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basahota · web-flow · commit 0587c1dc1313 · 2021-01-17T17:01:54.000+05:30
diff --git a/mapVsflatMap/Customer.java b/mapVsflatMap/Customer.java
@@ -0,0 +1,53 @@
+package com.javatechie;
+
+import java.util.List;
+
+public class Customer {
+
+    private int id;
+    private String name;
+    private String email;
+    private List<String> phoneNumbers;
+
+    public Customer() {
+    }
+
+    public Customer(int id, String name, String email, List<String> phoneNumbers) {
+        this.id = id;
+        this.name = name;
+        this.email = email;
+        this.phoneNumbers = phoneNumbers;
+    }
+
+    public int getId() {
+        return id;
+    }
+
+    public void setId(int id) {
+        this.id = id;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public String getEmail() {
+        return email;
+    }
+
+    public void setEmail(String email) {
+        this.email = email;
+    }
+
+    public List<String> getPhoneNumbers() {
+        return phoneNumbers;
+    }
+
+    public void setPhoneNumbers(List<String> phoneNumbers) {
+        this.phoneNumbers = phoneNumbers;
+    }
+}
diff --git a/mapVsflatMap/EkartDataBase.java b/mapVsflatMap/EkartDataBase.java
@@ -0,0 +1,21 @@
+package com.javatechie;
+
+import java.util.Arrays;
+import java.util.List;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+public class EkartDataBase {
+
+
+    public static List<Customer> getAll() {
+        return Stream.of(
+                new Customer(101, "john", "john@gmail.com", Arrays.asList("397937955", "21654725")),
+                new Customer(102, "smith", "smith@gmail.com", Arrays.asList("89563865", "2487238947")),
+                new Customer(103, "peter", "peter@gmail.com", Arrays.asList("38946328654", "3286487236")),
+                new Customer(104, "kely", "kely@gmail.com", Arrays.asList("389246829364", "948609467"))
+        ).collect(Collectors.toList());
+    }
+
+
+}
diff --git a/mapVsflatMap/MapVsFlatMap.java b/mapVsflatMap/MapVsFlatMap.java
@@ -0,0 +1,34 @@
+package com.javatechie;
+
+import java.util.List;
+import java.util.stream.Collectors;
+
+public class MapVsFlatMap {
+    public static void main(String[] args) {
+
+        List<Customer> customers = EkartDataBase.getAll();
+
+        //List<Customer>  convert List<String> -> Data Transformation
+        //mapping : customer -> customer.getEmail()
+        //customer -> customer.getEmail()  one to one mapping
+        List<String> emails = customers.stream()
+                .map(customer -> customer.getEmail())
+                .collect(Collectors.toList());
+        System.out.println(emails);
+
+//customer -> customer.getPhoneNumbers()  ->> one to many mapping
+        //customer -> customer.getPhoneNumbers()  ->> one to many mapping
+        List<List<String>> phoneNumbers = customers.
+                stream().map(customer -> customer.getPhoneNumbers())
+                .collect(Collectors.toList());
+        System.out.println(phoneNumbers);
+
+        //List<Customer>  convert List<String> -> Data Transformation
+        //mapping : customer -> phone Numbers
+        //customer -> customer.getPhoneNumbers()  ->> one to many mapping
+        List<String> phones = customers.stream()
+                .flatMap(customer -> customer.getPhoneNumbers().stream())
+                .collect(Collectors.toList());
+        System.out.println(phones);
+    }
+}
diff --git a/mapVsflatMap/readme.md b/mapVsflatMap/readme.md
@@ -0,0 +1,11 @@
+Differences between Java 8 Map() Vs flatMap() :
+
+map() | flatMap() | 
+--- | --- |  
+It processes stream of values. | It processes stream of stream of values. 
+It does only mapping. | It performs mapping as well as flattening.
+It’s mapper function produces single value for each input value. | It’s mapper function produces multiple values for each input value. 
+It is a One-To-One mapping. | It is a One-To-Many mapping. 
+Data Transformation : From Stream<T> to Stream<R> | Data Transformation : From Stream<Stream<T> to Stream<R> 
+Use this method when the mapper function is producing a single value for each input value. | Use this method when the mapper function is producing multiple values for each input value. 
+
