Creating Predicates on the fly

Question

I have a String[] of user input and I want to filter a Collection of devices based on if the hostName of the device contains any of the user input.

I'm trying to follow the lesson https://docs.oracle.com/javase/tutorial/java/javaOO/lambdaexpressions.html to do this.

interface PredicateOperation{
    Predicate operation(String[] input);
}

public Predicate getPredicate(String[] input, PredicateOperation op){
    return op.operation(input);
}

private TufinDeviceCollection<TufinDevice> filter(TufinDeviceCollection<TufinDevice> devices) {        

       //Check if any HostNames of the devices contain any of the items in String[] modelContains

            devices = devices.stream()
                    .sequential()
                    .filter(//How do i create this predicate?)//we need to create the lamda expression to evaulate if the hostName of device d contains any of the items String[] userInput
                    .collect(Collectors.toCollection(TufinDeviceCollection<TufinDevice>::new));

    }

It is unclear to me how to define the PredicateOperation that goes in .filter(..)

Answer 1

.filter(device -> Arrays.stream(userInput)
                        .anyMatch(input -> device.getHostName().contains(input)))

But you need String[] userInput to be accessible from the filter method.

I guess it was an attempt to write own @FunctionalInterface to replace the standard Predicate<T>.

interface PredicateOperation {
    Predicate operation(String[] input);
}

It's not very practical, though.

PredicateOperation operation = (String[] input) -> ((Object o) -> true);

Why would I need to return a Predicate if I can return a result? A little enhanced version would be

interface PredicateOperation {
    boolean operation(String[] input);
}

and

PredicateOperation operation = (String[] input) -> true;

which still isn't particularly useful for Stream API since Stream#filter expects a java.util.function.Predicate<T>, not your type.

And, yes, stop using raw Predicates.