Collections

//-------------- Person.java -----------------

public class Person {

    private String name;
    private double weight;
    private double height;

    public Person(String name, double weight, double height) {
        this.name = name;
        this.weight = weight;
        this.height = height;
    }

    public Person() {
        this("", 0, 0);
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public double getWeight() {
        return weight;
    }

    public void setWeight(double weight) {
        this.weight = weight;
    }

    public double getHeight() {
        return height;
    }

    public void setHeight(double height) {
        this.height = height;
    }

    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", weight=" + weight +
                ", height=" + height +
                '}';
    }
}

//------------------- CompareByName.java ---------------------------------

import java.util.Comparator;

public class CompareByName implements Comparator<Person> {

    @Override
    public int compare(Person o1, Person o2) {
        return o1.getName().compareTo(o2.getName());
    }
}

//------------------ CompareByHeight ---------------------------------

import java.util.Comparator;

public class CompareByHeight implements Comparator<Person> {
    @Override
    public int compare(Person o1, Person o2) {
        if(o1.getHeight() < o2.getHeight()) {
            return -1;
        } else if(o1.getHeight() > o2.getHeight()) {
            return 1;
        } else {
            return 0;
        }
    }
}

//---------------------------------- CompareByWeight ----------------------------

import java.util.Comparator;

public class CompareByWeight implements Comparator<Person> {
    @Override
    public int compare(Person o1, Person o2) {
        if(o1.getWeight() < o2.getWeight()) {
            return -1;
        } else if(o1.getWeight() > o2.getWeight()) {
            return 1;
        } else {
            return 0;
        }
    }
}

//----------------------------------- Collection.java (Main class) ---------------------

import java.util.Set;
import java.util.TreeSet;

public class Collection {

    public static void main(String[] args) {
        Person p1 = new Person("Eran", 90.5, 1.84);
        Person p4 = new Person("Ofri", 42.5, 1.54);
        Person p2 = new Person("Noa", 33.5, 1.32);
        Person p5 = new Person("Hadar", 16.5, 1.12);
        Person p3 = new Person("Inbar", 12.5, 1.65);

        Set[] sortedPersons = new Set[3];

        sortedPersons[0] = new TreeSet<Person>(new CompareByName());
        sortedPersons[1] = new TreeSet<Person>(new CompareByHeight());
        sortedPersons[2] = new TreeSet<Person>(new CompareByWeight());
        for(int i = 0; i < sortedPersons.length; i+=1) {
            sortedPersons[i].add(p1);
            sortedPersons[i].add(p2);
            sortedPersons[i].add(p3);
            sortedPersons[i].add(p4);
            sortedPersons[i].add(p5);
        }

        System.out.println("Sorted by name: " + sortedPersons[0]);
        System.out.println("Sorted by height: " + sortedPersons[1]);
        System.out.println("Sorted by weight: " + sortedPersons[2]);
    }
}