Optional: filter(), map() and flatMap()

spdpiyush · spdpiyush · commit 70000fd91c07 · 2025-03-12T17:23:31.000+05:30
diff --git a/Modern-Java-Examples/src/com/learn/data/Bike.java b/Modern-Java-Examples/src/com/learn/data/Bike.java
@@ -0,0 +1,31 @@
+package com.learn.data;
+
+public class Bike {
+
+    private String name;
+    private String model;
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public String getModel() {
+        return model;
+    }
+
+    public void setModel(String model) {
+        this.model = model;
+    }
+
+    @Override
+    public String toString() {
+        return "Bike{" +
+                "name='" + name + '\'' +
+                ", model='" + model + '\'' +
+                '}';
+    }
+}
diff --git a/Modern-Java-Examples/src/com/learn/data/Student.java b/Modern-Java-Examples/src/com/learn/data/Student.java
@@ -1,6 +1,7 @@
 package com.learn.data;
 
 import java.util.List;
+import java.util.Optional;
 
 public class Student {
 
@@ -10,6 +11,7 @@ public class Student {
     private double gpa;
     private List<String> activities;
     private int noteBooks;
+    private Optional<Bike> bike = Optional.empty();
 
     public Student(String name, int gradeLevel, String gender, double gpa, List<String> activities) {
         this.name = name;
@@ -84,14 +86,24 @@ public void setNoteBooks(int noteBooks) {
         this.noteBooks = noteBooks;
     }
 
+    public Optional<Bike> getBike() {
+        return bike;
+    }
+
+    public void setBike(Optional<Bike> bike) {
+        this.bike = bike;
+    }
+
     @Override
     public String toString() {
         return "Student{" +
                 "name='" + name + '\'' +
-                ", gradeLevel='" + gradeLevel + '\'' +
+                ", gradeLevel=" + gradeLevel +
                 ", gender='" + gender + '\'' +
                 ", gpa=" + gpa +
                 ", activities=" + activities +
+                ", noteBooks=" + noteBooks +
+                ", bike=" + bike +
                 '}';
     }
 }
diff --git a/Modern-Java-Examples/src/com/learn/data/StudentDataBase.java b/Modern-Java-Examples/src/com/learn/data/StudentDataBase.java
@@ -3,6 +3,7 @@
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
+import java.util.Optional;
 import java.util.function.Supplier;
 
 public class StudentDataBase {
@@ -11,7 +12,14 @@ public class StudentDataBase {
     /**
      * Utility Method to return 1 Student.
      */
-    public static Supplier<Student> studentSupplier = () -> new Student("Adam", 2, "male", 4.5, Arrays.asList("swimming", "basketball"));
+    public static Supplier<Student> studentSupplier = () -> {
+        Bike bike = new Bike();
+        bike.setName("Honda");
+        bike.setModel("X1");
+        Student student = new Student("Adam", 2, "male", 4.5, Arrays.asList("swimming", "basketball"));
+        student.setBike(Optional.ofNullable(bike));
+        return student;
+    };
 
     /**
      * Dummy Student Data
diff --git a/Modern-Java-Examples/src/com/learn/optional/OptionalMapFlatMapExample.java b/Modern-Java-Examples/src/com/learn/optional/OptionalMapFlatMapExample.java
@@ -0,0 +1,72 @@
+package com.learn.optional;
+
+import com.learn.data.Bike;
+import com.learn.data.Student;
+import com.learn.data.StudentDataBase;
+
+import java.util.Optional;
+
+public class OptionalMapFlatMapExample {
+
+    public static void main(String[] args) {
+
+        optionalFilterExample();
+        optionalMapExample();
+        optionalFlatMapExample();
+    }
+
+    /**
+     * If a value is present, and the value matches the given predicate,
+     * returns an {@code Optional} describing the value, otherwise returns an
+     * empty {@code Optional}.
+     * filter
+     */
+    public static void optionalFilterExample() {
+
+        Optional<Student> studentOptional = Optional.ofNullable(StudentDataBase.studentSupplier.get());
+        // apply filter before we get actual value.
+        studentOptional
+                .filter(student -> student.getGpa() >= 3.9)
+                .ifPresent(System.out::println);
+
+    }
+
+    /**
+     * If a value is present, returns an {@code Optional} describing (as if by
+     * the result of applying the given mapping function to
+     * the value, otherwise returns an empty {@code Optional}.
+     *
+     * If the mapping function returns a {@code null} result then this method
+     * returns an empty {@code Optional}.
+     */
+    public static void optionalMapExample() {
+
+        Optional<Student> studentOptional = Optional.ofNullable(StudentDataBase.studentSupplier.get());
+        if (studentOptional.isPresent()) {
+            Optional<String> stringOptional = studentOptional
+                    .filter(student -> student.getGpa() >= 3.9)
+                    .map(Student::getName);
+            System.out.println(stringOptional);
+
+        }
+    }
+
+    /**
+     * To get Optional Object inside an Optional object, the only way to get it
+     * is by using flatMap()
+     *
+     * In Optional Context, flatMap() is used to get the actual value of the Optional object inside
+     * another Optional object.
+     */
+    public static void optionalFlatMapExample() {
+
+        Optional<Student> studentOptional = Optional.ofNullable(StudentDataBase.studentSupplier.get());
+
+        Optional<String> stringOptional = studentOptional
+                .filter(student -> student.getGpa() >= 3.9) // Optional<Student <Optional<Bike> >
+                .flatMap(Student::getBike) // Optional<Bike>
+                .map(Bike::getName);
+
+        System.out.println(stringOptional);
+    }
+}
diff --git a/README.md b/README.md
@@ -61,6 +61,7 @@ This repository contains the basic &amp; advance level examples related to Java
     * [ofNullable(), of() and empty()](Modern-Java-Examples/src/com/learn/optional/OptionalOfEmptyNullableExample.java)
     * [orElse(), orElseGet() and orElseThrow()](Modern-Java-Examples/src/com/learn/optional/OptionalOrElseExample.java)
     * [ifPresent() and isPresent()](Modern-Java-Examples/src/com/learn/optional/OptionalPresentExample.java)
+    * [filter(), map() and flatMap()](Modern-Java-Examples/src/com/learn/optional/OptionalMapFlatMapExample.java)
 
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