LambdaJ: why can't we apply operation in select clause?

Question

select(list, having(on(Integer.class).intValue() % 2, equalTo(0)));

the code above throws exception.

Answer 1

The % operation has to be evaluated before select() whereas what you want it to be evaluated for each entry. i.e. what you want is closures which is available in Java 8.

If you were using a loop you could write

for(int i: list)
    if(i % 2 == 0)
       // do something with i.

Java's syntax often makes using a loop the cleanest solution when ideally you should have a choice (its also a lot faster).

Answer 2

You'll want to define your own matcher:

Matcher<Integer> even = new Predicate<Integer>() {         
 public boolean apply(Integer item) {                 
 return item % 2 == 0;         
} };

Adapted from:http://code.google.com/p/lambdaj/wiki/LambdajFeatures