[BAEL-6339] custom iterator with testcases (#14038)

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

core-java-modules/core-java-collections-5/pom.xml

@@ -1,10 +1,22 @@
 <?xml version="1.0" encoding="UTF-8"?>
-<project xmlns="http://maven.apache.org/POM/4.0.0"
+<project xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+         xmlns="http://maven.apache.org/POM/4.0.0"
-    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
     <modelVersion>4.0.0</modelVersion>
     <artifactId>core-java-collections-5</artifactId>
     <name>core-java-collections-5</name>
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <configuration>
+                    <source>9</source>
+                    <target>9</target>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
     <packaging>jar</packaging>
 
     <parent>
@@ -54,5 +66,5 @@
         <roaringbitmap.version>0.9.38</roaringbitmap.version>
         <jmh.version>1.36</jmh.version>
     </properties>
-    
+
 </project>

core-java-modules/core-java-collections-5/src/main/java/com/baeldung/customiterators/CustomMovieIterator.java

@@ -0,0 +1,39 @@
+package com.baeldung.customiterators;
+
+import java.util.Iterator;
+import java.util.List;
+import java.util.NoSuchElementException;
+
+public class CustomMovieIterator implements Iterator<Movie> {
+    private int currentIndex;
+    private final List<Movie> list;
+
+    public CustomMovieIterator(List<Movie> list) {
+        this.list = list;
+        this.currentIndex = 0;
+    }
+
+    @Override
+    public boolean hasNext() {
+        while (currentIndex < list.size()) {
+            Movie currentMovie = list.get(currentIndex);
+            if (isMovieEligible(currentMovie)) {
+                return true;
+            }
+            currentIndex++;
+        }
+        return false;
+    }
+
+    @Override
+    public Movie next() {
+        if (!hasNext()) {
+            throw new NoSuchElementException();
+        }
+        return list.get(currentIndex++);
+    }
+
+    private boolean isMovieEligible(Movie movie) {
+        return movie.getRating() >= 8;
+    }
+}

core-java-modules/core-java-collections-5/src/main/java/com/baeldung/customiterators/Movie.java

@@ -0,0 +1,37 @@
+package com.baeldung.customiterators;
+
+public class Movie {
+    private String name;
+    private String director;
+    private float rating;
+
+    public Movie(String name, String director, float rating) {
+        this.name = name;
+        this.director = director;
+        this.rating = rating;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public String getDirector() {
+        return director;
+    }
+
+    public void setDirector(String director) {
+        this.director = director;
+    }
+
+    public float getRating() {
+        return rating;
+    }
+
+    public void setRating(float rating) {
+        this.rating = rating;
+    }
+}

core-java-modules/core-java-collections-5/src/main/java/com/baeldung/customiterators/MyList.java

@@ -0,0 +1,139 @@
+package com.baeldung.customiterators;
+
+import java.util.Collection;
+import java.util.Iterator;
+import java.util.List;
+import java.util.ListIterator;
+
+/**
+ * Please note that this class has been added for representation purposes of how a custom collection and its iterator would be.
+ * This does not have working code.
+ */
+public class MyList<E> implements List<E> {
+    @Override
+    public int size() {
+        return 0;
+    }
+
+    @Override
+    public boolean isEmpty() {
+        return false;
+    }
+
+    @Override
+    public boolean contains(Object o) {
+        return false;
+    }
+
+    @Override
+    public boolean add(E e) {
+        return false;
+    }
+
+    @Override
+    public boolean remove(Object o) {
+        return false;
+    }
+
+    @Override
+    public Iterator<E> iterator() {
+        return new MyListIterator();
+    }
+
+    private class MyListIterator implements Iterator<E> {
+        @Override
+        public boolean hasNext() {
+            return false;
+        }
+
+        @Override
+        public E next() {
+            return null;
+        }
+    }
+
+    @Override
+    public Object[] toArray() {
+        return new Object[0];
+    }
+
+    @Override
+    public <T> T[] toArray(T[] a) {
+        return null;
+    }
+
+    @Override
+    public boolean containsAll(Collection<?> c) {
+        return false;
+    }
+
+    @Override
+    public boolean addAll(Collection<? extends E> c) {
+        return false;
+    }
+
+    @Override
+    public boolean addAll(int index, Collection<? extends E> c) {
+        return false;
+    }
+
+    @Override
+    public boolean removeAll(Collection<?> c) {
+        return false;
+    }
+
+    @Override
+    public boolean retainAll(Collection<?> c) {
+        return false;
+    }
+
+    @Override
+    public void clear() {
+
+    }
+
+    @Override
+    public E get(int index) {
+        return null;
+    }
+
+    @Override
+    public E set(int index, E element) {
+        return null;
+    }
+
+    @Override
+    public void add(int index, E element) {
+
+    }
+
+    @Override
+    public E remove(int index) {
+        return null;
+    }
+
+    @Override
+    public int indexOf(Object o) {
+        return 0;
+    }
+
+    @Override
+    public int lastIndexOf(Object o) {
+        return 0;
+    }
+
+    @Override
+    public ListIterator<E> listIterator() {
+        return null;
+    }
+
+    @Override
+    public ListIterator<E> listIterator(int index) {
+        return null;
+    }
+
+    @Override
+    public List<E> subList(int fromIndex, int toIndex) {
+        return null;
+    }
+}

core-java-modules/core-java-collections-5/src/main/java/com/baeldung/customiterators/PalindromIterator.java

@@ -0,0 +1,44 @@
+package com.baeldung.customiterators;
+
+import java.util.Iterator;
+import java.util.List;
+import java.util.NoSuchElementException;
+
+public class PalindromIterator implements Iterator<String> {
+    private final List<String> list;
+    private int currentIndex;
+
+    public PalindromIterator(List<String> list) {
+        this.list = list;
+        this.currentIndex = 0;
+    }
+
+    @Override
+    public boolean hasNext() {
+        while (currentIndex < list.size()) {
+            String currString = list.get(currentIndex);
+            if (isPalindrome(currString)) {
+                return true;
+            }
+            currentIndex++;
+        }
+        return false;
+    }
+
+    @Override
+    public String next() {
+        if (!hasNext()) {
+            throw new NoSuchElementException();
+        }
+        return list.get(currentIndex++);
+    }
+
+    private boolean isPalindrome(String input) {
+        for (int i = 0; i < input.length() / 2; i++) {
+            if (input.charAt(i) != input.charAt(input.length() - i - 1)) {
+                return false;
+            }
+        }
+        return true;
+    }
+}

core-java-modules/core-java-collections-5/src/test/java/com/baeldung/customiterators/IteratorsUnitTest.java

@@ -0,0 +1,53 @@
+package com.baeldung.customiterators;
+
+import static org.junit.Assert.assertEquals;
+
+import java.util.Iterator;
+import java.util.List;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+public class IteratorsUnitTest {
+    @Test
+    public void givenListOfStrings_whenIteratedWithDefaultIterator() {
+        List<String> listOfStrings = List.of("hello", "world", "this", "is", "a", "test");
+        Iterator<String> iterator = listOfStrings.iterator();
+        Assert.assertTrue(iterator.hasNext());
+        assertEquals(iterator.next(), "hello");
+    }
+
+    @Test
+    public void givenListOfStrings_whenPalindromIterator_thenOnlyPalindromes() {
+        List<String> listOfStrings = List.of("oslo", "madam", "car", "deed", "wow", "test");
+        PalindromIterator palindromIterator = new PalindromIterator(listOfStrings);
+        int count = 0;
+        while (palindromIterator.hasNext()) {
+            palindromIterator.next();
+            count++;
+        }
+        assertEquals(count, 3);
+    }
+
+    @Test
+    public void givenMovieList_whenMovieIteratorUsed_thenOnlyHighRatedMovies() {
+        List<Movie> movies = getMovies();
+        CustomMovieIterator movieIterator = new CustomMovieIterator(movies);
+        int count = 0;
+        while (movieIterator.hasNext()) {
+            movieIterator.next();
+            count++;
+        }
+        assertEquals(4, movies.size());
+        assertEquals(2, count);
+    }
+
+    private List<Movie> getMovies() {
+        Movie movie1 = new Movie("The Dark Knight", "Nolan", 10);
+        Movie movie2 = new Movie("Avatar", "Cameron", 9);
+        Movie movie3 = new Movie("Tenet", "Nolan", 7);
+        Movie movie4 = new Movie("Extraction", "Hargrave", 5);
+        return List.of(movie1, movie2, movie3, movie4);
+    }
+
+}