = ImmutableMap.copyOf(map); + + assertThat(shallowCopy).isSameAs(map); + + } + +} diff --git a/core-java-collections-map/src/test/java/com/baeldung/copyinghashmap/Employee.java b/core-java-collections-map/src/test/java/com/baeldung/copyinghashmap/Employee.java new file mode 100644 index 0000000000..b47fdc768e --- /dev/null +++ b/core-java-collections-map/src/test/java/com/baeldung/copyinghashmap/Employee.java @@ -0,0 +1,28 @@ +package com.baeldung.copyinghashmap; + +import java.io.Serializable; + +public class Employee implements Serializable{ + + private String name; + + public Employee(String name) { + super(); + this.name = name; + } + public String getName() { + return name; + } + + public void setName(String name) { + this.name = name; + } + + @Override + public String toString() { + return this.name; + } + +} + + diff --git a/pom.xml b/pom.xml index 7fb9ca351f..bdd8403231 100644 --- a/pom.xml +++ b/pom.xml @@ -385,6 +385,7 @@ core-java-arrays core-java-collections + core-java-collections-map core-java-collections-list core-java-concurrency-basic core-java-concurrency-collections @@ -1041,6 +1042,7 @@ core-java-arrays core-java-collections + core-java-collections-map core-java-collections-list core-java-concurrency-basic core-java-concurrency-collections