This bug was found by St.Petersburg Java SQE team (by Alexander Kuzmin).

The java_io.DataOutputStream constructor DataOutputStream(OutputStream out)
accepts and doesn't check null parameter. Therefore, both write(int) and
write(byte[],int,int) methods throw non-documented NullPointerException.


For example, the specification for java.io.DataOutputstream.write(int) says:

The Java Language Specification Version 1.0:

22.21.3 public void write(int b) throws IOException
The byte for this operation (the low eight bits of the argument b) is written
 to the contained output stream. If no exception is thrown, the counter
 written is incremented by 1.

Implements the write method of OutputStream (§22.15.1).
_______________________Example ______________________________________
import java.io.*;

public class bug_tests {

  public static void main( String argv[] ) {

 DataOutputStream y1;
 byte b='1';
 
   y1 = new DataOutputStream(null);// Create DataOutputStream object
                                   // The constructor permit this.

  if ( (y1!=null) && (y1 instanceof DataOutputStream))
  {

   try {
   y1.write(b); // Try to write
   }
    catch (IOException e) // Check IOException
    {System.out.println("IOException ?!");
     return;}

    catch (Exception e) // Check other exceptions
    {System.out.println("Unexpected "+ e );
     return;
    }
  
       System.out.println("Failed - No exceptions");

   } //if ..

       System.out.println("Not object !!");

  }

}
_____________________Output_________________________________________

Unexpected java.lang.NullPointerException
____________________________________________________________________