Java passing function as parameter

Question

This is my first approach to lambda expressions, function as parameter or in general functional programming...

How I can call B function in this code?

public class Fp_example<T>
{
    public static void main(String[] args)
    {
         ArrayList<String> names = new ArrayList<>(asList("A"));
         new Fp_example.b_function(names, /* (1) */);
    }

    public void b_function(ArrayList<T> l, Function<T,T> func)
    {
         l.forEach( (t) -> {func.apply(t);});
    }
}

I need to write my function in (1), or can I write another function and just call it inside (1)?

Answer 1

First of all, you should instantiate Fp_example<String> , since you are passing an ArrayList<String> to b_function .

Now, it's up to you which function to pass to the method, depending on how you wish to transform the input String s. Any lambda expression that takes a String argument and returns a String will do.

For example, you can pass a lambda expression that reverses the input String s :

new Fp_example<String> ().b_function(names, s -> new StringBuilder(s).reverse().toString());

or

Function<String,String> a_function = s -> new StringBuilder(s).reverse().toString();
new Fp_example<String> ().b_function(names, a_function);

You might want to display the output of applying the function on the input elements, though :

public void b_function(ArrayList<T> l, Function<T,T> func)
{
     l.forEach( (t) -> {System.out.println(func.apply(t));});
}