I wrote a post on stackoverflow on how to use java.util.function.Function for simple method as parameter function.

Here is a simple example:

import java.util.function.Function;

public class Foo {

  /** Foo constructor **/
  private Foo(String parameter) {
    System.out.println("I'm a Foo " + parameter);
  }

  /** Static method `bar` from Foo class **/
  public static Foo bar(final String parameter) {
    return new Foo(parameter);
  }

  private static Function parametrisedMethod(Function<String, Foo> function) {
    return function;
  }
}

Basically you have a Foo object with a default constructor. A method bar that will be called as a parameter from the parametrisedMethod which is of type Function<String, Foo>.

• Function<String, Foo> means that the function takes a String as parameter and return a Foo.
• The Foo::bar correspond to a lambda like x -> Foo.bar(x);

Let’s see how we can use our newly parametrized method:

public static void main(String[] args) {
  parametrisedMethod(Foo::bar).apply("from a method");
}

The syntax is a bit weird, so let’s dissect it a bit:

• parametrisedMethod(Foo::bar) could be seen as:

  x -> parametrisedMethod(Foo.bar(x))
  

• The .apply("from a method") is basically to do:

  parametrisedMethod(Foo.bar("from a method"))
  

Now if you run the main() it should print out:

>> I'm a Foo from a method

We can see that it took the constructor plus the applied string and printed it all. Now that you have that Baseline you can create more complicated Function with your own types.

If you liked that consider upvoting the original answer on stackoverflow you lovely sausages. 🌭❤️