A
Functional Interface is an Interface which allows only one Abstract method within the Interface scope. There are some predefined functional interface in Java like Predicate, consumer, supplier etc. The return type of a Lambda function (introduced in JDK 1.8) is a also functional interface.
The Functional Interface
PREDICATE is defined in the
java.util.function package. It improves manageability of code, helps in unit-testing them separately, and contain some methods like:
- isEqual(Object targetRef) : Returns a predicate that tests if two arguments are equal according to Objects.equals(Object, Object).
static Predicate isEqual(Object targetRef)
Returns a predicate that tests if two arguments are
equal according to Objects.equals(Object, Object).
T : the type of arguments to the predicate
Parameters:
targetRef : the object reference with which to
compare for equality, which may be null
Returns: a predicate that tests if two arguments
are equal according to Objects.equals(Object, Object)
- and(Predicate other) : Returns a composed predicate that represents a short-circuiting logical AND of this predicate and another.
default Predicate and(Predicate other)
Returns a composed predicate that represents a
short-circuiting logical AND of this predicate and another.
Parameters:
other: a predicate that will be logically-ANDed with this predicate
Returns : a composed predicate that represents the short-circuiting
logical AND of this predicate and the other predicate
Throws: NullPointerException - if other is null
- negate() : Returns a predicate that represents the logical negation of this predicate.
default Predicate negate()
Returns:a predicate that represents the logical
negation of this predicate
- or(Predicate other) : Returns a composed predicate that represents a short-circuiting logical OR of this predicate and another.
default Predicate or(Predicate other)
Parameters:
other : a predicate that will be logically-ORed with this predicate
Returns:
a composed predicate that represents the short-circuiting
logical OR of this predicate and the other predicate
Throws : NullPointerException - if other is null
- test(T t) : Evaluates this predicate on the given argument.boolean test(T t)
test(T t)
Parameters:
t - the input argument
Returns:
true if the input argument matches the predicate, otherwise false
Examples
Example 1: Simple Predicate
Output:
True
Example 2: Predicate Chaining
Output:
True
False
Example 3: Predicate in to Function
Output:
Number 10
Example 4: Predicate OR
Output:
True
Example 5: Predicate AND
Output:
False
True
Example 6: Predicate negate()
Output:
False
Example 7: Predicate in Collection
Output:
[User Name : John, Role :admin]
The same functionality can also be achieved by using
Stream API
and
lambda functions offered since JDK 1.8 on top of the Collections API.
The
Stream API allows "streaming" of collections for dynamic processing. Streams allow concurrent and parallel computation on data (using internal iterations), to support database-like operations such as grouping and filtering the data (similar to GROUP BY and WHERE clause in SQL). This allows the developers to focus on "what data is needed" instead of "how data is needed" since streaming hides the details of the implementation and provides the result. This is done by providing predicates as inputs to functions operating at runtime upon the streams of collections. In the following example, we illustrate how Stream API can be used along with predicates to filter the collections of data as achieved in Example 7.
