add examples of methods on Collection<>

src/section22/CollectionMethods.java

@@ -0,0 +1,74 @@
+package section22;
+
+import java.util.*;
+import java.util.stream.Stream;
+
+/**
+ * This example demonstrates key methods exposed by Collection<T> interface, which covers Lists and Sets.
+ */
+public class CollectionMethods {
+
+    public static void main(String[] argv) {
+        Collection<String> sample = new HashSet<>();
+
+        // add, addAll
+        sample.add("foo");
+        sample.addAll(Collections.singleton("bar"));
+        print(sample);
+
+        // clear, isEmpty
+        sample.clear();
+        System.out.println(sample.isEmpty());
+
+        // contains, containsAll
+        sample.add("foo");
+        sample.add("bar");
+        System.out.println(sample.contains("foo"));
+        System.out.println(sample.containsAll(Collections.singleton("baz")));
+
+        // iterator
+        Iterator<String> iter = sample.iterator();
+        while (iter.hasNext()) {
+            System.out.println(iter.next());
+        }
+
+        // remove, removeAll, removeIf
+        sample.add("fooooo");
+        sample.add("barrrr");
+        sample.add("");
+        sample.remove("");
+        print(sample);
+        sample.removeAll(Collections.singleton("foo"));
+        print(sample);
+        sample.removeIf(elem -> elem.length() > 3);
+        print(sample);
+
+        // retainAll
+        sample.retainAll(Collections.singleton("nothing"));
+        print(sample);
+
+        // size
+        System.out.println(sample.size());
+
+        // stream, parallelStream
+        sample.add("foo");
+        sample.add("bar");
+        Stream<String> stream = sample.stream();    // same for parallelStream, which could be parallel
+        stream.map(elem -> "hey " + elem).forEach(elem -> System.out.print(elem + "\t"));
+        System.out.println();
+
+        // toArray
+        Object[] array = sample.toArray();          // type erasure of generic type => we can only get Object[] :(
+        String[] stringArray = sample.toArray(new String[sample.size()]);   // better: feed in a typed array
+        System.out.println(Arrays.toString(stringArray));
+    }
+
+    public static void print(Collection<String> collection) {
+        System.out.print("|");
+        for (String elem : collection) {
+            System.out.print(elem + "\t");
+        }
+        System.out.println("|");
+    }
+
+}