Declaring lambdas in Java8

What would be the best practice to declare lambdas in Java8 code? How it was designed to be used?

For example, let's say that we have a method that accept a Function. I want to provide function implementation that can be reusable. So I can do this:

[A] Implement a Function interface:

public class Foo implements Function<A,B> {
    public B apply(A a) {...}
}
...
useFunction(new Foo());

[B] Declare Function as lambda in some static field:

public interface Foo {
    Function<A,B> bar = it -> { ....}
}
...
useFunction(Foo.bar);

[C] Use method reference:

public class Foo {
    public static B bar(A a) {...}
}
...
useFunction(Foo::bar);

Until functional programing in java8, I tried not to pollute code with statics. However, now I am somehow 'forced' to use statics (or global singletons) for storing reusable lambdas.