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Predicate

layout: default title: Predicate<T> Functional Interface

Java 8 provides a number of functional interfaces as part of the java.util.function package.

One interface is Predicate<T>, named for the mathematical concept of a function that returns a boolean value. * It is generic, so we tell it what kind of object to test. * Its one method takes the parameterized type as an argument, and returns a boolean.

@FunctionalInterface
public interface Predicate <T> {
  public boolean test(T t);
}

Drill

Lambdas/com.example.lambdas.drills.UsingPredicate * Declare and define a Predicate that tests whether an input String ends with "!!" * Declare and define a Predicate that tests whether an input String is all uppercase. * Test your two Predicates by calling their test methods with some Strings.


Drill

Lambdas/com.example.lambdas.drills.PlanetUtilities

  • Refactor your filterPlanets method to take a Predicate<Planet> instead of a PlanetTester.
  • The body of filterPlanets will not change because Predicate and PlanetTester both have the method boolean test(Planet).

Lambdas/com.example.lambdas.drills.FilterPlanets

  • Run FilterPlanets again.
  • Notice that your FilterPlanets class is unchanged because the lambda expression is based on the function descriptor (parameter and return types) rather than on names.

(Solution: PlanetUtilities2.java, FilterPlanets2.java)

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