[snip]

Thank you Andrew.

Are the assignments of arg1 & arg2 to null unnecessary here?

public class TestClass {

   public TestClass(long arg1, long arg2)
   throws IllegalArgumentException {
       if (arg1 > 0xffffffffL || arg1 < 0 || arg2 > 0xffffffffL || arg2 <
0) {
           this.arg1 = null;
           this.arg2 = null;
           throw new IllegalArgumentException();
       }
       else {
           this.arg1 = arg1;
           this.arg2 = arg2;
       }
   }
   public Long getArg1() {
       return arg1;
   }
   public Long getArg2() {
       return arg2;
   }
   private final Long arg1;
   private final Long arg2;
}

If you don't need to do any value-checking, you can have it both ways.

<code>
class PairOfInts {
 public int x, y;

 public PairOfInts setX(int newX) {
   this.x = newX;
   return this;
 }

 public PairOfInts setY(int newY) {
   this.y = newY;
   return this;
 }

 public PairOfInts setBoth(int newX, int newY) {
   this.x = newX;
   this.y = newY;
   return this;
 }
}
</code>

   If you DO need value checking... well... don't make the fields public.

   - Oliver

Sorry for the hasty post.
This does compile, and I guess
that adding a Tag with a TagMeta
with null values doesn't really matter.
I can just test for that. In fact, it seems
not to apply to the situation you described.
Thanks.
Jeff

package higgins.jeff.test;

import java.util.ArrayList;

public class TagDemo {

 public static void main(String[] args) {
       ArrayList<Tag> list = new ArrayList<Tag>();
       int tag = 257;
       long count = -0xffffffffL & 0xffffffffL;
       long value = 0xffffffffL & 0xffffffffL;
       try {
         list.add(new Tag(tag, value, count));
       }
       catch(Exception e) { e.printStackTrace(); }
       if (list.get(0).getTag() == null) {
         System.out.println("Found unknown tag.");
       }
       else {
         System.out.println(list.get(0).getName() + ".tag = " +
list.get(0).getTag());
         System.out.println(list.get(0).getName() + ".value = " +
list.get(0).getValue());
         System.out.println(list.get(0).getName() + ".count = " +
list.get(0).getCount());
         System.out.println(list.get(0).getName() + ".shortDescription = "
+ list.get(0).getShortDescription());
       }
 }
}

package higgins.jeff.test;

import java.util.HashMap;
import java.lang.reflect.Constructor;

public class Tag {

 public Tag(Integer tag, Long value, Long count) throws Exception {
       initializeMap();
       if (value > 0xffffffffL || value < 0 || count > 0xffffffffL || count
< 0) {
           throw new IllegalArgumentException();
       }
       else {
           if (isKnownTag(tag)) {
               Class _class = Class.forName("higgins.jeff.test." +
tagMap.get(tag));
               Constructor _constr = _class.getConstructor(
                   new Class[] {Integer.class, Long.class, Long.class});
               meta = (TagMeta)_constr.newInstance(new Object[] {tag,
value, count});
           }
           else meta = new TagMeta(null, null, null);
       }
   }
 public Integer getTag() {
   return meta.getTag();
 }
   public Long getValue() {
     return meta.getValue();
   }
 public Long getCount(){
     return meta.getCount();
   }
 public String getName() {
   return meta.getName();
 }
 public String getShortDescription() {
     return meta.getShortDescription();
   }
   private final TagMeta meta;
   public static final HashMap<Integer, String> tagMap = new
HashMap<Integer, String>();
   public static final Boolean isKnownTag(Integer tag) {
       return tagMap.containsKey(tag);
   }
   public static final void initializeMap() {
       tagMap.put(256, "ImageWidth");
   }
}

package higgins.jeff.test;

public class TagMeta {
 public TagMeta(Integer tag, Long value, Long count) {
   this.tag = tag;
   this.value = value;
   this.count = count;
 }

 public Integer getTag() {
   return null;
 }

 public Long getValue() {
   return value;
 }

 public Long getCount() {
   return count;
 }

 public String getName() {
   return null;
 }

 public String getShortDescription() {
   return null;
 }
 private final Integer tag;
 private final Long value;
 private final Long count;
}

package higgins.jeff.test;

public class ImageWidth extends TagMeta {
 public ImageWidth(Integer tag, Long value, Long count) {
   super(tag, value, count);
 }

 @Override
 public Integer getTag() {
   return tag;
 }

 @Override
 public String getName() {
   return name;
 }

 @Override
 public String getShortDescription() {
   return shortDescription;
 }

 private final Integer tag = 256;

 private final String name = "ImageWidth";

 private final String shortDescription = "The number of columns in the
image, "
     + "i.e. the number of pixels per row.";
}