Question

For the code below write a public static main() method in class Student that:
- creates an ArrayList<Student> object called students
- adds 4 new Student objects to the students list, with some made up names and dates
- sort the students list by name and display the sorted collection to System.out. use function getCompByName()
- sort the students list by enrollment date and display the sorted collection to System.out. use function getCompByDate()

import java.util.Comparator;
   import java.util.Date;

   public final class Student {

   private final String name;
   private final Date enrollment_date;

   /*@invariant name != null && name.length>0; @*/ //class invariant
   /*@invariant enrollment_date != null; @*/ //class invariant
   public Student(String name, Date enrollment_date) {
   super();
  
   assert name != null : "Precondition: name != null";
   assert enrollment_date != null : "Precondition: enrollment_date != null";
   assert name.indexOf(",") != -1 : "Precondition: name.indexOf(\",\") != -1";
  
   this.name = name;
   this.enrollment_date = enrollment_date;
  
   assert getName() == name : "Postcondition: getName() == name";
   assert getEnrollment_date() == enrollment_date : "Postcondition: getEnrollment_date() == enrollment_date";
   }

   public String getName() {
   return name;
   }

   public Date getEnrollment_date() {
   return enrollment_date;
   }

   public static Comparator<Student> getCompByName =
   new Comparator<Student>(){

   @Override
   public int compare(Student o1, Student o2) {

   assert o1.name != null : "Precondition: o1.name != null";
   assert o2.name != null : "Precondition: o2.name != null";
  
   return o1.name.compareTo(o2.name);
   }

   };

   public static Comparator<Student> getCompByDate =
   new Comparator<Student>(){

   @Override
   public int compare(Student p, Student q) {

   if (p.getEnrollment_date().before(q.getEnrollment_date())) {
   return -1;
   } else if (p.getEnrollment_date().after(q.getEnrollment_date())) {
   return 1;
   } else {
   return 0;
   }
   }

   };

   }

Answer 1

Program:

import java.util.ArrayList;
import java.util.Comparator;
import java.util.Date;

public final class Student {

private final String name;
private final Date enrollment_date;

/*@invariant name != null && name.length>0; @*/ //class invariant
/*@invariant enrollment_date != null; @*/ //class invariant
public Student(String name, Date enrollment_date) {
super();
  
assert name != null : "Precondition: name != null";
assert enrollment_date != null : "Precondition: enrollment_date != null";
assert name.indexOf(",") != -1 : "Precondition: name.indexOf(",") != -1";
  
this.name = name;
this.enrollment_date = enrollment_date;
  
assert getName() == name : "Postcondition: getName() == name";
assert getEnrollment_date() == enrollment_date : "Postcondition: getEnrollment_date() == enrollment_date";
}

public String getName() {
return name;
}

public Date getEnrollment_date() {
return enrollment_date;
}

public static Comparator<Student> getCompByName =
new Comparator<Student>(){

@Override
public int compare(Student o1, Student o2) {

assert o1.name != null : "Precondition: o1.name != null";
assert o2.name != null : "Precondition: o2.name != null";
  
return o1.name.compareTo(o2.name);
}

};

public static Comparator<Student> getCompByDate =
new Comparator<Student>(){

@Override
public int compare(Student p, Student q) {

if (p.getEnrollment_date().before(q.getEnrollment_date())) {
return -1;
} else if (p.getEnrollment_date().after(q.getEnrollment_date())) {
return 1;
} else {
return 0;
}
}

};

public static void main(String args[])
{
   ArrayList<Student> al=new ArrayList<Student>();
     
   al.add(new Student("Miller",new Date(1478980869690L)));
   al.add(new Student("David",new Date(1478980867490L)));
   al.add(new Student("Jhon",new Date(1478980868950L)));
     
   al.add(new Student("Stirling",new Date(1478980876190L)));
   al.sort(getCompByName);
   System.out.println("Students list sorted by name");
   for(int i=0;i<al.size();i++)
   {
   System.out.println("Student Name:"+al.get(i).getName()+", Enrollemnt Dat:"+al.get(i).getEnrollment_date());
   }
   al.sort(getCompByDate);
   System.out.println("Students list sorted by enrollment date");
   for(int i=0;i<al.size();i++)
   {
   System.out.println("Student Name:"+al.get(i).getName()+", Enrollemnt Dat:"+al.get(i).getEnrollment_date());
   }
}
}

Output: