Re: Collections - Set to prevent duplicating items

Hello,
I guess my problem is "no-brainer" to some of you, but for now I fell
completely helpless. Here is an easiest example:

package test;
import java.util.*;

class Vertex {
  int number;

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

  public String toString() {
   return number + "";
  }

  @Override
  public boolean equals(Object obj) {
   return this.number == ((Vertex) obj).number;
  }
}

public class SetTest {
  public static void main(String[] args) {
   Set vertices = new HashSet();

   Vertex a = new Vertex(2);
   Vertex b = new Vertex(3);
   Vertex c = new Vertex(3);

   System.out.println(b.equals(c));

   vertices.add(a);
   vertices.add(b);
   vertices.add(c);

   System.out.println(vertices);
  }
}

Console prints:
true (b equals c)
[3, 2, 3] (Vertex was added to set althought it equals another Vertex)