mtumilowicz / java11-predicate

Java 11 Predicate Interface.

java11-predicate

The main goal of this project is to show updated Predicate Interface from Java 11.

overview

• and: returns a composed predicate that represents a short-circuiting logical AND of this predicate and another

  default Predicate<T> and(Predicate<? super T> other) {
      Objects.requireNonNull(other);
      return (t) -> test(t) && other.test(t);
  }    
  

• negate: returns a predicate that represents the logical negation of this predicate

  default Predicate<T> negate() {
          return (t) -> !test(t);
      }
  

• or: returns a composed predicate that represents a short-circuiting logical OR of this predicate and another

  default Predicate<T> or(Predicate<? super T> other) {
      Objects.requireNonNull(other);
      return (t) -> test(t) || other.test(t);
  }    
  

• isEqual: returns a predicate that tests if two arguments are equal according to Objects.equals(Object, Object)

  static <T> Predicate<T> isEqual(Object targetRef) {
      return (null == targetRef)
              ? Objects::isNull
              : object -> targetRef.equals(object);
  }    
  

• not: returns a predicate that is the negation of the supplied predicate

  static <T> Predicate<T> not(Predicate<? super T> target) {
      Objects.requireNonNull(target);
      return (Predicate<T>)target.negate();
  }    
  

best practices

Suppose that we want to filter Stream of objects by some field

class X {
    String value;
    
    // constructors, getters...
}

• naive approach

  List<X> filtered = xes.stream()
          .filter(x -> Objects.equals(x.value, "test"))
          .collect(Collectors.toList());
  

• better approach
  1. define static method in X

     static Predicate<X> byValue(String value) {
         return x -> nonNull(x) && Objects.equals(x.value, value);
     }    
     

  2. construct pipeline

     List<X> filtered = xes.stream()
             .filter(X.byValue("test1"))
             .collect(Collectors.toList());        
     

  3. easy to compose

     var filtered = xes.stream()
             .filter(X.byValue("test1").or(X.byValue("test2")))
             .collect(Collectors.toList());