Java8 FunctionalInterface

Question

public static <E extends Enum<E>> boolean validateEnum(Class<E> clazz, String s) {
    return EnumSet.allOf(clazz).stream().anyMatch(e -> e.name().equals(s));
}

Following is an example invocation of the above method

boolean isValid = validateEnum(Animal.class, "DOG");
boolean isValid = validateEnum(Color.class, "Red");

Can this same functionality be implemented using a Java 8 FunctionalInterface. I have tried creating a BiPredicate but am getting compiler errors when I try this.

final BiPredicate<String,Class> biPre = (string1, clazz) -> EnumSet.allOf(clazz).stream().anyMatch(e -> e.name().equals(s));

final BiPredicate<String,Class> biPre to final BiPredicate<String,Class<Animal>> biPre ? — soorapadman
– soorapadman, Commented Jan 22, 2019 at 4:17
Thats not generic. If I need to implement a validateEnum for another Enum I will need to create a new BiPredicate — ArunM
– ArunM, Commented Jan 22, 2019 at 4:24

Ravindra Ranwala · Accepted Answer · 2019-01-22 14:17:43Z

6

Here's a one way of doing it,

final BiPredicate<String, ? super Enum<?>> biPre = (string1, enumType) -> EnumSet
        .allOf(enumType.getDeclaringClass()).stream().anyMatch(e -> e.name().equals(string1));

And here's the client code,

boolean test = biPre.test("DOG", Animal.CAT);

However passing an enum constant instead of a class literal seems a bit awkward here.

If you really need to use the type token here's what you should do,

final BiPredicate<String, Class<? extends Enum<?>>> biPre = (string1, clazz) -> Arrays
    .stream(clazz.getEnumConstants()).anyMatch(e -> e.name().equals(string1));

The client now looks like this,

boolean test = biPre.test("DOG", Animal.class);

edited Jan 22, 2019 at 14:17

answered Jan 22, 2019 at 4:55

Ravindra Ranwala

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Pankaj Singhal · Accepted Answer · 2019-01-22 05:02:46Z

2

You have to declare the class in which the biPre is defined as generic similar to the function validateEnum.

public class Test<E extends Enum<E>> {
    BiPredicate<String,Class<E>> biPre = (string1,clazz) -> EnumSet.allOf(clazz).stream().anyMatch(e -> e.name().equals(string1));
}

Then you can test it like this:

boolean isValid = biPre.test( "DOG", (Class<E>) Animal.class);

answered Jan 22, 2019 at 5:02

Pankaj Singhal

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