Java8 Lambda Function apply alternative syntax

Question

When using lambda function variable, is there an alternative to invoking function with apply.

Function<String, String> mesgFunction =  (name) -> "Property "+ name +" is not set in the environment";
Optional.ofNullable(System.getProperty("A")).orElseThrow(() -> new IllegalArgumentException(mesgFunction.apply("A")));
Optional.ofNullable(System.getProperty("B")).orElseThrow(() -> new IllegalArgumentException(mesgFunction.apply("B")));

Is there a shorter syntax to mesgFunction.apply("A"). I tried mesgFunction("A") which complained that the method does not exist. Am I missing something? Isn't there a shorter alternative?

Answer 1

No, the fact that an interface is a functional interface doesn’t allow any alternative calling syntax; it’s methods are invoked like any other interface method.

But you can just factor out more of the common code to shorten the repeated code

Function<String, Supplier<IllegalArgumentException>> f = name ->
    () -> new IllegalArgumentException("Property "+name+" is not set in the environment");
String valueA = Optional.of("A").map(System::getProperty).orElseThrow(f.apply("A"));
String valueB = Optional.of("B").map(System::getProperty).orElseThrow(f.apply("B"));

however, this still has no advantage over a conventional

public static String getRequiredProperty(String name) {
    String value = System.getProperty(name);
    if (value == null) {
        throw new IllegalArgumentException("Property "+name+" is not set in the environment");
    }

    return value;
}

 

String valueA = getRequiredProperty("A");
String valueB = getRequiredProperty("B");

which has the advantage of having no code duplication (esp. regarding the constants "A" and "B"), thus less room for accidental inconsistencies.

Answer 2

No, there is no alternative like that. apply() is "just" a method of the Function interface, so that method must be called. There is no syntactic sugar to make that more concise.