Java 8 Predicate

 Predicate

A Predicate interface represents a boolean-valued-function of an argument. This is mainly used to filter data from a Java Stream. The filter method of a stream accepts a predicate to filter the data and return a new stream satisfying the predicate. A predicate has a test() method which accepts an argument and returns a boolean value.

@Test
public void testPredicate(){
List<String> names = Arrays.asList("John", "Smith", "Samueal", "Catley", "Sie");
Predicate<String> nameStartsWithS = str -> str.startsWith("S");
names.stream().filter(nameStartsWithS).forEach(System.out::println);

In the above example, we have created a predicate which tests the names that start with S. This predicate is supplied to a stream.

Predicate also provides a few default and static method for composition and other purposes:

default Predicate<T> and(Predicate<? super T> other);
default Predicate<T> or(Predicate<? super T> other);
static <T> Predicate<T> isEquals(Object targetRef);
default Predicate<T> negate();

Following example demonstrates to use and method to compose predicates with multiple predicates.

@Test
public void testPredicateAndComposition(){
List<String> names = Arrays.asList("John", "Smith", "Samueal", "Catley", "Sie");
Predicate<String> startPredicate = str -> str.startsWith("S");
Predicate<String> lengthPredicate = str -> str.length() >= 5;
names.stream().filter(startPredicate.and(lengthPredicate)).forEach(System.out::println);
}

Comments

Post a Comment

Popular posts from this blog

Java 8 : Find the number starts with 1 from a list of integers

  List<Integer> list = List. of ( 12 , 32 , 14 , 15 , 56 ); //Result->12,14,15 List<String> listString = list.stream().map(String::valueOf).collect(Collectors.toList()); List<String> result1 = listString.stream().filter(x->x.startsWith( "1" )) .collect(Collectors.toList()); System. out .println( "result1-->" +result1); List<String> result2 = list.stream().map(x->x+ "" ).filter(x->x.startsWith( "1" )) .collect(Collectors.toList()); System. out .println( "result2-->" +result2);
Read more

Junit Mockito and Power Mockito

Mock vs Spy Both can be used to mock methods or fields. The difference is that  in mock, you are creating a complete mock or fake object while in spy, there is the real object and you just spying or stubbing specific methods of it . Mock vs InjectMock @Mock  creates a mock.  @InjectMocks  creates an instance of the class and injects the mocks that are created with the  @Mock  (or  @Spy ) annotations into this instance. Unit Testing Void Methods with Mockito and JUnit How to Test Void Methods  As we already know that our aim is to test void methods in a class. But it is also really important to understand why we test void methods.  Whenever we write unit test cases for any method, we expect a return value from the method. Generally, we use assert for checking if the method returns the value that we expect it to return, but in the case of void methods, they do not return any value. So how do we check if our method is functioning properly? Let’s...
Read more

Customized Immutable Class

Image
Java Immutable Class In Java, when we create an object of an immutable class, we cannot change its value. For example, String is an immutable class. Hence, we cannot change the content of a string once created. Besides, we can also create our own custom immutable classes. Here's what we need to do to create an immutable class. declare the class as final so it cannot be extended all class members should be private so they cannot be accessed outside of class shouldn't contain any setter methods to change the value of class members the getter method should return the copy of class members class members are only initialized using constructor. PROS - Immutable Object is Threadsafe. For Constant Value. Used as a HashMap Key. (String, Integer, all wrapper classes are immutable) Why Hashmap key should be immutable? Immutability allows you to get same hash code every time, for a key object. So it actually solves most of the problems in one go. Also, this class must honor the hashCode() ...
Read more