BAEL-7499: Check if an element is present in a Set in Java (#16065)

core-java-modules/core-java-collections-set-2/src/test/java/com/baeldung/checkifpresentinset/CheckIfPresentInSetUnitTest.java

@@ -0,0 +1,71 @@
+package com.baeldung.checkifpresentinset;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.Set;
+
+import org.apache.commons.collections4.CollectionUtils;
+import org.apache.commons.collections4.SetUtils;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
+class CheckIfPresentInSetUnitTest {
+
+    private static final Set<String> CITIES = new HashSet<>();
+
+    @BeforeAll
+    static void setup() {
+        CITIES.add("Paris");
+        CITIES.add("London");
+        CITIES.add("Tokyo");
+        CITIES.add("Tamassint");
+        CITIES.add("New york");
+    }
+
+    @Test
+    void givenASet_whenUsingStreamAnyMatchMethod_thenCheck() {
+        boolean isPresent = CITIES.stream()
+            .anyMatch(city -> city.equals("London"));
+
+        assertThat(isPresent).isTrue();
+    }
+
+    @Test
+    void givenASet_whenUsingStreamFilterMethod_thenCheck() {
+        long resultCount = CITIES.stream()
+            .filter(city -> city.equals("Tamassint"))
+            .count();
+
+        assertThat(resultCount).isPositive();
+    }
+
+    @Test
+    void givenASet_whenUsingContainsMethod_thenCheck() {
+        assertThat(CITIES.contains("London")).isTrue();
+        assertThat(CITIES.contains("Madrid")).isFalse();
+    }
+
+    @Test
+    void givenASet_whenUsingCollectionsDisjointMethod_thenCheck() {
+        boolean isPresent = !Collections.disjoint(CITIES, Collections.singleton("Paris"));
+
+        assertThat(isPresent).isTrue();
+    }
+
+    @Test
+    void givenASet_whenUsingCollectionUtilsContainsAnyMethod_thenCheck() {
+        boolean isPresent = CollectionUtils.containsAny(CITIES, Collections.singleton("Paris"));
+
+        assertThat(isPresent).isTrue();
+    }
+
+    @Test
+    void givenASet_whenUsingSetUtilsIntersectionMethod_thenCheck() {
+        Set<String> result = SetUtils.intersection(CITIES, Collections.singleton("Tamassint"));
+
+        assertThat(result).isNotEmpty();
+    }
+
+}