Source Code for BAEL-2534 : Determine if all elements are the same in a Java list

core-java-collections-list/pom.xml

@@ -36,12 +36,6 @@
             <version>${lombok.version}</version>
             <scope>provided</scope>
         </dependency>
-        <dependency>
-            <groupId>org.junit.jupiter</groupId>
-            <artifactId>junit-jupiter-api</artifactId>
-            <version>${junit-jupiter.version}</version>
-            <scope>test</scope>
-        </dependency>
     </dependencies>
 
     <properties>
@@ -50,6 +44,5 @@
         <avaitility.version>1.7.0</avaitility.version>
         <assertj.version>3.11.1</assertj.version>
         <lombok.version>1.16.12</lombok.version>
-        <junit-jupiter.version>5.0.0-M4</junit-jupiter.version>
     </properties>
 </project>

core-java-collections-list/src/main/java/com/baeldung/allequalelements/VerifyAllEqualListElements.java

@@ -1,5 +1,7 @@
 package com.baeldung.allequalelements;
 
+import java.util.Collections;
+import java.util.HashSet;
 import java.util.List;
 import org.apache.commons.collections4.IterableUtils;
 import com.google.common.base.Predicate;
@@ -9,21 +11,32 @@ public class VerifyAllEqualListElements {
 
     public boolean verifyAllEqualUsingALoop(List<String> list) {
         for (String s : list) {
-            if(!s.equals(list.get(0)))
+            if (!s.equals(list.get(0)))
                 return false;
         }
         return true;
     }
 
+    public boolean verifyAllEqualUsingHashSet(List<String> list) {
+        return new HashSet<String>(list).size() <= 1;
+    }
+
+    public boolean verifyAllEqualUsingFrequency(List<String> list) {
+        return list.isEmpty() || Collections.frequency(list, list.get(0)) == list.size();
+    }
+
     public boolean verifyAllEqualUsingStream(List<String> list) {
-          return list.stream().distinct().limit(2).count() <= 1;
+        return list.stream()
+            .distinct()
+            .limit(2)
+            .count() <= 1;
     }
 
     public boolean verifyAllEqualAnotherUsingStream(List<String> list) {
-        return list.isEmpty() || list.stream().allMatch(list.get(0)::equals);
+        return list.isEmpty() || list.stream()
+            .allMatch(list.get(0)::equals);
     }
 
-
     public boolean verifyAllEqualUsingGuava(List<String> list) {
         return Iterables.all(list, new Predicate<String>() {
             public boolean apply(String s) {

core-java-collections-list/src/test/java/com/baeldung/allequalelements/VerifyAllEqualListElementsUnitTest.java

@@ -2,6 +2,7 @@ package com.baeldung.allequalelements;
 
 import org.junit.Test;
 import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.List;
 import static org.junit.Assert.assertFalse;
 import static org.junit.jupiter.api.Assertions.assertTrue;
@@ -10,30 +11,17 @@ public class VerifyAllEqualListElementsUnitTest {
 
     private static List<String> distinctList = new ArrayList<>();
 
-    static {
-        distinctList.add(new String("Jack"));
-        distinctList.add(new String("James"));
-        distinctList.add(new String("Sam"));
-    }
-
     private static List<String> notAllEqualList = new ArrayList<>();
 
-    static {
-        notAllEqualList.add(new String("Jack"));
-        notAllEqualList.add(new String("James"));
-        notAllEqualList.add(new String("Sam"));
-        notAllEqualList.add(new String("James"));
-    }
-
     private static List<String> emptyList = new ArrayList<>();
 
     private static List<String> allEqualList = new ArrayList<>();
 
     static {
-        allEqualList.add(new String("Jack"));
+        distinctList = Arrays.asList("Jack", "James", "Sam");
-        allEqualList.add(new String("Jack"));
+        notAllEqualList = Arrays.asList("Jack", "James", "Sam", "James");
-        allEqualList.add(new String("Jack"));
+        emptyList = Arrays.asList();
-        allEqualList.add(new String("Jack"));
+        allEqualList = Arrays.asList("Jack", "Jack", "Jack", "Jack");
     }
 
     private static VerifyAllEqualListElements verifyAllEqualListElements = new VerifyAllEqualListElements();
@@ -66,6 +54,62 @@ public class VerifyAllEqualListElementsUnitTest {
         assertTrue(allEqual);
     }
 
+    @Test
+    public void verifyAllEqualUsingHashSet_whenUsingDistinctList_thenReturnFalse() {
+        boolean allEqual = verifyAllEqualListElements.verifyAllEqualUsingHashSet(distinctList);
+
+        assertFalse(allEqual);
+    }
+
+    @Test
+    public void verifyAllEqualUsingHashSet_whenNotAllEqualList_thenReturnFalse() {
+        boolean allEqual = verifyAllEqualListElements.verifyAllEqualUsingHashSet(notAllEqualList);
+
+        assertFalse(allEqual);
+    }
+
+    @Test
+    public void verifyAllEqualUsingHashSet_whenEmptyList_thenReturnTrue() {
+        boolean allEqual = verifyAllEqualListElements.verifyAllEqualUsingHashSet(emptyList);
+
+        assertTrue(allEqual);
+    }
+
+    @Test
+    public void verifyAllEqualUsingHashSet_whenAllEqualList_thenReturnTrue() {
+        boolean allEqual = verifyAllEqualListElements.verifyAllEqualUsingHashSet(allEqualList);
+
+        assertTrue(allEqual);
+    }
+
+    @Test
+    public void verifyAllEqualUsingFrequency_whenUsingDistinctList_thenReturnFalse() {
+        boolean allEqual = verifyAllEqualListElements.verifyAllEqualUsingFrequency(distinctList);
+
+        assertFalse(allEqual);
+    }
+
+    @Test
+    public void verifyAllEqualUsingFrequency_whenNotAllEqualList_thenReturnFalse() {
+        boolean allEqual = verifyAllEqualListElements.verifyAllEqualUsingFrequency(notAllEqualList);
+
+        assertFalse(allEqual);
+    }
+
+    @Test
+    public void verifyAllEqualUsingFrequency_whenEmptyList_thenReturnTrue() {
+        boolean allEqual = verifyAllEqualListElements.verifyAllEqualUsingFrequency(emptyList);
+
+        assertTrue(allEqual);
+    }
+
+    @Test
+    public void verifyAllEqualUsingFrequency_whenAllEqualList_thenReturnTrue() {
+        boolean allEqual = verifyAllEqualListElements.verifyAllEqualUsingFrequency(allEqualList);
+
+        assertTrue(allEqual);
+    }
+
     @Test
     public void verifyAllEqualUsingStream_whenUsingDistinctList_thenReturnFalse() {
         boolean allEqual = verifyAllEqualListElements.verifyAllEqualUsingStream(distinctList);
@@ -122,7 +166,6 @@ public class VerifyAllEqualListElementsUnitTest {
         assertTrue(allEqual);
     }
 
-
     @Test
     public void verifyAllEqualUsingGuava_whenUsingDistinctList_thenReturnFalse() {
         boolean allEqual = verifyAllEqualListElements.verifyAllEqualUsingGuava(distinctList);