diff --git a/core-java-modules/core-java-collections-maps-4/pom.xml b/core-java-modules/core-java-collections-maps-4/pom.xml
index be467dd57b..e5afd87bbe 100644
--- a/core-java-modules/core-java-collections-maps-4/pom.xml
+++ b/core-java-modules/core-java-collections-maps-4/pom.xml
@@ -15,6 +15,16 @@
     </parent>
 
     <dependencies>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-collections4</artifactId>
+            <version>${commons-collections4.version}</version>
+        </dependency>
+        <dependency>
+            <groupId>com.google.guava</groupId>
+            <artifactId>guava</artifactId>
+            <version>${guava.version}</version>
+        </dependency>
         <dependency>
             <groupId>junit</groupId>
             <artifactId>junit</artifactId>
@@ -37,12 +47,23 @@
                 </plugin>
             </plugins>
         </pluginManagement>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <version>${maven-compiler-plugin.version}</version>
+                <configuration>
+                    <source>${maven.compiler.source}</source>
+                    <target>${maven.compiler.target}</target>
+                </configuration>
+            </plugin>
+        </plugins>
     </build>
 
     <properties>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
-        <maven.compiler.source>1.8</maven.compiler.source>
-        <maven.compiler.target>1.8</maven.compiler.target>
+        <maven.compiler.source>1.9</maven.compiler.source>
+        <maven.compiler.target>1.9</maven.compiler.target>
     </properties>
 
 </project>
\ No newline at end of file
diff --git a/core-java-modules/core-java-collections-maps-4/src/main/java/com/baeldung/entries/SimpleCustomKeyValue.java b/core-java-modules/core-java-collections-maps-4/src/main/java/com/baeldung/entries/SimpleCustomKeyValue.java
new file mode 100644
index 0000000000..b2925cd508
--- /dev/null
+++ b/core-java-modules/core-java-collections-maps-4/src/main/java/com/baeldung/entries/SimpleCustomKeyValue.java
@@ -0,0 +1,53 @@
+package com.baeldung.entries;
+
+import java.util.Map;
+import java.util.Objects;
+import java.util.StringJoiner;
+
+public class SimpleCustomKeyValue<K, V> implements Map.Entry<K, V> {
+
+    private final K key;
+    private V value;
+
+    public SimpleCustomKeyValue(K key, V value) {
+        this.key = key;
+        this.value = value;
+    }
+
+    @Override
+    public K getKey() {
+        return key;
+    }
+
+    @Override
+    public V getValue() {
+        return value;
+    }
+
+    @Override
+    public V setValue(V value) {
+        return this.value = value;
+    }
+
+    @Override
+    public boolean equals(Object o) {
+        if (this == o) {
+            return true;
+        }
+        if (o == null || getClass() != o.getClass()) {
+            return false;
+        }
+        SimpleCustomKeyValue<?, ?> that = (SimpleCustomKeyValue<?, ?>) o;
+        return Objects.equals(key, that.key) && Objects.equals(value, that.value);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(key, value);
+    }
+
+    @Override
+    public String toString() {
+        return new StringJoiner(", ", SimpleCustomKeyValue.class.getSimpleName() + "[", "]").add("key=" + key).add("value=" + value).toString();
+    }
+}
diff --git a/core-java-modules/core-java-collections-maps-4/src/test/java/com/baeldung/entries/EntriesExampleUnitTest.java b/core-java-modules/core-java-collections-maps-4/src/test/java/com/baeldung/entries/EntriesExampleUnitTest.java
new file mode 100644
index 0000000000..954a4a4f22
--- /dev/null
+++ b/core-java-modules/core-java-collections-maps-4/src/test/java/com/baeldung/entries/EntriesExampleUnitTest.java
@@ -0,0 +1,113 @@
+package com.baeldung.entries;
+
+import com.google.common.collect.Maps;
+import org.apache.commons.collections4.KeyValue;
+import org.apache.commons.collections4.keyvalue.DefaultMapEntry;
+import org.apache.commons.collections4.keyvalue.UnmodifiableMapEntry;
+import org.junit.jupiter.api.Test;
+
+import java.util.AbstractMap;
+import java.util.Map;
+import java.util.stream.Stream;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.tuple;
+
+public class EntriesExampleUnitTest {
+
+    @Test
+    public void givenEntries_whenVerifying_thenShouldContainKeyValues() {
+        AbstractMap.SimpleEntry<String, String> firstEntry = new AbstractMap.SimpleEntry<>("key1", "value1");
+        AbstractMap.SimpleEntry<String, String> secondEntry = new AbstractMap.SimpleEntry<>("key2", "value2");
+        AbstractMap.SimpleEntry<String, String> thirdEntry = new AbstractMap.SimpleEntry<>(firstEntry);
+        thirdEntry.setValue("a different value");
+
+        assertThat(Stream.of(firstEntry, secondEntry, thirdEntry))
+          .extracting("key", "value")
+          .containsExactly(
+            tuple("key1", "value1"),
+            tuple("key2", "value2"),
+            tuple("key1", "a different value"));
+    }
+
+    @Test
+    public void givenImmutableEntries_whenVerifying_thenShouldContainKeyValues() {
+        AbstractMap.SimpleImmutableEntry<String, String> firstEntry = new AbstractMap.SimpleImmutableEntry<>("key1", "value1");
+        AbstractMap.SimpleImmutableEntry<String, String> secondEntry = new AbstractMap.SimpleImmutableEntry<>("key2", "value2");
+        AbstractMap.SimpleImmutableEntry<String, String> thirdEntry = new AbstractMap.SimpleImmutableEntry<>(firstEntry);
+
+        assertThat(Stream.of(firstEntry, secondEntry, thirdEntry))
+          .extracting("key", "value")
+          .containsExactly(
+            tuple("key1", "value1"),
+            tuple("key2", "value2"),
+            tuple("key1", "value1"));
+    }
+
+    @Test
+    public void givenImmutableEntryUsingJava9_whenVerifying_thenShouldContainKeyValues() {
+        Map.Entry<String, String> entry = Map.entry("key", "value");
+
+        assertThat(entry.getKey())
+          .isEqualTo("key");
+        assertThat(entry.getValue())
+          .isEqualTo("value");
+    }
+
+
+    @Test
+    public void givenEntriesWithApacheCommons_whenVerifying_thenShouldContainKeyValues() {
+        Map.Entry<String, String> firstEntry = new DefaultMapEntry<>("key1", "value1");
+        KeyValue<String, String> secondEntry = new DefaultMapEntry<>("key2", "value2");
+
+        KeyValue<String, String> thirdEntry = new DefaultMapEntry<>(firstEntry);
+        KeyValue<String, String> fourthEntry = new DefaultMapEntry<>(secondEntry);
+
+        firstEntry.setValue("a different value");
+
+        assertThat(firstEntry)
+          .extracting("key", "value")
+          .containsExactly("key1", "a different value");
+
+        assertThat(Stream.of(secondEntry, thirdEntry, fourthEntry))
+          .extracting("key", "value")
+          .containsExactly(
+            tuple("key2", "value2"),
+            tuple("key1", "value1"),
+            tuple("key2", "value2"));
+    }
+
+    @Test
+    public void givenImmutableEntriesWithApacheCommons_whenVerifying_thenShouldContainKeyValues() {
+        Map.Entry<String, String> firstEntry = new UnmodifiableMapEntry<>("key1", "value1");
+        KeyValue<String, String> secondEntry = new UnmodifiableMapEntry<>("key2", "value2");
+
+        KeyValue<String, String> thirdEntry = new UnmodifiableMapEntry<>(firstEntry);
+        KeyValue<String, String> fourthEntry = new UnmodifiableMapEntry<>(secondEntry);
+
+        assertThat(firstEntry)
+          .extracting("key", "value")
+          .containsExactly("key1", "value1");
+
+        assertThat(Stream.of(secondEntry, thirdEntry, fourthEntry))
+          .extracting("key", "value")
+          .containsExactly(
+            tuple("key2", "value2"),
+            tuple("key1", "value1"),
+            tuple("key2", "value2"));
+    }
+
+
+    @Test
+    public void givenImmutableEntriesWithGuava_whenVerifying_thenShouldContainKeyValues() {
+        Map.Entry<String, String> firstEntry = Maps.immutableEntry("key1", "value1");
+        Map.Entry<String, String> secondEntry = Maps.immutableEntry("key2", "value2");
+
+        assertThat(Stream.of(firstEntry, secondEntry))
+          .extracting("key", "value")
+          .containsExactly(
+            tuple("key1", "value1"),
+            tuple("key2", "value2"));
+    }
+
+}
diff --git a/core-java-modules/core-java-collections-maps-4/src/test/java/com/baeldung/entries/SimpleCustomKeyValueUnitTest.java b/core-java-modules/core-java-collections-maps-4/src/test/java/com/baeldung/entries/SimpleCustomKeyValueUnitTest.java
new file mode 100644
index 0000000000..d055bb1653
--- /dev/null
+++ b/core-java-modules/core-java-collections-maps-4/src/test/java/com/baeldung/entries/SimpleCustomKeyValueUnitTest.java
@@ -0,0 +1,31 @@
+package com.baeldung.entries;
+
+import com.google.common.collect.ImmutableMap;
+import org.junit.jupiter.api.Test;
+
+import java.util.Map;
+import java.util.stream.Stream;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.tuple;
+
+class SimpleCustomKeyValueUnitTest {
+
+
+    @Test
+    public void givenModifiableEntries_whenVerifying_thenShouldContainKeyValues() {
+        Map.Entry<String, String> firstEntry = new SimpleCustomKeyValue<>("key1", "value1");
+
+        Map.Entry<String, String> secondEntry = new SimpleCustomKeyValue<>("key2", "value2");
+        secondEntry.setValue("different value");
+
+        Map<String, String> map = Map.ofEntries(firstEntry, secondEntry);
+
+        assertThat(map)
+          .isEqualTo(ImmutableMap.<String,String>builder()
+            .put("key1", "value1")
+            .put("key2", "different value")
+            .build());
+    }
+
+}
\ No newline at end of file
diff --git a/core-java-modules/pom.xml b/core-java-modules/pom.xml
index a25cf11454..60319b4de4 100644
--- a/core-java-modules/pom.xml
+++ b/core-java-modules/pom.xml
@@ -38,7 +38,6 @@
         <module>core-java-collections-maps</module>
         <module>core-java-collections-maps-2</module>
         <module>core-java-collections-maps-3</module>
-        <module>core-java-collections-maps-4</module>
         <module>core-java-concurrency-2</module>
         <module>core-java-concurrency-advanced</module>
         <module>core-java-concurrency-advanced-2</module>
diff --git a/pom.xml b/pom.xml
index cab9a34f02..3138b5c610 100644
--- a/pom.xml
+++ b/pom.xml
@@ -1329,6 +1329,7 @@
                  <!-- <module>core-java-modules/core-java-14</module> --> <!-- uses preview features, to be decided how to handle -->
                  <!-- <module>core-java-modules/core-java-15</module> --> <!-- uses preview features, to be decided how to handle -->
                  <module>core-java-modules/core-java-collections-set</module>
+                 <module>core-java-modules/core-java-collections-maps-4</module>
                  <module>core-java-modules/core-java-date-operations-1</module>
                  <module>core-java-modules/core-java-datetime-conversion</module>
                  <module>core-java-modules/core-java-datetime-string</module>
@@ -1387,6 +1388,7 @@
                 <!-- <module>core-java-modules/core-java-14</module> --> <!-- uses preview features, to be decided how to handle -->
                 <!-- <module>core-java-modules/core-java-15</module> --> <!-- uses preview features, to be decided how to handle -->
                 <module>core-java-modules/core-java-collections-set</module>
+                <module>core-java-modules/core-java-collections-maps-4</module>
                 <module>core-java-modules/core-java-date-operations-1</module>
                 <module>core-java-modules/core-java-datetime-conversion</module>
                 <module>core-java-modules/core-java-datetime-string</module>