Fix iterable example

Add Custom collection for the Iterable implementation example.

core-java-modules/core-java-collections-2/src/main/java/com/baeldung/collections/iterable/CustomCollection.java

@@ -0,0 +1,72 @@
+package com.baeldung.collections.iterable;
+
+import java.util.Arrays;
+import java.util.ConcurrentModificationException;
+import java.util.Iterator;
+import java.util.NoSuchElementException;
+
+public class CustomCollection<E> implements Iterable<E> {
+
+    private E[] elementData;
+    private int size;
+
+    public CustomCollection() {
+        this.elementData = (E[]) new Object[] {};
+    }
+
+    public void add(E element) {
+        ensureCapacity(size + 1);
+        elementData[size++] = element;
+    }
+
+    private void ensureCapacity(int minCapacity) {
+        int oldCapacity = elementData.length;
+        int newCapacity = oldCapacity + (oldCapacity >> 1);
+        if (newCapacity - minCapacity < 0) {
+            newCapacity = minCapacity;
+        }
+        elementData = Arrays.copyOf(elementData, newCapacity);
+    }
+
+    @Override
+    public Iterator<E> iterator() {
+        return new CollectionIterator();
+    }
+
+    public class CollectionIterator implements Iterator<E> {
+        int cursor;
+        int lastReturned = -1;
+
+        public boolean hasNext() {
+            return cursor != size;
+        }
+
+        public E next() {
+            return getNextElement();
+        }
+
+        private E getNextElement() {
+            int current = cursor;
+            exist(current);
+
+            E[] elements = CustomCollection.this.elementData;
+            validate(elements, current);
+
+            cursor = current + 1;
+            lastReturned = current;
+            return elements[lastReturned];
+        }
+
+        private void exist(int current) {
+            if (current >= size) {
+                throw new NoSuchElementException();
+            }
+        }
+
+        private void validate(E[] elements, int current) {
+            if (current >= elements.length) {
+                throw new ConcurrentModificationException();
+            }
+        }
+    }
+}

core-java-modules/core-java-collections-2/src/main/java/com/baeldung/collections/iterable/CustomIterableClient.java

@@ -0,0 +1,17 @@
+package com.baeldung.collections.iterable;
+
+class CustomIterableClient {
+
+    public static void main(String[] args) {
+
+        CustomCollection<Product> products = new CustomCollection<>();
+        products.add(new Product("Tuna", 42));
+        products.add(new Product("Eggplant", 65));
+        products.add(new Product("Salad", 45));
+        products.add(new Product("Banana", 29));
+
+        for (Product product : products) {
+            System.out.println(product.getName());
+        }
+    }
+}

core-java-modules/core-java-collections-2/src/main/java/com/baeldung/collections/iterable/ProductIterable.java

@@ -1,18 +0,0 @@
-package com.baeldung.collections.iterable;
-
-import java.util.Iterator;
-import java.util.List;
-
-class ProductIterable implements Iterable<Product> {
-
-    List<Product> productList;
-
-    public ProductIterable(List<Product> productList) {
-        this.productList = productList;
-    }
-
-    @Override
-    public Iterator<Product> iterator() {
-        return productList.iterator();
-    }
-}

core-java-modules/core-java-collections-2/src/main/java/com/baeldung/collections/iterable/ProductIterableClient.java

@@ -1,17 +0,0 @@
-package com.baeldung.collections.iterable;
-
-import java.util.Arrays;
-import java.util.List;
-
-class ProductIterableClient {
-
-    public static void main(String[] args) {
-        List<Product> products = Arrays.asList(new Product("Salad", 45), new Product("Tuna", 42), new Product("Eggplant", 65), new Product("Bread", 22), new Product("Banana", 29));
-
-        ProductIterable iterable = new ProductIterable(products);
-
-        for (Product product : iterable) {
-            System.out.println(product.getName());
-        }
-    }
-}

core-java-modules/core-java-collections-2/src/main/java/com/baeldung/collections/iterator/CustomIterator.java

@@ -1,8 +0,0 @@
-package com.baeldung.collections.iterator;
-
-interface CustomIterator<T> {
-
-    boolean hasNext();
-
-    T next();
-}

core-java-modules/core-java-collections-2/src/main/java/com/baeldung/collections/iterator/CustomIteratorClient.java

@@ -1,9 +1,11 @@
 package com.baeldung.collections.iterator;
 
+import java.util.Iterator;
+
 class CustomIteratorClient {
 
     public static void main(String[] args) {
-        CustomIterator<Integer> iterator = Numbers.iterator();
+        Iterator<Integer> iterator = Numbers.iterator();
 
         while (iterator.hasNext()) {
             System.out.println(iterator.next());

core-java-modules/core-java-collections-2/src/main/java/com/baeldung/collections/iterator/Numbers.java

@@ -1,24 +1,54 @@
 package com.baeldung.collections.iterator;
 
 import java.util.Arrays;
+import java.util.Iterator;
 import java.util.List;
+import java.util.NoSuchElementException;
 
 class Numbers {
 
-    private static final List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
+    private static final List<Integer> NUMBER_LIST = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
 
     private Numbers() {
     }
 
-    public static CustomIterator<Integer> iterator() {
+    public static Iterator<Integer> iterator() {
         return new PrimeIterator();
     }
 
-    private static class PrimeIterator implements CustomIterator<Integer> {
+    private static class PrimeIterator implements Iterator<Integer> {
 
-        private int currentPosition;
+        private int cursor;
 
-        private static boolean isPrime(int number) {
+        @Override
+        public Integer next() {
+            exist(cursor);
+            return NUMBER_LIST.get(cursor++);
+        }
+
+        private void exist(int current) {
+            if (current >= NUMBER_LIST.size()) {
+                throw new NoSuchElementException();
+            }
+        }
+
+        @Override
+        public boolean hasNext() {
+            if (cursor > NUMBER_LIST.size()) {
+                return false;
+            }
+
+            for (int i = cursor; i < NUMBER_LIST.size(); i++) {
+                if (isPrime(NUMBER_LIST.get(i))) {
+                    cursor = i;
+                    return true;
+                }
+            }
+
+            return false;
+        }
+
+        private boolean isPrime(int number) {
             for (int i = 2; i <= number / 2; ++i) {
                 if (number % i == 0) {
                     return false;
@@ -26,26 +56,5 @@ class Numbers {
             }
             return true;
         }
-
-        @Override
-        public Integer next() {
-            return numbers.get(currentPosition++);
-        }
-
-        @Override
-        public boolean hasNext() {
-            if (currentPosition > numbers.size()) {
-                return false;
-            }
-
-            for (int i = currentPosition; i < numbers.size(); i++) {
-                if (isPrime(numbers.get(i))) {
-                    currentPosition = i;
-                    return true;
-                }
-            }
-
-            return false;
-        }
     }
 }

core-java-modules/core-java-collections-2/src/test/java/com/baeldung/collections/iterable/IterableUnitTest.java

@@ -51,4 +51,4 @@ class IterableUnitTest {
         iterableExample.iterateUsingForEachLoop(numbers);
         assertEquals(4, numbers.size());
     }
-}
+}