Java 8: Method as parameter with Lambda reference

Question

I have scanned serveral links but didn't find an easy solution for Java 8 Lambda expression. The most useful hint I've found was on Java 8 Lambdas but did NOT really satisfy my interest.

I want to achieve a reoccuring pattern in my code:

List<?> content=retrieveContent(strFilter);
if (!content.isEmpty())
 setField1(content.get(0));

and I would like to have it simple as

retrieveContent(strFilter, this::setField1) but somehow I don't get syntax properly - especially for the method. I can do it as a String and call if via method, but than its prone to typos... Any other ideas?

• m0skit0: How do you know setField1() method is available?

Answer 1

It sounds like you're looking for a Consumer, which will work as long as you fill in the generics with a value other than <?>.

For example:

private List<Object> retrieveContent(String strFilter, Consumer<Object> firstItemConsumer) {
 List<Object> list = new ArrayList<>();
 // Build the return...
 if(!list.isEmpty()) {
 firstItemConsumer.accept(list.get(0));
 }
 return list;
}

Can then be called with:

List<Object> content = retrieveContent(strFilter, this::setField1);

• John Bollinger: And of course, instead of <Object>, one could reference a type parameter of the host class, or a type parameter of the method if the method were made generic.
• LeO: Thx, this works basically the way as expected :-) Except that JPA does NOT like Lambda-stuff (at least for EclipseLink 2.5x)