Difference between Iterable and Iterator (#12079)
* Difference between Iterable and Iterator Add examples of the Iterable and the Iterator usage. * Minor changes Add UnitTests for Iterable examples * Fix iterable example Add Custom collection for the Iterable implementation example. * Fix iterable example Change the example for the Iterable interface implementation * Revert "Fix iterable example" This reverts commit 4015cbc038b1b657c54fa666193c0c7019a474ad. * Minor changes
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package com.baeldung.collections.iterable;
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class CustomIterableClient {
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public static void main(String[] args) {
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ShoppingCart<Product> shoppingCart = new ShoppingCart<>();
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shoppingCart.add(new Product("Tuna", 42));
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shoppingCart.add(new Product("Eggplant", 65));
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shoppingCart.add(new Product("Salad", 45));
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shoppingCart.add(new Product("Banana", 29));
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for (Product product : shoppingCart) {
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System.out.println(product.getName());
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}
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}
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}
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package com.baeldung.collections.iterable;
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import java.util.Iterator;
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import java.util.List;
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public class IterableExample {
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public void iterateUsingIterator(List<Integer> numbers) {
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Iterator<Integer> iterator = numbers.iterator();
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while (iterator.hasNext()) {
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System.out.println(iterator.next());
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}
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}
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public void iterateUsingEnhancedForLoop(List<Integer> numbers) {
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for (Integer number : numbers) {
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System.out.println(number);
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}
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}
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public void iterateUsingForEachLoop(List<Integer> numbers) {
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numbers.forEach(System.out::println);
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}
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public void removeElementsUsingIterator(List<Integer> numbers) {
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Iterator<Integer> iterator = numbers.iterator();
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while (iterator.hasNext()) {
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iterator.next();
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iterator.remove();
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}
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}
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}
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package com.baeldung.collections.iterable;
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class Product {
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private String name;
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private double price;
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public Product(String code, double price) {
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this.name = code;
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this.price = price;
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}
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public String getName() {
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return name;
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}
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public void setName(String name) {
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this.name = name;
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}
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public double getPrice() {
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return price;
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}
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public void setPrice(double price) {
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this.price = price;
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}
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}
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package com.baeldung.collections.iterable;
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import java.util.Arrays;
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import java.util.ConcurrentModificationException;
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import java.util.Iterator;
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import java.util.NoSuchElementException;
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public class ShoppingCart<E> implements Iterable<E> {
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private E[] elementData;
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private int size;
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public ShoppingCart() {
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this.elementData = (E[]) new Object[]{};
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}
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public void add(E element) {
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ensureCapacity(size + 1);
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elementData[size++] = element;
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}
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private void ensureCapacity(int minCapacity) {
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int oldCapacity = elementData.length;
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int newCapacity = oldCapacity + (oldCapacity >> 1);
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if (newCapacity - minCapacity < 0) {
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newCapacity = minCapacity;
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}
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elementData = Arrays.copyOf(elementData, newCapacity);
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}
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@Override
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public Iterator<E> iterator() {
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return new ShoppingCartIterator();
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}
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public class ShoppingCartIterator implements Iterator<E> {
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int cursor;
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int lastReturned = -1;
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public boolean hasNext() {
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return cursor != size;
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}
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public E next() {
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return getNextElement();
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}
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private E getNextElement() {
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int current = cursor;
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exist(current);
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E[] elements = ShoppingCart.this.elementData;
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validate(elements, current);
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cursor = current + 1;
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lastReturned = current;
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return elements[lastReturned];
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}
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private void exist(int current) {
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if (current >= size) {
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throw new NoSuchElementException();
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}
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}
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private void validate(E[] elements, int current) {
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if (current >= elements.length) {
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throw new ConcurrentModificationException();
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}
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}
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}
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}
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package com.baeldung.collections.iterator;
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import java.util.Iterator;
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class CustomIteratorClient {
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public static void main(String[] args) {
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Iterator<Integer> iterator = Numbers.iterator();
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while (iterator.hasNext()) {
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System.out.println(iterator.next());
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}
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}
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}
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package com.baeldung.collections.iterator;
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import java.util.Arrays;
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import java.util.Iterator;
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import java.util.List;
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import java.util.NoSuchElementException;
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class Numbers {
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private static final List<Integer> NUMBER_LIST = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
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private Numbers() {
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}
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public static Iterator<Integer> iterator() {
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return new PrimeIterator();
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}
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private static class PrimeIterator implements Iterator<Integer> {
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private int cursor;
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@Override
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public Integer next() {
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exist(cursor);
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return NUMBER_LIST.get(cursor++);
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}
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private void exist(int current) {
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if (current >= NUMBER_LIST.size()) {
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throw new NoSuchElementException();
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}
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}
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@Override
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public boolean hasNext() {
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if (cursor > NUMBER_LIST.size()) {
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return false;
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}
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for (int i = cursor; i < NUMBER_LIST.size(); i++) {
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if (isPrime(NUMBER_LIST.get(i))) {
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cursor = i;
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return true;
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}
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}
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return false;
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}
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private boolean isPrime(int number) {
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for (int i = 2; i <= number / 2; ++i) {
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if (number % i == 0) {
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return false;
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}
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}
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return true;
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}
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}
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}
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package com.baeldung.collections.iterable;
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import com.baeldung.collections.iterable.IterableExample;
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import org.junit.jupiter.api.Test;
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import java.util.ArrayList;
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import java.util.List;
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import static org.junit.jupiter.api.Assertions.assertEquals;
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class IterableUnitTest {
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private static List<Integer> getNumbers() {
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List<Integer> numbers = new ArrayList<>();
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numbers.add(10);
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numbers.add(20);
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numbers.add(30);
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numbers.add(40);
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return numbers;
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}
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@Test
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void givenNumbers_whenUsingIterator_thenCorrectSize() {
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List<Integer> numbers = getNumbers();
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IterableExample iterableExample = new IterableExample();
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iterableExample.iterateUsingIterator(numbers);
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assertEquals(4, numbers.size());
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}
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@Test
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void givenNumbers_whenRemoveElements_thenEmptyList() {
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List<Integer> numbers = getNumbers();
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IterableExample iterableExample = new IterableExample();
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iterableExample.removeElementsUsingIterator(numbers);
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assertEquals(0, numbers.size());
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}
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@Test
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void givenNumbers_whenIterateUsingEnhancedForLoop_thenCorrectSize() {
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List<Integer> numbers = getNumbers();
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IterableExample iterableExample = new IterableExample();
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iterableExample.iterateUsingEnhancedForLoop(numbers);
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assertEquals(4, numbers.size());
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}
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@Test
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void givenNumbers_whenIterateUsingForEachLoop_thenCorrectSize() {
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List<Integer> numbers = getNumbers();
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IterableExample iterableExample = new IterableExample();
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iterableExample.iterateUsingForEachLoop(numbers);
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assertEquals(4, numbers.size());
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}
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}
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