DefaultsMethodsExample2.java

package com.learn.defaults;

import com.learn.data.Student;
import com.learn.data.StudentDataBase;

import java.util.Comparator;
import java.util.List;
import java.util.function.Consumer;

public class DefaultsMethodsExample2 {

    static Consumer<Student> studentConsumer = System.out::println;
    static Comparator<Student> nameComparator = Comparator.comparing(Student::getName);
    static Comparator<Student> gpaComparator = Comparator.comparingDouble(Student::getGpa);
    static Comparator<Student> gradeComparator = Comparator.comparingInt(Student::getGradeLevel);


    public static void main(String[] args) {

        List<Student> studentList = StudentDataBase.getAllStudents();
        System.out.println("Before Sorting");
        studentList.forEach(studentConsumer);

        sortByName(studentList);

        sortByGpa(studentList);

        comparatorChain(studentList);

        sortWithNullValues(studentList);
    }

    public static void sortByName(List<Student> studentList) {
        System.out.println("Sorting By using name");
        studentList.sort(nameComparator);
        studentList.forEach(studentConsumer);
    }

    public static void sortByGpa(List<Student> studentList) {
        System.out.println("Sorting By using GPA");
        studentList.sort(gpaComparator);
        studentList.forEach(studentConsumer);
    }

    /**
     * thenComparing(): Comparator chaining
     * Chaining 2 different comparator operations and then consolidate the result
     */
    public static void comparatorChain(List<Student> studentList) {

        System.out.println("Comparator Chaining");

        // first sort by Grade
        // So in Each grade, sort the result by their name.
        studentList.sort(gradeComparator.thenComparing(nameComparator));
        studentList.forEach(studentConsumer);
    }

    /**
     * If our collection value has null value, but we try to perform sort using comparator.
     * It will throw NullPointer Exception
     * To handle these scenarios, Comparator has handy method nulls First and nulls last.
     */
    public static void sortCollectionHavingWithNull() {
        System.out.println("List with Null");
        List<Student> studentList = StudentDataBase.getAllStudents();
        studentList.add(null);
        // comparatorChain(studentList); // throw NPE
    }

    /**
     * nullsFirst() : pushes null value at first
     * nullsLast() : null values will be pushed towards the end.
     */
    public static void sortWithNullValues(List<Student> studentList) {
        studentList.add(null);
        Comparator<Student> studentComparator = Comparator.nullsFirst(nameComparator);
        studentList.sort(studentComparator);
        studentList.forEach(studentConsumer); // prints null first.
    }
}