Find value and set value from two list-CodePudding

I have a list of

List<User> userList =  ...

List<Long> UserIdWithBilling = .....

I search to set a field of User to true if the value in the list of UserIdWithBilling are found in the userList id field

 for(Long userId : UserIdWithBilling){
     Optional<User> optUserList =  userList.stream()
                                           .filter(ul->ul.getUserId().longValue()==userId)
                                           .findFirst();
        
     if(optUserList.isPresent()){
            optUserList.get().setBilling(true);
     }
        
 }

that work but is there a way clean, faster

Maybe there is a way to do in via one line

CodePudding user response：

Convert UserIdWithBilling to a set, then use contains in the filter.

Set<Long> ids = new HashSet<>(UserIdWithBilling);
userList.stream()
   .filter(x -> ids.contains(x.getUserId()))
   .forEach(x -> x.setBilling(true));

CodePudding user response：

Here is the executable test with the old and new solution (as a one-liner)

import org.junit.jupiter.api.BeforeAll;
import org.junit.jupiter.api.Test;
import org.junit.jupiter.api.TestInstance;

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

import static org.junit.jupiter.api.Assertions.assertFalse;
import static org.junit.jupiter.api.Assertions.assertTrue;

@TestInstance(TestInstance.Lifecycle.PER_CLASS)
public class UserList {
    List<User> userList =  new ArrayList<User>();
    List<Long> userIdsWithBilling = new ArrayList<>();

    @BeforeAll
    public void setup() {
        for (long id=1l; id<=10l; id  ) userList.add(new User(id, false));
        for (long id=1l; id<=5l; id  ) userIdsWithBilling.add(id);
    }

    @Test
    public void oldSolution() {
        for (Long userId : userIdsWithBilling) {
            Optional<User> optUserList = userList.stream()
                    .filter(ul -> ul.getId().longValue() == userId)
                    .findFirst();

            if (optUserList.isPresent()) {
                optUserList.get().setBilling(true);
            }
        }
        for (int i=0; i<5; i  ) assertTrue(userList.get(i).getBilling());
        for (int i=5; i<10; i  ) assertFalse(userList.get(i).getBilling());
    }

    @Test
    public void newSolution() {
        userList.stream().filter(user -> userIdsWithBilling.contains(user.getId()))
                .forEach(user -> user.setBilling(true));

        for (int i=0; i<5; i  ) assertTrue(userList.get(i).getBilling());
        for (int i=5; i<10; i  ) assertFalse(userList.get(i).getBilling());
    }

    private static class User {
        private Long id;
        private Boolean billing = false;

        public User(long id, boolean billing) {
            this.id = id;
            this.billing = billing;
        }
        public Long getId() {
            return id;
        }
        public void setId(Long id) {
            this.id = id;
        }
        public void setBilling(Boolean billing){
            this.billing = billing;
        }
        public Boolean getBilling(){
            return billing;
        }
    }
}

For large lists you can use parallel streams but please read the docs on that.

CodePudding user response：

On one line, but keep in mind it changes the billing to true on the original userList. You have to rewrite if you want a new list like in your question.

UserIdWithBilling.forEach(
        billedUser -> userList.stream().filter(u -> u.getUserId() == billedUser).toList()
            .forEach(u -> u.setBilling(true)));