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Java 8 Streams - Stream.filter Examples

Java 8 Streams Java Java API 

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Interface:

java.util.stream.Stream

java.lang.AutoCloseableAutoCloseablejava.util.stream.BaseStreamBaseStreamjava.util.stream.StreamStreamLogicBig

Method:

Stream<T> filter(Predicate<? super T> predicate)

Returns a stream consisting of the elements of this stream that match the given predicate.


Examples


package com.logicbig.example.stream;

import java.util.stream.Stream;

public class FilterExample {

    public static void main(String... args) {
        Stream<String> s = Stream.of("one", "two", "three", "four");
        Stream<String> s2 = s.filter(e -> e.endsWith("e"));
        s2.forEach(System.out::println);
    }
}

Output

one
three




    @Override
    public User loginUser (User user) {
        Optional<User> loggedInUser = users.stream()
                                           .filter(u -> validateUser(u, user))
                                           .findAny();
        return loggedInUser.isPresent() ? loggedInUser.get() : null;
    }

    private static boolean validateUser (User existingUser, User user) {
        return existingUser.getEmailAddress()
                           .equals(user.getEmailAddress())
                            && existingUser.getPassword()
                                           .equals(user.getPassword());
    }
Original Post




This example shows that updating an external variable from behavioral parameter can lead to non-determinist result. 

package com.logicbig.example;


import java.util.stream.IntStream;

public class StatefulExample2 {
    private static int count = 0;

    public static void main (String[] args) {
        for (int i = 0; i < 5; i++) {
            process();
        }
    }

    private static void process () {
        count = 0;

        IntStream stream = IntStream.range(1, 1000);
        //finding the sum of even numbers
        int sum = stream.parallel()
                        .filter(i -> {
                            boolean b = i % 2 == 0;
                            if (b) {
                                count++;//updating count hence making it stateful.
                            }
                            return b;
                        })
                        .sum();

        System.out.printf("sum :%d  count:%d%n", sum, count);
    }
}

Output

sum :249500  count:399
sum :249500  count:411
sum :249500  count:456
sum :249500  count:456
sum :249500  count:456
Original Post




This example shows alternative way to do the same thing as above example but in a stateless manner. 

package com.logicbig.example;

import java.util.stream.IntStream;


public class StatefulFixExample2 {
    public static void main (String[] args) {
        for (int i = 0; i < 5; i++) {
            process();
        }
    }

    private static void process () {
        IntStream stream = IntStream.range(1, 1000);

        //finding the even numbers
        int[] even = stream.parallel()
                           .filter(i -> i % 2 == 0)
                           .toArray();

        //finding sum
        int sum = IntStream.of(even).parallel().sum();

        System.out.printf("sum :%d  count:%d%n", sum, even.length);
    }
}

Output

sum :249500  count:499
sum :249500  count:499
sum :249500  count:499
sum :249500  count:499
sum :249500  count:499
Original Post

See Also