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));
}
Yes, the enhanced for statement uses Iterator under-the-covers for iterable collections, see Section 14.14.2 of the JLS:
ReplyDeleteIf 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.
The for-each loop in Java uses the underlying iterator mechanism. So to answer your question, the code is identical.
ReplyDeleteThis is most likely not a bottleneck in your code. You should identify the top 10 method hotspots using JProfiler and find out how to optimize those method calls.
The for-each statement uses the iterator to iterate over your collection. The compiler replaces your for-each with a while loop.
ReplyDelete