BAEL-6838-index-of-set-element (#14747)

Co-authored-by: Bhaskar <bhaskar.dastidar@freshworks.com>

core-java-modules/core-java-collections-set-2/pom.xml

@@ -20,6 +20,12 @@
             <version>${junit-platform.version}</version>
             <scope>test</scope>
         </dependency>
+        <dependency>
+            <groupId>org.apache.commons</groupId>
+            <artifactId>commons-collections4</artifactId>
+            <version>4.4</version>
+        </dependency>
+
         <dependency>
             <groupId>org.testng</groupId>
             <artifactId>testng</artifactId>

core-java-modules/core-java-collections-set-2/src/main/java/com/baeldung/indexawareset/IndexOfElementsInSet.java

@@ -0,0 +1,13 @@
+package com.baeldung.indexawareset;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Set;
+
+public class IndexOfElementsInSet<E> {
+    public int getIndexOf(Set<E> set, E element) {
+        List<E> arrayList = new ArrayList<>();
+        arrayList.addAll(set);
+        return arrayList.indexOf(element);
+    }
+}

core-java-modules/core-java-collections-set-2/src/main/java/com/baeldung/indexawareset/InsertionIndexAwareSet.java

@@ -0,0 +1,20 @@
+package com.baeldung.indexawareset;
+
+import java.util.LinkedHashSet;
+
+public class InsertionIndexAwareSet<E> extends LinkedHashSet<E> {
+    public InsertionIndexAwareSet() {
+        super();
+    }
+
+    public int getIndexOf(E element) {
+        int index = 0;
+        for (E current : this) {
+            if (current.equals(element)) {
+                return index;
+            }
+            index++;
+        }
+        return -1;
+    }
+}

core-java-modules/core-java-collections-set-2/src/test/java/com/baeldung/indexawareset/IndexOfSetElementsUsingListUnitTest.java

@@ -0,0 +1,93 @@
+package com.baeldung.indexawareset;
+
+import java.util.HashSet;
+import java.util.LinkedHashSet;
+import java.util.Set;
+import java.util.TreeSet;
+
+import org.apache.commons.collections4.set.ListOrderedSet;
+import org.junit.Assert;
+import org.junit.Test;
+
+public class IndexOfSetElementsUsingListUnitTest {
+    @Test
+    public void givenHashSet_whenIndexOfElement_thenGivesIndex() {
+        Set<Integer> set = new HashSet<>();
+        set.add(100);
+        set.add(20);
+        set.add(300);
+        set.add(0);
+        set.add(-1);
+        set.add(300);
+
+        IndexOfElementsInSet<Integer> integerIndexOfElementsInSet = new IndexOfElementsInSet<>();
+        int index100 = integerIndexOfElementsInSet.getIndexOf(set, 100);
+        Assert.assertEquals(index100, integerIndexOfElementsInSet.getIndexOf(set, 100));
+        Assert.assertEquals(-1, integerIndexOfElementsInSet.getIndexOf(set, 12));
+    }
+
+    @Test
+    public void givenLinkedHashSet_whenIndexOfElement_thenGivesIndex() {
+        Set<Integer> set = new LinkedHashSet<>();
+        set.add(100);
+        set.add(20);
+        set.add(300);
+        set.add(0);
+        set.add(-1);
+        set.add(300);
+
+        IndexOfElementsInSet<Integer> integerIndexOfElementsInSet = new IndexOfElementsInSet<>();
+        Assert.assertEquals(0, integerIndexOfElementsInSet.getIndexOf(set, 100));
+    }
+
+    @Test
+    public void givenTreeSet_whenIndexOfElement_thenGivesIndex() {
+        Set<Integer> set = new TreeSet<>();
+        set.add(100);
+        set.add(20);
+        set.add(300);
+        set.add(0);
+        set.add(-1);
+        set.add(300);
+
+        IndexOfElementsInSet<Integer> integerIndexOfElementsInSet = new IndexOfElementsInSet<>();
+        Assert.assertEquals(0, integerIndexOfElementsInSet.getIndexOf(set, -1));
+        Assert.assertEquals(3, integerIndexOfElementsInSet.getIndexOf(set, 100));
+    }
+
+    @Test
+    public void givenIndexAwareSet_whenIndexOfElement_thenGivesIndex() {
+        InsertionIndexAwareSet<Integer> set = new InsertionIndexAwareSet<>();
+        set.add(100);
+        set.add(20);
+        set.add(300);
+        Assert.assertEquals(0, set.getIndexOf(100));
+        Assert.assertEquals(2, set.getIndexOf(300));
+        Assert.assertEquals(-1, set.getIndexOf(0));
+    }
+
+    @Test
+    public void givenIndexAwareSetWithStrings_whenIndexOfElement_thenGivesIndex() {
+        InsertionIndexAwareSet<String> set = new InsertionIndexAwareSet<>();
+        set.add("Go");
+        set.add("Java");
+        set.add("Scala");
+        set.add("Python");
+        Assert.assertEquals(0, set.getIndexOf("Go"));
+        Assert.assertEquals(2, set.getIndexOf("Scala"));
+        Assert.assertEquals(-1, set.getIndexOf("C++"));
+    }
+
+    @Test
+    public void givenListOrderedSet_whenIndexOfElement_thenGivesIndex() {
+        ListOrderedSet<Integer> set = new ListOrderedSet<>();
+        set.add(12);
+        set.add(0);
+        set.add(-1);
+        set.add(50);
+
+        Assert.assertEquals(0, set.indexOf(12));
+        Assert.assertEquals(2, set.indexOf(-1));
+        Assert.assertEquals(-1, set.indexOf(100));
+    }
+}