A program for printing the list of students with their roll number, name, marks and grade using predefined functional interfaces.

Predefined-Interfaces-Example.java

import java.util.Arrays;
import java.util.List;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.function.Supplier;

class Student {
    //roll number assigner used by supplier
    static int rollNoAssigner;
    //student properties
    int rollNo;
    String name;
    int marks;
    String grade;

    //for initializing student with name and marks
    Student(String name, int marks) {
        this.name = name;
        this.marks = marks;
    }
}

class FunctionalInterface {
    public static void main(String[] args) {
        //Function used to assign grades to students
        Function<Student, String> getGrade = student -> {
            String grade = "";
            if (student.marks > 90) grade = "A";
            else if (student.marks > 80) grade = "B";
            else if (student.marks > 70) grade = "C";
            else if (student.marks > 60) grade = "D";
            else if (student.marks > 50) grade = "E";
            else grade = "F";
            return grade;
        };
        
        //Supplier used to supply roll number to the student on FIFO basis
        Supplier<Integer> assignRollNo = () -> ++Student.rollNoAssigner;

        //Predicate used to filter students whose marks is greater than 80 
        Predicate<Integer> filterStudent = marks -> marks >= 80;

        //Consumer used to print student details
        Consumer<Student> printStudents = student -> {
            student.rollNo = assignRollNo.get();
            student.grade = getGrade.apply(student);
            System.out.println("RollNo : " + student.rollNo);
            System.out.println("Name : " + student.name);
            System.out.println("Marks : " + student.marks);
            System.out.println("Grades : " + student.grade + "\n");
        };

        List<Student> list = Arrays.asList(new Student("divyanshu", 78), new Student("akash", 61), new Student("aditya", 43), new Student("jatin", 94), new Student("yatharth", 88));
        for (Student student : list) {
            if (filterStudent.test(student.marks)) {
                printStudents.accept(student);
            }
        }
    }
}