Ways to iterate over a list

jeetkunecoder · jzheaux · commit 5812866573fb · 2018-11-29T09:58:12.000-07:00
Issue: BAEL-2311
diff --git a/core-java-collections/src/main/java/com/baeldung/java/list/WaysToIterate.java b/core-java-collections/src/main/java/com/baeldung/java/list/WaysToIterate.java
@@ -0,0 +1,67 @@
+package com.baeldung.java.list;
+
+import java.util.Arrays;
+import java.util.Iterator;
+import java.util.List;
+import java.util.ListIterator;
+
+/**
+ *  Demonstrates the different ways to loop over
+ *  the elements of a list.
+ */
+public class WaysToIterate {
+
+    List<String> countries = Arrays.asList("Germany", "Panama", "Australia");
+
+    /**
+     * Iterate over a list using a basic for loop
+     */
+    public void iterateWithForLoop() {
+        for (int i = 0; i < countries.size(); i++) {
+            System.out.println(countries.get(i));
+        }
+    }
+
+    /**
+     * Iterate over a list using the enhanced for loop
+     */
+    public void iterateWithEnhancedForLoop() {
+        for (String country : countries) {
+            System.out.println(country);
+        }
+    }
+
+    /**
+     * Iterate over a list using an Iterator
+     */
+    public void iterateWithIterator() {
+        Iterator<String> countriesIterator = countries.iterator();
+        while(countriesIterator.hasNext()) {
+            System.out.println(countriesIterator.next());
+        }
+    }
+
+    /**
+     * Iterate over a list using a ListIterator
+     */
+    public void iterateWithListIterator() {
+        ListIterator<String> listIterator = countries.listIterator();
+        while(listIterator.hasNext()) {
+            System.out.println(listIterator.next());
+        }
+    }
+
+    /**
+     * Iterate over a list using the Iterable.forEach() method
+     */
+    public void iterateWithForEach() {
+        countries.forEach(System.out::println);
+    }
+
+    /**
+     * Iterate over a list using the Stream.forEach() method
+     */
+    public void iterateWithStreamForEach() {
+        countries.stream().forEach((c) -> System.out.println(c));
+    }
+}
diff --git a/core-java-collections/src/test/java/com/baeldung/java/list/WaysToIterateUnitTest.java b/core-java-collections/src/test/java/com/baeldung/java/list/WaysToIterateUnitTest.java
@@ -0,0 +1,71 @@
+package com.baeldung.java.list;
+
+import static org.junit.Assert.assertEquals;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Iterator;
+import java.util.List;
+import java.util.ListIterator;
+
+import org.junit.Test;
+
+public class WaysToIterateUnitTest {
+
+    List<String> globalCountries = new ArrayList<String>();
+    List<String> europeanCountries = Arrays.asList("Germany", "Panama", "Australia");
+
+    @Test
+    public void whenIteratingUsingForLoop_thenReturnThreeAsSizeOfList() {
+        for (int i = 0; i < europeanCountries.size(); i++) {
+            globalCountries.add(europeanCountries.get(i));
+        }
+        assertEquals(globalCountries.size(), 3);
+        globalCountries.clear();
+    }
+
+    @Test
+    public void whenIteratingUsingEnhancedForLoop_thenReturnThreeAsSizeOfList() {
+        for (String country : europeanCountries) {
+            globalCountries.add(country);
+        }
+        assertEquals(globalCountries.size(), 3);
+        globalCountries.clear();
+    }
+
+    @Test
+    public void whenIteratingUsingIterator_thenReturnThreeAsSizeOfList() {
+        Iterator<String> countriesIterator = europeanCountries.iterator();
+        while (countriesIterator.hasNext()) {
+            globalCountries.add(countriesIterator.next());
+        }
+
+        assertEquals(globalCountries.size(), 3);
+        globalCountries.clear();
+    }
+
+    @Test
+    public void whenIteratingUsingListIterator_thenReturnThreeAsSizeOfList() {
+        ListIterator<String> countriesIterator = europeanCountries.listIterator();
+        while (countriesIterator.hasNext()) {
+            globalCountries.add(countriesIterator.next());
+        }
+
+        assertEquals(globalCountries.size(), 3);
+        globalCountries.clear();
+    }
+
+    @Test
+    public void whenIteratingUsingForEach_thenReturnThreeAsSizeOfList() {
+        europeanCountries.forEach(country -> globalCountries.add(country));
+        assertEquals(globalCountries.size(), 3);
+        globalCountries.clear();
+    }
+
+    @Test
+    public void whenIteratingUsingStreamForEach_thenReturnThreeAsSizeOfList() {
+        europeanCountries.stream().forEach((country) -> globalCountries.add(country));
+        assertEquals(globalCountries.size(), 3);
+        globalCountries.clear();
+    }
+}
