Fix iterable example

Change the example for the Iterable interface implementation

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

@@ -1,72 +0,0 @@
-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

@@ -4,13 +4,13 @@ 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));
+        ShoppingCart shoppingCart = new ShoppingCart();
+        shoppingCart.add(new Product("Tuna", 42));
+        shoppingCart.add(new Product("Eggplant", 65));
+        shoppingCart.add(new Product("Salad", 45));
+        shoppingCart.add(new Product("Banana", 29));
 
-        for (Product product : products) {
+        for (Product product : shoppingCart) {
             System.out.println(product.getName());
         }
     }

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

@@ -0,0 +1,36 @@
+package com.baeldung.collections.iterable;
+
+class Element {
+
+    private Element prev;
+    private Element next;
+    private Product product;
+
+    public Element(Product product) {
+        this.product = product;
+    }
+
+    public Element getPrev() {
+        return prev;
+    }
+
+    public void setPrev(Element prev) {
+        this.prev = prev;
+    }
+
+    public Element getNext() {
+        return next;
+    }
+
+    public void setNext(Element next) {
+        this.next = next;
+    }
+
+    public Product getProduct() {
+        return product;
+    }
+
+    public void setProduct(Product product) {
+        this.product = product;
+    }
+}

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

@@ -0,0 +1,71 @@
+package com.baeldung.collections.iterable;
+
+import java.util.Iterator;
+import java.util.NoSuchElementException;
+
+class ShoppingCart implements Iterable<Product> {
+
+    private Element firstElement;
+    private Element lastElement;
+
+    public void add(Product product) {
+        Element newElement = new Element(product);
+        connectElements(newElement);
+    }
+
+    private void connectElements(Element newElement) {
+        if (isEmpty()) {
+            addFirstElement(newElement);
+            return;
+        }
+
+        addLastElement(newElement);
+    }
+
+    private boolean isEmpty() {
+        return firstElement == null;
+    }
+
+    private void addFirstElement(Element newElement) {
+        firstElement = newElement;
+        lastElement = newElement;
+    }
+
+    private void addLastElement(Element newElement) {
+        newElement.setPrev(lastElement);
+        lastElement.setNext(newElement);
+        lastElement = newElement;
+    }
+
+    @Override
+    public Iterator<Product> iterator() {
+        return new ShoppingCartIterator();
+    }
+
+    class ShoppingCartIterator implements Iterator<Product> {
+        private Element currentElement;
+
+        public ShoppingCartIterator() {
+            currentElement = ShoppingCart.this.firstElement;
+        }
+
+        @Override
+        public boolean hasNext() {
+            return currentElement != null;
+        }
+
+        @Override
+        public Product next() {
+            if (!hasNext()) {
+                throw new NoSuchElementException();
+            }
+            return getNext();
+        }
+
+        private Product getNext() {
+            Element element = currentElement;
+            currentElement = currentElement.getNext();
+            return element.getProduct();
+        }
+    }
+}