import java.util.ArrayList;
import java.util.Collections;

public class Vertex implements Comparable<Vertex> {

  public final int id; 

  public Vertex(int id) {
    this.id = id;
  }

  @Override
  public int compareTo(Vertex o) {
    return id - o.id;
  }

  @Override
    public String toString() {
    return ""+id;
  }

  /** Vergleichbarkeit von Knoten testen durch Sortierung */
  public static void main(String[] args) {
    Vertex v1 = new Vertex(1);
    Vertex v2 = new Vertex(2);
    ArrayList<Vertex> test = new ArrayList<>();
    test.add(v1);
    test.add(v2);
    Collections.sort(test);
    System.out.println(test);
  }
}