Java Language Filter

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Example

filter() is used to indicate that you would like the value only if it matches your predicate.

Think of it like if (!somePredicate(x)) { x = null; }.

Code examples:

String value = null;
Optional.ofNullable(value) // nothing
        .filter(x -> x.equals("cool string"))// this is never run since value is null
        .isPresent(); // false
String value = "cool string";
Optional.ofNullable(value) // something
        .filter(x -> x.equals("cool string"))// this is run and passes
        .isPresent(); // true
String value = "hot string";
Optional.ofNullable(value) // something
        .filter(x -> x.equals("cool string"))// this is run and fails
        .isPresent(); // false
FlatMap