Java 8 Collectors: reducing Example

public static <T> Collector<T,?,Optional<T>> reducing(BinaryOperator<T> op) 

package com.concretepage.util;
public class Student {
    private String name;
    private Integer age;
    private String className;
    public Student(String name,Integer age, String className){
        this.name=name;
        this.age=age;
        this.className = className;
    }
    public String getName() {
        return name;
    }
    public Integer getAge() {
        return age;
    }
    public String getClassName() {
        return className;
    }
}  

package com.concretepage.util;
import java.util.Arrays;
import java.util.Comparator;
import java.util.List;
import java.util.Map;
import java.util.Optional;
import java.util.function.BinaryOperator;
import java.util.stream.Collectors;
public class ReducingDemo {
    public static void main(String[] args) {
        Student s1 = new Student("Shyam", 22,"A");
        Student s2 = new Student("Ram",23,"A");
        Student s3 = new Student("Mohan",22,"B");
        Student s4 = new Student(null,21,"B");
        List<Student> list = Arrays.asList(s1,s2,s3,s4);
        Comparator<Student> ageComparator = Comparator.comparing(Student::getAge); 
        Map<String, Optional<Student>> eldestByClass = list.stream().collect(Collectors.groupingBy(Student::getClassName, 
                Collectors.reducing(BinaryOperator.maxBy(ageComparator))));
        eldestByClass.forEach((k,v)->System.out.println("Class:"+k+" Age:"+
                ((Optional<Student>)v).get().getAge()+" Name:"+((Optional<Student>)v).get().getName()));
    }
} 

Class:A Age:23 Name:Ram
Class:B Age:22 Name:Mohan