}

}

> 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)

Stefan wrote:
>   Set vertices = new HashSet();
> [3, 2, 3] (Vertex was added to set althought it equals another Vertex)

Stefan wrote:
> 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);
>  }
> }

> On 7/12/2010 2:38 PM, Stefan wrote:

> > 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)

>      "I observed immediately that the malefactor had made one crucial
> error in carrying out his fiendish plan: He forgot to override the
> hashCode() method when overriding equals().  As any student of the art
> of detection knows well, these two are inseparable: Override both, or
> override neither, or invoke chaos upon yourself -- as many a resident
> of Her Majesty's Gaols can testify tearfully."

>      "Astounding, Holmes!"

>      "Elementary, my dear Watson.  I also note that this perpetrator is
> a particularly clumsy example of the species, having implemented an
> equals() that fails miserably if given an argument that is `null', say,
> or a reference to anything other than a `Vertex' instance.  Like so many
> of the criminal underclass, he fails to consider the consequences of his
> actions in a wider context than his immediate plot."

>      "The criminal `underclass', Holmes?  Surely you meant `subclass'."

>      "You're starting to get on my nerves, Watson.  Must I uncase my
> violin again?"

>      "I say, Holmes, I believe I'll go out for a bit of a stroll."

> --
> Eric Sosman
> esos...@ieee-dot-org.invalid