Question

I was using JProfiler for profiling of my application, as it is a huge application so I am very aware of its performance and efficiency.
It was taking too long so I replace all Iterator.hasNext with for-each but when I am seeing in the JProfilers CPU view it is showing me Iterator.hasNext method called where I am using for-each.
Why does so? Is there any relation between these two?
Here is the example code :

    List<Map<String, Object>> mapList = jdbcTemplate
                        .queryForList(MAP.SELECT_ALL);
                for (Map<String, Object> map : mapList) {
            list.add(fillPreferenceMaster(preferenceMasterMap));
}

Answer 1

Yes, the enhanced for statement uses Iterator under-the-covers for iterable collections, see Section 14.14.2 of the JLS:

If the type of Expression is a subtype of Iterable, then let I be the type of the expression Expression.iterator(). The enhanced for statement is equivalent to a basic for statement of the form:

for (I #i = Expression.iterator(); #i.hasNext(); ) {
        VariableModifiersopt Type Identifier = #i.next();
   Statement
}

Where #i is a compiler-generated identifier that is distinct from any other identifiers (compiler-generated or otherwise) that are in scope (§6.3) at the point where the enhanced for statement occurs.