groupingBy() collector

spdpiyush · spdpiyush · commit 05df44068640 · 2025-03-06T14:51:25.000+05:30
diff --git a/Modern-Java-Examples/src/com/learn/streams_terminal/StreamsGroupingByExample.java b/Modern-Java-Examples/src/com/learn/streams_terminal/StreamsGroupingByExample.java
@@ -0,0 +1,57 @@
+package com.learn.streams_terminal;
+
+import com.learn.data.Student;
+import com.learn.data.StudentDataBase;
+
+import java.util.List;
+import java.util.Map;
+import java.util.stream.Collectors;
+
+/**
+ * <p>
+ *    groupingBy(): grouping elements according to a
+ *    classification function, and returning the results in a {@code Map<K, V>}
+ *
+ * @apiNote  There are 3 different versions of groupingBy().
+ *      <ul>
+ *          <li> groupingBy(classifier) : basically what is a classification value that needs to be applied to stream input.</li>
+ *          <li> groupingBy(classifier, downstream) : downstream is another collector of any type </li>
+ *          <li> groupingBy(classifier, supplier, downstream) : supplier which is used to override the default map factory</li>
+ *      </ul>
+ *
+ * </p>
+ * grouping elements according to a
+ * classification function, and returning the results in a {@code Map}
+ */
+public class StreamsGroupingByExample {
+
+    public static void main(String[] args) {
+
+        System.out.println("Student grouped based on Gender : " + groupingByExample1());
+        System.out.println("Student grouped based on PASS/FAIL : " + groupingByExample2());
+    }
+
+    /**
+     * <p>
+     *     Group the Student Based on their Gender
+     * </p>
+     */
+    public static Map<String, List<Student>> groupingByExample1() {
+        return StudentDataBase.getAllStudents()
+                .stream()
+                .collect(Collectors.groupingBy(Student::getGender));
+    }
+
+
+    /**
+     * <p>
+     *     grouping Student by using a customized implementation (i.e. based on PASS ond FAIL )
+     * </p>
+     * @return
+     */
+    public static Map<String, List<Student>> groupingByExample2() {
+        return StudentDataBase.getAllStudents()
+                .stream()
+                .collect(Collectors.groupingBy(student -> student.getGpa() >= 3.8 ? "PASS" : "FAIL"));
+    }
+}
diff --git a/README.md b/README.md
@@ -48,6 +48,7 @@ This repository contains the basic &amp; advance level examples related to Java
     * [ mapping()](Modern-Java-Examples/src/com/learn/streams_terminal/StreamsMappingExample.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)
     
 
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