Collections - Set to prevent duplicating items

Stefan <>
Mon, 12 Jul 2010 11:38:38 -0700 (PDT)
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 + "";

 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);




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

Some refertence:

Thank you in advance

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