Python generators in Java?

Alan Kennedy alanmk at
Mon Nov 15 17:44:46 CET 2004

[Robert Oschler]
 > Preamble:
 > - I know this is the Python forum
 > - I know about (and have used) Jython
 > I already posted this question in  But after a week I
 > have still not received a single reply.
 > One of my favorite Python features is generators.  I have to use Java
 > for one particular project (it happens).  I would like to have
 > something at least close to Python's generators for the project.

Hi Robert,

Hmm, I don't see a direct question in your post, so I'll just assume 
that you're generally inquiring about generator style functionality in java.

If you're looking to achieve the execution efficiency of python 
generators, e.g. in terms of processing sequences one value at a time 
rather than generating the entire sequence and then processing, then you 
should look at java iterators, which are designed specifically for this 

Note that java 1.5 brings new syntactic features which support 
iterators, e.g. short-hand for loops like this

public int sumArray(int array[]) {
   int sum = 0;
   for(int i : array) {
     sum += i;
   return sum;

Quite pythonic, IMHO.

However, if you're looking for the resumable-functions aspect of 
generators, you're out of luck: java doesn't not support them. But note 
that a java iterator will still very likely be more efficient than a 
python generator, albeit that the code won't be as clean.

Note that there is a currently a proposal from the codehaus people to 
add continuations to java, which could make both generators and full 
coroutines possible in java.

Lastly, it would probably be easier to discuss this subject if you gave 
an example of the type of thing you want to do, and some reasons why you 
want to do it that way. Post some python: maybe the java would be 


alan kennedy
email alan:    

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