groupingBy() - with minBy, maxBy and collectingThen

spdpiyush · spdpiyush · commit 39d02236763c · 2025-03-07T17:01:06.000+05:30
diff --git a/Modern-Java-Examples/src/com/learn/streams_terminal/StreamsMinMaxCollectingThenExample.java b/Modern-Java-Examples/src/com/learn/streams_terminal/StreamsMinMaxCollectingThenExample.java
@@ -0,0 +1,71 @@
+package com.learn.streams_terminal;
+
+import com.learn.data.Student;
+import com.learn.data.StudentDataBase;
+
+import java.util.Comparator;
+import java.util.Map;
+import java.util.Optional;
+
+import static java.util.stream.Collectors.*;
+
+public class StreamsMinMaxCollectingThenExample {
+
+    public static void main(String[] args) {
+
+        System.out.println("Max Student with Optional" + optionalStudentWithMaximumGpa());
+        System.out.println("Max Student without Optional" + studentWithMaximumGpa());
+
+        System.out.println("Student with Least GPA in each Grade : " + studentWithMinimumGpa());
+
+    }
+
+    /**
+     * <p>
+     *     Calculate top Gpa Student in each Grade.
+     *     Here value is wrapped inside the Optional,
+     *     but we can avoid this by using CollectingAndThen
+     * </p>
+     */
+    public static Map<Integer, Optional<Student>> optionalStudentWithMaximumGpa() {
+        return StudentDataBase.getAllStudents()
+                .stream()
+                .collect(groupingBy(Student::getGradeLevel,
+                                maxBy(Comparator.comparing(Student::getGpa))));
+    }
+
+    /**
+     * <p>
+     *    collectingAndThen() : is going to get the Student if available and then assign that as an value.
+     * </p>
+     * @return
+     */
+    public static Map<Integer, Student> studentWithMaximumGpa() {
+        return StudentDataBase.getAllStudents()
+                .stream()
+                .collect(groupingBy(Student::getGradeLevel,
+                        collectingAndThen(maxBy(Comparator.comparing(Student::getGpa)),
+                                Optional::get)
+                        )
+                );
+    }
+
+
+    /**
+     * <p>
+     *     Calculate Least Gpa Student in each Grade.
+     * </p>
+     * @return
+     */
+    public static Map<Integer, Student> studentWithMinimumGpa() {
+        return StudentDataBase.getAllStudents()
+                .stream()
+                .collect(
+                        groupingBy(Student::getGradeLevel,
+                        collectingAndThen(
+                                minBy(Comparator.comparing(Student::getGpa)),
+                                Optional::get)
+                        )
+                );
+    }
+}
diff --git a/README.md b/README.md
@@ -49,6 +49,7 @@ This repository contains the basic &amp; advance level examples related to Java
     * [ minBy() and maxBy()](Modern-Java-Examples/src/com/learn/streams_terminal/StreamsMinByMaxByExample.java)
     * [ summingInt() and averagingInt()](Modern-Java-Examples/src/com/learn/streams_terminal/StreamsSumAvgExample.java)
     * [ groupingBy()](Modern-Java-Examples/src/com/learn/streams_terminal/StreamsGroupingByExample.java)
+    * [ groupingBy() - with maxBy(), minBy() and collectingThen()](Modern-Java-Examples/src/com/learn/streams_terminal/StreamsMinMaxCollectingThenExample.java)
 
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