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

core-java-collections-list/pom.xml

@@ -36,6 +36,12 @@
             <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>
@@ -44,5 +50,6 @@
         <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

@@ -0,0 +1,43 @@
+package com.baeldung.allequalelements;
+
+import java.util.List;
+import org.apache.commons.collections4.IterableUtils;
+import com.google.common.base.Predicate;
+import com.google.common.collect.Iterables;
+
+public class VerifyAllEqualListElements {
+
+    public boolean verifyAllEqualUsingALoop(List<String> list) {
+        for (String s : list) {
+            if(!s.equals(list.get(0)))
+                return false;
+        }
+        return true;
+    }
+
+    public boolean verifyAllEqualUsingStream(List<String> list) {
+          return list.stream().distinct().limit(2).count() <= 1;
+    }
+
+    public boolean verifyAllEqualAnotherUsingStream(List<String> list) {
+        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) {
+                return s.equals(list.get(0));
+            }
+        });
+    }
+
+    public boolean verifyAllEqualUsingApacheCommon(List<String> list) {
+        return IterableUtils.matchesAll(list, new org.apache.commons.collections4.Predicate<String>() {
+            public boolean evaluate(String s) {
+                return s.equals(list.get(0));
+            }
+        });
+    }
+
+}

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

@@ -0,0 +1,181 @@
+package com.baeldung.allequalelements;
+
+import org.junit.Test;
+import java.util.ArrayList;
+import java.util.List;
+import static org.junit.Assert.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+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"));
+        allEqualList.add(new String("Jack"));
+        allEqualList.add(new String("Jack"));
+        allEqualList.add(new String("Jack"));
+    }
+
+    private static VerifyAllEqualListElements verifyAllEqualListElements = new VerifyAllEqualListElements();
+
+    @Test
+    public void verifyAllEqualUsingALoop_whenUsingDistinctList_thenReturnFalse() {
+        boolean allEqual = verifyAllEqualListElements.verifyAllEqualUsingALoop(distinctList);
+
+        assertFalse(allEqual);
+    }
+
+    @Test
+    public void verifyAllEqualUsingALoop_whenNotAllEqualList_thenReturnFalse() {
+        boolean allEqual = verifyAllEqualListElements.verifyAllEqualUsingALoop(notAllEqualList);
+
+        assertFalse(allEqual);
+    }
+
+    @Test
+    public void verifyAllEqualUsingALoop_whenEmptyList_thenReturnTrue() {
+        boolean allEqual = verifyAllEqualListElements.verifyAllEqualUsingALoop(emptyList);
+
+        assertTrue(allEqual);
+    }
+
+    @Test
+    public void verifyAllEqualUsingALoop_whenAllEqualList_thenReturnTrue() {
+        boolean allEqual = verifyAllEqualListElements.verifyAllEqualUsingALoop(allEqualList);
+
+        assertTrue(allEqual);
+    }
+
+    @Test
+    public void verifyAllEqualUsingStream_whenUsingDistinctList_thenReturnFalse() {
+        boolean allEqual = verifyAllEqualListElements.verifyAllEqualUsingStream(distinctList);
+
+        assertFalse(allEqual);
+    }
+
+    @Test
+    public void verifyAllEqualUsingStream_whenNotAllEqualList_thenReturnFalse() {
+        boolean allEqual = verifyAllEqualListElements.verifyAllEqualUsingStream(notAllEqualList);
+
+        assertFalse(allEqual);
+    }
+
+    @Test
+    public void verifyAllEqualUsingStream_whenEmptyList_thenReturnTrue() {
+        boolean allEqual = verifyAllEqualListElements.verifyAllEqualUsingStream(emptyList);
+
+        assertTrue(allEqual);
+    }
+
+    @Test
+    public void verifyAllEqualUsingStream_whenAllEqualList_thenReturnTrue() {
+        boolean allEqual = verifyAllEqualListElements.verifyAllEqualUsingStream(allEqualList);
+
+        assertTrue(allEqual);
+    }
+
+    @Test
+    public void verifyAllEqualAnotherUsingStream_whenUsingDistinctList_thenReturnFalse() {
+        boolean allEqual = verifyAllEqualListElements.verifyAllEqualAnotherUsingStream(distinctList);
+
+        assertFalse(allEqual);
+    }
+
+    @Test
+    public void verifyAllEqualAnotherUsingStream_whenNotAllEqualList_thenReturnFalse() {
+        boolean allEqual = verifyAllEqualListElements.verifyAllEqualAnotherUsingStream(notAllEqualList);
+
+        assertFalse(allEqual);
+    }
+
+    @Test
+    public void verifyAllEqualAnotherUsingStream_whenEmptyList_thenReturnTrue() {
+        boolean allEqual = verifyAllEqualListElements.verifyAllEqualAnotherUsingStream(emptyList);
+
+        assertTrue(allEqual);
+    }
+
+    @Test
+    public void verifyAllEqualAnotherUsingStream_whenAllEqualList_thenReturnTrue() {
+        boolean allEqual = verifyAllEqualListElements.verifyAllEqualAnotherUsingStream(allEqualList);
+
+        assertTrue(allEqual);
+    }
+
+
+    @Test
+    public void verifyAllEqualUsingGuava_whenUsingDistinctList_thenReturnFalse() {
+        boolean allEqual = verifyAllEqualListElements.verifyAllEqualUsingGuava(distinctList);
+
+        assertFalse(allEqual);
+    }
+
+    @Test
+    public void verifyAllEqualUsingGuava_whenNotAllEqualList_thenReturnFalse() {
+        boolean allEqual = verifyAllEqualListElements.verifyAllEqualUsingGuava(notAllEqualList);
+
+        assertFalse(allEqual);
+    }
+
+    @Test
+    public void verifyAllEqualUsingGuava_whenEmptyList_thenReturnTrue() {
+        boolean allEqual = verifyAllEqualListElements.verifyAllEqualUsingGuava(emptyList);
+
+        assertTrue(allEqual);
+    }
+
+    @Test
+    public void verifyAllEqualUsingGuava_whenAllEqualList_thenReturnTrue() {
+        boolean allEqual = verifyAllEqualListElements.verifyAllEqualUsingGuava(allEqualList);
+
+        assertTrue(allEqual);
+    }
+
+    @Test
+    public void verifyAllEqualUsingApacheCommon_whenUsingDistinctList_thenReturnFalse() {
+        boolean allEqual = verifyAllEqualListElements.verifyAllEqualUsingApacheCommon(distinctList);
+
+        assertFalse(allEqual);
+    }
+
+    @Test
+    public void verifyAllEqualUsingApacheCommon_whenNotAllEqualList_thenReturnFalse() {
+        boolean allEqual = verifyAllEqualListElements.verifyAllEqualUsingApacheCommon(notAllEqualList);
+
+        assertFalse(allEqual);
+    }
+
+    @Test
+    public void verifyAllEqualUsingApacheCommon_whenEmptyList_thenReturnTrue() {
+        boolean allEqual = verifyAllEqualListElements.verifyAllEqualUsingApacheCommon(emptyList);
+
+        assertTrue(allEqual);
+    }
+
+    @Test
+    public void verifyAllEqualUsingApacheCommon_whenAllEqualList_thenReturnTrue() {
+        boolean allEqual = verifyAllEqualListElements.verifyAllEqualUsingApacheCommon(allEqualList);
+
+        assertTrue(allEqual);
+    }
+}