Can use functional operations

Question

I'm using the for-each construct in Java as follows:

public int getNumRStations() {     int numRoutes = 0;      for (ArrayList<Route> route : routes) {         numRoutes += route.size();     }      return numRoutes; } 

NetBeans shows a warning/notice that says "Can use functional operations". Upon automatically resolving it, the newly generated code shows this:

public int getNumRStations() {     int numRoutes = 0;      numRoutes = routes.stream().map((route) -> route.size()).reduce(numRoutes, Integer::sum);      return numRoutes; } 

1. Why is NetBeans warning me of this? I know I'm not supposed to blindly trust IDEs, so that's why I'm asking.
2. What is that new line supposed to do? I haven't seen anything like it, in real life or in class.

Answer 1

That looks like NetBeans suggesting refactoring your sum operation as a Java 8 "lambda" or functional programming operation using the map and reduce functions from the Stream interface. You must be using a Java 8 JDK with NetBeans.

Breaking down what it's doing:

• the "map()" function is performing a count of all of your route sizes in your routes array list,

• the "reduce()" function is then performing a sum of those individual sizes to get the final result for the total number of routes.

The map() and reduce() functions are documented in the Java 8 documentation for the Stream interface available at this link

This answer addresses "what it is" but doesn't address "why it's better". I will admit to still learning about these constructs myself.