src/me/ramswaroop/java8/FlatMapInStreams.java

@@ -0,0 +1,64 @@
+package me.ramswaroop.java8;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+
+/**
+ * @author ramswaroop
+ * @version 17/02/2017
+ */
+public class FlatMapInStreams {
+
+    public static long countTotalIngredientsInAllDishes(List<Dish> dishes) {
+        return dishes.stream().map(Dish::getIngredients).flatMap(List::stream).count();
+    }
+
+    public static void main(String[] a) {
+        List<String> ingredients = new ArrayList<>();
+        ingredients.add("rice");
+        ingredients.add("chicken");
+        ingredients.add("haldi");
+        List<Dish> dishes = Arrays.asList(
+                new Dish("biriyani", 600, ingredients),
+                new Dish("biriyani", 600, new ArrayList<>()));
+        // to show whether empty List is counted in flatMap
+        System.out.println(countTotalIngredientsInAllDishes(dishes)); 
+    }
+}
+
+class Dish {
+    private String name;
+    private int calories;
+    private List<String> ingredients;
+
+    public Dish(String name, int calories, List<String> ingredients) {
+        this.name = name;
+        this.calories = calories;
+        this.ingredients = ingredients;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public int getCalories() {
+        return calories;
+    }
+
+    public void setCalories(int calories) {
+        this.calories = calories;
+    }
+
+    public List<String> getIngredients() {
+        return ingredients;
+    }
+
+    public void setIngredients(List<String> ingredients) {
+        this.ingredients = ingredients;
+    }
+}