From fa471700258ecc5ec946b360751d86eb48ff913e Mon Sep 17 00:00:00 2001 From: apeterlic Date: Sun, 8 May 2022 08:38:49 +0200 Subject: [PATCH] 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 --- .../iterable/CustomIterableClient.java | 17 +++++ .../collections/iterable/IterableExample.java | 32 +++++++++ .../collections/iterable/Product.java | 28 ++++++++ .../collections/iterable/ShoppingCart.java | 72 +++++++++++++++++++ .../iterator/CustomIteratorClient.java | 14 ++++ .../collections/iterator/Numbers.java | 60 ++++++++++++++++ .../iterable/IterableUnitTest.java | 54 ++++++++++++++ 7 files changed, 277 insertions(+) create mode 100644 core-java-modules/core-java-collections-2/src/main/java/com/baeldung/collections/iterable/CustomIterableClient.java create mode 100644 core-java-modules/core-java-collections-2/src/main/java/com/baeldung/collections/iterable/IterableExample.java create mode 100644 core-java-modules/core-java-collections-2/src/main/java/com/baeldung/collections/iterable/Product.java create mode 100644 core-java-modules/core-java-collections-2/src/main/java/com/baeldung/collections/iterable/ShoppingCart.java create mode 100644 core-java-modules/core-java-collections-2/src/main/java/com/baeldung/collections/iterator/CustomIteratorClient.java create mode 100644 core-java-modules/core-java-collections-2/src/main/java/com/baeldung/collections/iterator/Numbers.java create mode 100644 core-java-modules/core-java-collections-2/src/test/java/com/baeldung/collections/iterable/IterableUnitTest.java diff --git a/core-java-modules/core-java-collections-2/src/main/java/com/baeldung/collections/iterable/CustomIterableClient.java b/core-java-modules/core-java-collections-2/src/main/java/com/baeldung/collections/iterable/CustomIterableClient.java new file mode 100644 index 0000000000..14f7b18014 --- /dev/null +++ b/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) { + + 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 : shoppingCart) { + System.out.println(product.getName()); + } + } +} diff --git a/core-java-modules/core-java-collections-2/src/main/java/com/baeldung/collections/iterable/IterableExample.java b/core-java-modules/core-java-collections-2/src/main/java/com/baeldung/collections/iterable/IterableExample.java new file mode 100644 index 0000000000..9110d6a15f --- /dev/null +++ b/core-java-modules/core-java-collections-2/src/main/java/com/baeldung/collections/iterable/IterableExample.java @@ -0,0 +1,32 @@ +package com.baeldung.collections.iterable; + +import java.util.Iterator; +import java.util.List; + +public class IterableExample { + + public void iterateUsingIterator(List numbers) { + Iterator iterator = numbers.iterator(); + while (iterator.hasNext()) { + System.out.println(iterator.next()); + } + } + + public void iterateUsingEnhancedForLoop(List numbers) { + for (Integer number : numbers) { + System.out.println(number); + } + } + + public void iterateUsingForEachLoop(List numbers) { + numbers.forEach(System.out::println); + } + + public void removeElementsUsingIterator(List numbers) { + Iterator iterator = numbers.iterator(); + while (iterator.hasNext()) { + iterator.next(); + iterator.remove(); + } + } +} diff --git a/core-java-modules/core-java-collections-2/src/main/java/com/baeldung/collections/iterable/Product.java b/core-java-modules/core-java-collections-2/src/main/java/com/baeldung/collections/iterable/Product.java new file mode 100644 index 0000000000..b29088f6f0 --- /dev/null +++ b/core-java-modules/core-java-collections-2/src/main/java/com/baeldung/collections/iterable/Product.java @@ -0,0 +1,28 @@ +package com.baeldung.collections.iterable; + +class Product { + + private String name; + private double price; + + public Product(String code, double price) { + this.name = code; + this.price = price; + } + + public String getName() { + return name; + } + + public void setName(String name) { + this.name = name; + } + + public double getPrice() { + return price; + } + + public void setPrice(double price) { + this.price = price; + } +} diff --git a/core-java-modules/core-java-collections-2/src/main/java/com/baeldung/collections/iterable/ShoppingCart.java b/core-java-modules/core-java-collections-2/src/main/java/com/baeldung/collections/iterable/ShoppingCart.java new file mode 100644 index 0000000000..f1b481da08 --- /dev/null +++ b/core-java-modules/core-java-collections-2/src/main/java/com/baeldung/collections/iterable/ShoppingCart.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 ShoppingCart implements Iterable { + + private E[] elementData; + private int size; + + public ShoppingCart() { + 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 iterator() { + return new ShoppingCartIterator(); + } + + public class ShoppingCartIterator implements Iterator { + 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 = ShoppingCart.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(); + } + } + } +} diff --git a/core-java-modules/core-java-collections-2/src/main/java/com/baeldung/collections/iterator/CustomIteratorClient.java b/core-java-modules/core-java-collections-2/src/main/java/com/baeldung/collections/iterator/CustomIteratorClient.java new file mode 100644 index 0000000000..30c8f57c0b --- /dev/null +++ b/core-java-modules/core-java-collections-2/src/main/java/com/baeldung/collections/iterator/CustomIteratorClient.java @@ -0,0 +1,14 @@ +package com.baeldung.collections.iterator; + +import java.util.Iterator; + +class CustomIteratorClient { + + public static void main(String[] args) { + Iterator iterator = Numbers.iterator(); + + while (iterator.hasNext()) { + System.out.println(iterator.next()); + } + } +} diff --git a/core-java-modules/core-java-collections-2/src/main/java/com/baeldung/collections/iterator/Numbers.java b/core-java-modules/core-java-collections-2/src/main/java/com/baeldung/collections/iterator/Numbers.java new file mode 100644 index 0000000000..23b3344c08 --- /dev/null +++ b/core-java-modules/core-java-collections-2/src/main/java/com/baeldung/collections/iterator/Numbers.java @@ -0,0 +1,60 @@ +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 NUMBER_LIST = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10); + + private Numbers() { + } + + public static Iterator iterator() { + return new PrimeIterator(); + } + + private static class PrimeIterator implements Iterator { + + private int cursor; + + @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; + } + } + return true; + } + } +} diff --git a/core-java-modules/core-java-collections-2/src/test/java/com/baeldung/collections/iterable/IterableUnitTest.java b/core-java-modules/core-java-collections-2/src/test/java/com/baeldung/collections/iterable/IterableUnitTest.java new file mode 100644 index 0000000000..745dcf52b7 --- /dev/null +++ b/core-java-modules/core-java-collections-2/src/test/java/com/baeldung/collections/iterable/IterableUnitTest.java @@ -0,0 +1,54 @@ +package com.baeldung.collections.iterable; + +import com.baeldung.collections.iterable.IterableExample; + +import org.junit.jupiter.api.Test; + +import java.util.ArrayList; +import java.util.List; + +import static org.junit.jupiter.api.Assertions.assertEquals; + +class IterableUnitTest { + + private static List getNumbers() { + List numbers = new ArrayList<>(); + numbers.add(10); + numbers.add(20); + numbers.add(30); + numbers.add(40); + return numbers; + } + + @Test + void givenNumbers_whenUsingIterator_thenCorrectSize() { + List numbers = getNumbers(); + IterableExample iterableExample = new IterableExample(); + iterableExample.iterateUsingIterator(numbers); + assertEquals(4, numbers.size()); + } + + @Test + void givenNumbers_whenRemoveElements_thenEmptyList() { + List numbers = getNumbers(); + IterableExample iterableExample = new IterableExample(); + iterableExample.removeElementsUsingIterator(numbers); + assertEquals(0, numbers.size()); + } + + @Test + void givenNumbers_whenIterateUsingEnhancedForLoop_thenCorrectSize() { + List numbers = getNumbers(); + IterableExample iterableExample = new IterableExample(); + iterableExample.iterateUsingEnhancedForLoop(numbers); + assertEquals(4, numbers.size()); + } + + @Test + void givenNumbers_whenIterateUsingForEachLoop_thenCorrectSize() { + List numbers = getNumbers(); + IterableExample iterableExample = new IterableExample(); + iterableExample.iterateUsingForEachLoop(numbers); + assertEquals(4, numbers.size()); + } +}