Name: dbT83986 Date: 02/15/99


The real problem is that Classes are being stored in a HashMap container, and when the fully qualified Class name is hashed,
unique names result in the same hash code.

A simple example of this is:

public class Badhash
{
public static void main( String[] args )
{
String a = "CybTestClassA";
String b = "CybTestClassB";
String c = "CybTestClassC";
String d = "CybTestClassD";
String e = "suhs.CybTestClassA";
String f = "suhs.CybTestClassB";
String g = "suhs.CybTestClassC";
String h = "suhs.CybTestClassD";

System.out.println("Hashcode value for " + a + ": " + a.hashCode());
System.out.println("Hashcode value for " + b + ": " + b.hashCode());
System.out.println("Hashcode value for " + c + ": " + c.hashCode());
System.out.println("Hashcode value for " + d + ": " + d.hashCode());
System.out.println("Hashcode value for " + e + ": " + e.hashCode());
System.out.println("Hashcode value for " + f + ": " + f.hashCode());
System.out.println("Hashcode value for " + g + ": " + g.hashCode());
System.out.println("Hashcode value for " + h + ": " + h.hashCode());
}
}

Gives output:

C:\Java>java Badhash
Hashcode value for CybTestClassA: -424829519
Hashcode value for CybTestClassB: -424829518
Hashcode value for CybTestClassC: -424829517
Hashcode value for CybTestClassD: -424829516
Hashcode value for suhs.CybTestClassA: 396812414
Hashcode value for suhs.CybTestClassB: 396812414
Hashcode value for suhs.CybTestClassC: 396812414
Hashcode value for suhs.CybTestClassD: 396812414

Obviously the last 4 should each be unique!

A more specific example where the class name is used to hash:
WITH the package keyword:

package suhs;

public class Suhs
{
public static void main( String[] args )
{
CybTestClassA a = new CybTestClassA();
CybTestClassB b = new CybTestClassB();
CybTestClassC c = new CybTestClassC();
CybTestClassAA aa = new CybTestClassAA();
CybTestClassBB bb = new CybTestClassBB();
CybTestClassCC cc = new CybTestClassCC();
CybTestClassAAA aaa = new CybTestClassAAA();
CybTestClassBBB bbb = new CybTestClassBBB();
CybTestClassCCC ccc = new CybTestClassCCC();
CybTestClassAAAA aaaa = new CybTestClassAAAA();
CybTestClassBBBB bbbb = new CybTestClassBBBB();
CybTestClassCCCC cccc = new CybTestClassCCCC();
CybTestClassAAAAA aaaaa = new CybTestClassAAAAA();
CybTestClassBBBBB bbbbb = new CybTestClassBBBBB();
CybTestClassCCCCC ccccc = new CybTestClassCCCCC();
CybTestClassAAAAAA aaaaaa = new CybTestClassAAAAAA();
CybTestClassBBBBBB bbbbbb = new CybTestClassBBBBBB();
CybTestClassCCCCCC cccccc = new CybTestClassCCCCCC();
CybTestClassAAAAAAA aaaaaaa = new CybTestClassAAAAAAA();
CybTestClassBBBBBBB bbbbbbb = new CybTestClassBBBBBBB();
CybTestClassCCCCCCC ccccccc = new CybTestClassCCCCCCC();
CybTestClassAAAAAAAA aaaaaaaa = new CybTestClassAAAAAAAA();
CybTestClassBBBBBBBB bbbbbbbb = new CybTestClassBBBBBBBB();
CybTestClassCCCCCCCC cccccccc = new CybTestClassCCCCCCCC();

System.out.println("Hashcode value for '" + a.getClass().getName() + "':" + a.getClass().getName().hashCode());
System.out.println("Hashcode value for '" + b.getClass().getName() + "':" + b.getClass().getName().hashCode());
System.out.println("Hashcode value for '" + c.getClass().getName() + "':" + c.getClass().getName().hashCode());
System.out.println("Hashcode value for '" + aa.getClass().getName() + "':" + aa.getClass().getName().hashCode());
System.out.println("Hashcode value for '" + bb.getClass().getName() + "':" + bb.getClass().getName().hashCode());
System.out.println("Hashcode value for '" + cc.getClass().getName() + "':" + cc.getClass().getName().hashCode());
System.out.println("Hashcode value for '" + aaa.getClass().getName() + "':" + aaa.getClass().getName().hashCode());
System.out.println("Hashcode value for '" + bbb.getClass().getName() + "':" + bbb.getClass().getName().hashCode());
System.out.println("Hashcode value for '" + ccc.getClass().getName() + "':" + ccc.getClass().getName().hashCode());
System.out.println("Hashcode value for '" + aaaa.getClass().getName() + "':" + aaaa.getClass().getName().hashCode());
System.out.println("Hashcode value for '" + bbbb.getClass().getName() + "':" + bbbb.getClass().getName().hashCode());
System.out.println("Hashcode value for '" + cccc.getClass().getName() + "':" + cccc.getClass().getName().hashCode());
System.out.println("Hashcode value for '" + aaaaa.getClass().getName() + "':" + aaaaa.getClass().getName().hashCode());
System.out.println("Hashcode value for '" + bbbbb.getClass().getName() + "':" + bbbbb.getClass().getName().hashCode());
System.out.println("Hashcode value for '" + ccccc.getClass().getName() + "':" + ccccc.getClass().getName().hashCode());
System.out.println("Hashcode value for '" + aaaaaa.getClass().getName() + "':" + aaaaaa.getClass().getName().hashCode());
System.out.println("Hashcode value for '" + bbbbbb.getClass().getName() + "':" + bbbbbb.getClass().getName().hashCode());
System.out.println("Hashcode value for '" + cccccc.getClass().getName() + "':" + cccccc.getClass().getName().hashCode());
System.out.println("Hashcode value for '" + aaaaaaa.getClass().getName() + "':" + aaaaaaa.getClass().getName().hashCode());
System.out.println("Hashcode value for '" + bbbbbbb.getClass().getName() + "':" + bbbbbbb.getClass().getName().hashCode());
System.out.println("Hashcode value for '" + ccccccc.getClass().getName() + "':" + ccccccc.getClass().getName().hashCode());
System.out.println("Hashcode value for '" + aaaaaaaa.getClass().getName() + "':" + aaaaaaaa.getClass().getName().hashCode());
System.out.println("Hashcode value for '" + bbbbbbbb.getClass().getName() + "':" + bbbbbbbb.getClass().getName().hashCode());
System.out.println("Hashcode value for '" + cccccccc.getClass().getName() + "':" + cccccccc.getClass().getName().hashCode());
}
}

class CybTestClassA {}
class CybTestClassB {}
class CybTestClassC {}

class CybTestClassAA {}
class CybTestClassBB {}
class CybTestClassCC {}

class CybTestClassAAA {}
class CybTestClassBBB {}
class CybTestClassCCC {}

class CybTestClassAAAA {}
class CybTestClassBBBB {}
class CybTestClassCCCC {}

class CybTestClassAAAAA {}
class CybTestClassBBBBB {}
class CybTestClassCCCCC {}

class CybTestClassAAAAAA {}
class CybTestClassBBBBBB {}
class CybTestClassCCCCCC {}

class CybTestClassAAAAAAA {}
class CybTestClassBBBBBBB {}
class CybTestClassCCCCCCC {}

class CybTestClassAAAAAAAA {}
class CybTestClassBBBBBBBB {}
class CybTestClassCCCCCCCC {}

Gives output:

C:\Java>java suhs.Suhs
Hashcode value for 'suhs.CybTestClassA':396812414
Hashcode value for 'suhs.CybTestClassB':396812414
Hashcode value for 'suhs.CybTestClassC':396812414
Hashcode value for 'suhs.CybTestClassAA':-1704184973
Hashcode value for 'suhs.CybTestClassBB':-1704184972
Hashcode value for 'suhs.CybTestClassCC':-1704184971
Hashcode value for 'suhs.CybTestClassAAA':-1704184973
Hashcode value for 'suhs.CybTestClassBBB':-1704184972
Hashcode value for 'suhs.CybTestClassCCC':-1704184971
Hashcode value for 'suhs.CybTestClassAAAA':-2038704442
Hashcode value for 'suhs.CybTestClassBBBB':-2038704402
Hashcode value for 'suhs.CybTestClassCCCC':-2038704362
Hashcode value for 'suhs.CybTestClassAAAAA':-2038704442
Hashcode value for 'suhs.CybTestClassBBBBB':-2038704402
Hashcode value for 'suhs.CybTestClassCCCCC':-2038704362
Hashcode value for 'suhs.CybTestClassAAAAAA':2094905451
Hashcode value for 'suhs.CybTestClassBBBBBB':2094907012
Hashcode value for 'suhs.CybTestClassCCCCCC':2094908573
Hashcode value for 'suhs.CybTestClassAAAAAAA':1054564892
Hashcode value for 'suhs.CybTestClassBBBBBBB':1054564932
Hashcode value for 'suhs.CybTestClassCCCCCCC':1054564972
Hashcode value for 'suhs.CybTestClassAAAAAAAA':-1821642107
Hashcode value for 'suhs.CybTestClassBBBBBBBB':-1821640546
Hashcode value for 'suhs.CybTestClassCCCCCCCC':-1821638985

And the same thing without the package keyword gives output:

C:\Java>java Suhs
Hashcode value for 'CybTestClassA':-424829519
Hashcode value for 'CybTestClassB':-424829518
Hashcode value for 'CybTestClassC':-424829517
Hashcode value for 'CybTestClassAA':1461177046
Hashcode value for 'CybTestClassBB':1461177084
Hashcode value for 'CybTestClassCC':1461177122
Hashcode value for 'CybTestClassAAA':-1771024081
Hashcode value for 'CybTestClassBBB':-1771022674
Hashcode value for 'CybTestClassCCC':-1771021267
Hashcode value for 'CybTestClassAAAA':989624285
Hashcode value for 'CybTestClassBBBB':989624325
Hashcode value for 'CybTestClassCCCC':989624365
Hashcode value for 'CybTestClassAAAAA':-59358484
Hashcode value for 'CybTestClassBBBBB':-59356923
Hashcode value for 'CybTestClassCCCCC':-59355362
Hashcode value for 'CybTestClassAAAAAA':-59358484
Hashcode value for 'CybTestClassBBBBBB':-59356923
Hashcode value for 'CybTestClassCCCCCC':-59355362
Hashcode value for 'CybTestClassAAAAAAA':1979986485
Hashcode value for 'CybTestClassBBBBBBB':1980047365
Hashcode value for 'CybTestClassCCCCCCC':1980108245
Hashcode value for 'CybTestClassAAAAAAAA':1979986485
Hashcode value for 'CybTestClassBBBBBBBB':1980047365
Hashcode value for 'CybTestClassCCCCCCCC':1980108245

The hashcodes are different for each run as expected, but the
PATTERN of hashcode likeness is unexpectedly different (actually, any likeness is unexpected).
In the non-package run, the same hashcodes are seen near the
end of the run (
the 4 and 5 'A' are the same, the 6 and 7 'A' are the same,
the 4 and 5 'B' are the same, the 6 and 7 'B' are the same,
the 4 and 5 'C' are the same, the 6 and 7 'C' are the same).

In the package run, the same hashcodes are seen near the
beginning of the run (
the 'A', 'B', 'C' are the same,
the 2 and 3 'A' are the same, the 4 and 5 'A' are the same,
the 2 and 3 'B' are the same, the 4 and 5 'B' are the same,
the 2 and 3 'C' are the same, the 4 and 5 'C' are the same).
(Review ID: 35065)
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