Demo method.
Set objectSet = new HashSet();
objectSet.add(new Integer(5));
objectSet.add(new String("Hardcore Java"));
objectSet.add(new Float(22.5f));
objectSet.add(new JPanel());
objectSet.add(new Character('x"));
objectSet.add(new ArrayList());
objectSet.add(new Double(354.5676));
objectSet.add(null);
OBJECT_SET = Collections.unmodifiableSet(objectSet);
final Iterator iter = OBJECT_SET.iterator();
Object obj = null;
while (iter.hasNext()) {
obj = iter.next();
if (obj instanceof Number) {
System.out.println(obj);
}
}