How to sort an array using Comparable and Comparator interfaces

In order to sort an array in Java using Comparable and Comparator interfaces, first, you may create a Student class as follows :

class Student implements Comparable<Student> {

String id;

String name;

Double cgpa;

public Student(String studentId, String studentName, double studentCGPA) {

id = studentId;

name = studentName;

cgpa = studentCGPA;

}

public String toString() {

return " \n " + id + "  \t  " + name + "  \t  " + cgpa;

}

public int compareTo(Student that) {

return this.id.compareTo(that.id);

}

}

Then, you may add another class entitled ComparatorTest2 as follows :

import java.util.Arrays;

import java.util.Comparator;

class CGPAComparator implements Comparator<Student> {

    public int compare(Student s1, Student s2) {

        return (s1.cgpa.compareTo(s2.cgpa));     

    }    

}

class ComparatorTest2 {

    public static void main(String []args) {

        Student []students = {  new Student("cs011", "Lennon  ", 3.1), 

new Student("cs021", "McCartney", 3.4),  

new Student("cs012", "Harrison ", 2.7),    

new Student("cs022", "Starr ", 3.7) };

        System.out.println("Before sorting by CGPA ");

        System.out.println("Student-ID \t  Name \t  CGPA (for 4.0) ");

        System.out.println(Arrays.toString(students));

        

        Arrays.sort(students, new CGPAComparator());

        

        System.out.println("After sorting by CGPA");

        System.out.println("Student-ID \t  Name \t  CGPA (for 4.0) ");

        System.out.println(Arrays.toString(students));

    }    

}

If you run this program you would get the following output :

Before sorting by CGPA 

Student-ID  Name  CGPA (for 4.0) 

[ 

 cs011    Lennon      3.1,  

 cs021    McCartney    3.4,  

 cs012    Harrison    2.7,  

 cs022    Starr    3.7]

After sorting by CGPA

Student-ID  Name  CGPA (for 4.0) 

[ 

 cs012    Harrison    2.7,  

 cs011    Lennon      3.1,  

 cs021    McCartney    3.4,  

 cs022    Starr    3.7]

That's it, as you might have noticed, the students array was sorted according to cgpa field.