Listing 1:

 An inefficient, but correct, primary key class

 public class MyPk

    implements java.io.Serializable

 {

    public String str;

    public int i;

    public byte b;

    public MyPk() {}

    public int hashCode() { return -1; }

    public boolean equals(Object o) {

      if ((o != null) && (MyPk.class.equals(o.getClass()))) {

        MyPk other = (MyPk) o;

        return other.str.equals(str) && other.i == i && other.b == b;

      } else {

        return false;

      }

    }

 }

 

 Listing 2:

 An efficient equals implementation

 public final class MyPk ...

    public boolean equals(Object o) {

      if (o == this) return true;

      if (o instanceof MyPk) {

        MyPk other = (MyPk) o;

        return other.hashCode() == hashCode() &&

          other.i == i && other.b == b &&

          other.str.equals(str);

      } else {

        return false;

      }

    }