Programming with RDDs - Learning Spark - page 33

We can either define our function classes inline as anonymous inner classes
( Example 3-22 ), or create a named class ( Example 3-23 ).
Example 3-22. Java function passing with anonymous inner class
RDD < String > errors = lines . filter ( new Function < String , Boolean >() {
public Boolean call ( String x ) { return x . contains ( "error" ); }
});
Example 3-23. Java function passing with named class
class ContainsError implements Function < String , Boolean >() {
public Boolean call ( String x ) { return x . contains ( "error" ); }
}
RDD < String > errors = lines . filter ( new ContainsError ());
The style to choose is a personal preference, but we find that top-level named func‐
tions are often cleaner for organizing large programs. One other benefit of top-level
functions is that you can give them constructor parameters, as shown in
Example 3-24 .
Example 3-24. Java function class with parameters
class Contains implements Function < String , Boolean >() {
private String query ;
public Contains ( String query ) { this . query = query ; }
public Boolean call ( String x ) { return x . contains ( query ); }
}
RDD < String > errors = lines . filter ( new Contains ( "error" ));
In Java 8, you can also use lambda expressions to concisely implement the function
interfaces. Since Java 8 is still relatively new as of this writing, our examples use the
more verbose syntax for defining classes in previous versions of Java. However, with
lambda expressions, our search example would look like Example 3-25 .
Example 3-25. Java function passing with lambda expression in Java 8
RDD < String > errors = lines . filter ( s -> s . contains ( "error" ));
If you are interested in using Java 8's lambda expression, refer to Oracle's documen‐
tation and the Databricks blog post on how to use lambdas with Spark .