JAVA Comparator in FOR-Schleife

public class Student {

	private int nr;
	private String name;
	private int alter;
	private double note;
	
	public Student(int nr, String name, int alter, double note) {
		this.name = name;
		this.alter = alter;
		this.nr = nr;
		this.note = note;
	}

	public double getNote() {
		return note;
	}

	public void setNote(double note) {
		this.note = note;
	}

	public int getNr() {
		return nr;
	}

	public String getName() {
		return name;
	}

	public int getAlter() {
		return alter;
	}
}

import java.util.Comparator;

/**
 * Sortierung nach Noten
 */
public class SortNoten implements Comparator<Student>{

	@Override
	public int compare(Student s1, Student s2) {
		// Die Notenwerte werden zu Double gewandelt, 
		// damit die Methode compareTo genutzt werden kann
		Double d1 = s1.getNote();
		Double d2 = s2.getNote();
		return d1.compareTo(d2);
	}
}

import java.util.Comparator;

/**
 * Sortierung nach Alter
 */
public class SortAlter implements Comparator<Student>{

	@Override
	public int compare(Student s1, Student s2) {
		Integer a1 = s1.getAlter();
		Integer a2 = s2.getAlter();
		return a1.compareTo(a2);
	}
}

import java.util.ArrayList;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;

public class StudentExample {
	private static List<Student> students = new ArrayList<Student>();
	
	public static void main(String args) {
		students.add(new Student(4, "Archimedes Syrakus", 2296, 6.0));  
		students.add(new Student(3, "Fritzli Schneider", 9, 5.9));  
		students.add(new Student(1, "Walterli Tell junjun.", 12, 4.3));  
		students.add(new Student(6, "Greengrey vonRotz", 20, 3.7));  
		students.add(new Student(5, "Maria Stuart", 467, 2.9));  
		
		System.out.printf("Nach Noten sortiert:%n");  
		Collections.sort(students, new SortNoten());
		Iterator<Student> itr = students.iterator();
		Student s;
		while (itr.hasNext()) {
			s = itr.next();
			System.out.printf("Student %s, Note %.2f%n", s.getName(), s.getNote());  
		}
		
		System.out.print("%n");  
		System.out.printf("Nach Alter sortiert:%n");  
		Collections.sort(students, new SortAlter());
		itr = students.iterator();
		while (itr.hasNext()) {
			s = itr.next();
			System.out.printf("Student %s, Alter %d%n", s.getName(), s.getAlter());  
		}
	}
}