mapping() terminal operations

spdpiyush · spdpiyush · commit 073ec4978564 · 2025-03-05T15:22:00.000+05:30
diff --git a/Modern-Java-Examples/src/com/learn/data/StudentDataBase.java b/Modern-Java-Examples/src/com/learn/data/StudentDataBase.java
@@ -32,12 +32,15 @@ public static List<Student> getAllStudents() {
         Student student5 = new Student("Sophia", 4, "female", 3.5, Arrays.asList("swimming", "basketball", "dancing"), 15);
         Student student6 = new Student("James", 4, "male", 3.2, Arrays.asList("swimming", "basketball"), 5);
 
+        Student student7 = new Student("Adam", 5, "male", 5.2, Arrays.asList("swimming", "basketball"), 4);
+
         studentList.add(student1);
         studentList.add(student2);
         studentList.add(student3);
         studentList.add(student4);
         studentList.add(student5);
         studentList.add(student6);
+        studentList.add(student7);
         return studentList;
     }
 }
diff --git a/Modern-Java-Examples/src/com/learn/streams_terminal/StreamsMappingExample.java b/Modern-Java-Examples/src/com/learn/streams_terminal/StreamsMappingExample.java
@@ -0,0 +1,73 @@
+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.Set;
+import java.util.stream.Collectors;
+
+/**
+ * <p>
+ *     <code>mapping()</code> Collector applies a transformation function first and then
+ *     collects the data in a collection ( could be any type of collection )
+ *     it takes 2 input :
+ *     First is the Function, which is a mapper and second is a downstream which represents
+ *     a type of collection which we want the result to be collected.
+ *
+ * </p>
+ */
+public class StreamsMappingExample {
+
+    public static void main(String[] args) {
+
+        System.out.println("Student Name List : " + mapping1());
+
+        System.out.println("Student Name Set : " + mapping2());
+
+        System.out.println("Student Names for each Grade : " + gradeToStudentName());
+    }
+
+    /**
+     * this is going to collect List of Students Name i.e type String
+     * @return
+     */
+    public static List<String> mapping1() {
+        return StudentDataBase.getAllStudents().stream()
+                .collect(Collectors.mapping(Student::getName, Collectors.toList()));
+    }
+
+    /**
+     * this is going to collect Set of Students Name i.e type String
+     * @return
+     */
+    public static Set<String> mapping2() {
+        return StudentDataBase.getAllStudents().stream()
+                .collect(Collectors.mapping(Student::getName, Collectors.toSet()));
+    }
+
+    /**
+     * @apiNote
+     *      The {@code mapping()} collectors are most useful when used in a
+     *      multi-level reduction, such as downstream of a {@code groupingBy} or
+     *       {@code partitioningBy}.  For example, given a stream of
+     *       {@code Person}, to accumulate the set of last names in each city:
+     *       <pre>{@code
+     *       Map<City, Set<String>> lastNamesByCity
+     *         = people.stream().collect(
+     *           groupingBy(Person::getCity,
+     *                      mapping(Person::getLastName,
+     *                              toSet())));
+     *       }</pre>
+     */
+    public static Map<Integer, List<String>> gradeToStudentName() {
+        return StudentDataBase.getAllStudents().stream()
+                .collect(
+                        Collectors.groupingBy(Student::getGradeLevel,
+                                Collectors.mapping(Student::getName, Collectors.toList())
+                        )
+                );
+    }
+
+}
diff --git a/README.md b/README.md
@@ -45,6 +45,7 @@ This repository contains the basic &amp; advance level examples related to Java
   * [ Stream Terminal Operations ](Modern-Java-Examples/src/com/learn/streams_terminal)
     * [ joining()](Modern-Java-Examples/src/com/learn/streams_terminal/StreamsJoiningExample.java)
     * [ counting()](Modern-Java-Examples/src/com/learn/streams_terminal/StreamsCountingExample.java)
+    * [ mapping()](Modern-Java-Examples/src/com/learn/streams_terminal/StreamsMappingExample.java)
     
 
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