That line doesn't make any sense :) @FunctionalInterface is an annotation, you never use it like that. First off you need a type that is a function with two parameter a,b -> result. This is already present and is BiFunction. Then you need something that take a bifunction, a value and return a function with a single parameter and use the given value as the second. This something is a method: public static Function makePartial(BiFunction original, A value) { return x -> original.apply(value, x); } This take a bifunction (A,B -> R) and a value A, returns a function (B -> R) that stores A in the closure. Here's how to use: public static void main(String[] args) { BiFunction sum = (a,b) -> a+b; System.out.println(sum.apply(4, 2)); // 6 Function plusFive = makePartial(sum, 5); System.out.println(plusFive.apply(3)); // 8 } More on reddit.com

Usually I either have ugly inline try catch blocks, a private method doing the same, or I make sure the method I call only uses unchecked exceptions - but it’s not ideal and and unfortunately a posterbook example of Java's design. More on reddit.com

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When I don't remember which to use I always refer to this list . I've always felt this functional interface business is just bad design when compared with C# simple Action/Function. Another victim of type erasure. More on reddit.com