Adding Streams Example

Author: spdpiyush

Modern-Java-Examples/src/com/learn/streams/StreamsExample.java

@@ -0,0 +1,56 @@
+package com.learn.streams;
+
+import com.learn.data.Student;
+import com.learn.data.StudentDataBase;
+
+import java.util.List;
+import java.util.Map;
+import java.util.function.Predicate;
+import java.util.stream.Collectors;
+
+public class StreamsExample {
+
+    public static void main(String[] args) {
+
+        // we want student name and their activities in a Map
+        Map<String, List<String>> studentActivitiesMap = StudentDataBase.getAllStudents()
+                .stream()
+                .collect(Collectors.toMap(Student::getName, Student::getActivities));
+
+        /**
+         * collect method starts the whole process.
+         */
+        System.out.println(studentActivitiesMap);
+
+        // with filter
+        Map<String, List<String>> studentActivitiesMapWithFilter = StudentDataBase.getAllStudents()
+                .stream()
+                .filter(student -> student.getGradeLevel() >= 3)
+                .collect(Collectors.toMap(Student::getName, Student::getActivities));
+        System.out.println(studentActivitiesMapWithFilter);
+
+        Predicate<Student> predicate1 = student -> student.getGradeLevel() >= 3;
+        Predicate<Student> predicate2 = student -> student.getGpa() >= 3.9;
+        Map<String, List<String>> studentActivitiesMapWithTwoFilter = StudentDataBase.getAllStudents()
+                .stream()
+                .filter(predicate1)
+                .filter(predicate2)
+                .collect(Collectors.toMap(Student::getName, Student::getActivities));
+        System.out.println(studentActivitiesMapWithTwoFilter);
+
+        Predicate<Student> predicate4 = (student -> {
+            System.out.println(student);
+            return student.getGradeLevel() >= 3;
+        });
+
+        /**
+         * collect method starts the whole process.
+         * if we don't have collect then this won't even start.
+         * Streams are Lazy.
+         * i.e. No Intermediate Operations will be invoked until the terminal operation is invoked.
+         */
+        StudentDataBase.getAllStudents()
+                .stream()
+                .filter(predicate4);
+    }
+}

README.md

@@ -21,6 +21,8 @@ This repository contains the basic & advance level examples related to Java
     * [Refactoring Method Reference](Modern-Java-Examples/src/com/learn/methodreference/RefactorMethodReferenceExample.java)
   * [Constructor Reference](Modern-Java-Examples/src/com/learn/constructorreference/ConstructorReferenceExample.java)
   * [Lambdas and Local Variables](Modern-Java-Examples/src/com/learn/lambdas/LambdaVariable1.java)
+  * [Streams](Modern-Java-Examples/src/com/learn/streams)
+    * [Stream Example](Modern-Java-Examples/src/com/learn/streams/StreamsExample.java)