StreamPlayground.java

package streams;

import static org.junit.jupiter.api.Assertions.assertEquals;

import java.util.ArrayList;
import java.util.List;
import java.util.Optional;
import java.util.stream.Collectors;

import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;

class StreamPlayground {

    private class User {
        String username;
        boolean active;
        Address address;

        public User(String username, boolean active, Address address) {
            this.username = username;
            this.active = active;
            this.address = address;
        }
    }

    private class Address {
        String state;
        String street;

        public Address(String state, String street) {
            this.state = state;
            this.street = street;
        }
    }

    private List<User> users = new ArrayList<>();

    @BeforeEach
    void beforeEach() {
        users.clear(); // Clear the list before each test
        users.add(new User("User1", true, new Address("California", "123 Main St")));
        users.add(new User("User2", false, new Address("New York", "456 Broadway")));
        users.add(new User("User3", true, new Address("Texas", "789 Houston Ave")));
        users.add(new User("User4", false, new Address("Florida", "321 Miami Blvd")));
        users.add(new User("User5", true, new Address("Illinois", "654 Chicago Rd")));
        users.add(new User("User6", false, new Address("Washington", "888 Seattle Way")));
        users.add(new User("User7", true, new Address("Oregon", "999 Portland Ave")));
        users.add(new User("User8", false, new Address("Nevada", "111 Las Vegas Blvd")));
        users.add(new User("User9", true, new Address("Arizona", "222 Phoenix St")));
        users.add(new User("User10", false, new Address("Michigan", "333 Detroit Ave")));
    }


    // class Streem {  

    //     Listt list;

    //     public Streem(Listt list){
    //         this.list = list;
    //     }

    //     public filter()

    // }

    // class Listt {

    //     String[] firstNames;

    //     Streem stream(){
    //         return new Streem(this);
    //     }

    // }




    @Test
    void activeUsersInTexasTest(){

        long count = 0;
        count = users.stream()
            .filter(user -> user.address.state.equals("Texas") && user.active)
            //no more stream ops, terminate
            .count();
            //count = list.size 

        assertEquals(1l, count);

         // 1. Call stream() on any collection object to get reference to Stream class
        // 2. Perform functional operations like map, filter, min, max, etc
        // 3. Perform terminating operation
    }

    @Test
    void streamDemo() {

        // Imperative
        List<String> usernames = new ArrayList<>();
        for(int i = 0; i<users.size(); i++){
            usernames.add(users.get(i).username);
        }

        // Functional 
        usernames = users.stream() // stream of 10 users
            // for each user, return me just the username
            .map(user -> user.username)
            // I want to only keep the usernames that are less the 10 characters in length
            .filter(username -> username.length() < 10)
            .collect(Collectors.toList());


        // Functional 
        Optional<String> firstUsernameLessThan10Chars = users.stream() // stream of 10 users
            // for each user, return me just the username
            .map(user -> user.username)
            // I want to only keep the usernames that are less the 10 characters in length
            .filter(username -> username.length() < 10)
            .findFirst();

        if(firstUsernameLessThan10Chars.isPresent()){
            System.out.println("present");
        }else{
            throw new RuntimeException("error");
        }

        // 1. Call stream() on any collection object to get reference to Stream class
        // 2. Perform functional operations like map, filter, min, max, etc
        // 3. Perform terminating operation
    }

}