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Java Introduction to Functional Programming Reduction and Aggregation Reduce Housing Records

Nancy Melucci
PLUS
Nancy Melucci
Courses Plus Student 35,157 Points
Posted by Nancy Melucci
Nancy Melucci
Courses Plus Student 35,157 Points

Need more feedback than test is providing on OptionalInt return

I am just coming back to this tutorial and challenge after 4 months. I can't make heads or tails of what is wrong with my code though, and the tests advice to "compare to the imperative" really isn't helping me figure out how to change my code. The pre-written part of the methods returns OptionalInt.empty() and I have no clue what to replace it with. Thanks for any help you can give.

package com.teamtreehouse.challenges.homes;

import com.teamtreehouse.challenges.homes.model.HousingRecord;
import com.teamtreehouse.challenges.homes.service.HousingRecordService;

import java.util.Comparator;
import java.util.List;
import java.util.Optional;
import java.util.OptionalInt;

public class Main {
  public static void main(String[] args) {
    HousingRecordService service = new HousingRecordService();
    List<HousingRecord> records = service.getAllHousingRecords();
    System.out.printf("There are %d housing records. %n %n", records.size());

    System.out.println("Lowest home value index:");
    int lowest = getLowestHomeValueIndexImperatively(records);
    System.out.println("Imperatively:  " + lowest);
    OptionalInt lowestDeclaratively = getLowestHomeValueIndexDeclaratively(records);
    System.out.println("Declaratively:  " + lowestDeclaratively);

    System.out.printf("%n%nHighest housing record based on current value index:%n");
    HousingRecord record = getHighestValueIndexHousingRecordImperatively(records);
    System.out.println("Imperatively:  " + record);
    Optional<HousingRecord> recordDeclaratively = getHighestValueIndexHousingRecordDeclaratively(records);
    System.out.println("Declaratively:  " + recordDeclaratively);
  }

  public static int getLowestHomeValueIndexImperatively(List<HousingRecord> records) {
    int lowest = -1;
    for (HousingRecord record : records) {
      int index = record.getCurrentHomeValueIndex();
      if (lowest == -1) {
        lowest = index;
      } else {
        if (index < lowest) {
          lowest = index;
        }
      }
    }
    return lowest;
  }

  public static OptionalInt getLowestHomeValueIndexDeclaratively(List<HousingRecord> records) {
    // TODO: Create a stream off the records
    // TODO: Map the stream to an IntStream on `HousingRecord.getCurrentHomeValueIndex` to expose new methods
    // TODO: Return the minimum value from the stream.  It should be an optional because records could be empty.
    System.out.println(records.stream()
      .map(HousingRecord::getCurrentHomeValueIndex)
      .min(Comparator.comparingInt(Integer::intValue))
    );
    return OptionalInt.empty();
  }

  public static HousingRecord getHighestValueIndexHousingRecordImperatively(List<HousingRecord> records) {
    HousingRecord maxRecord = null;
    for (HousingRecord record : records) {
      if (maxRecord == null) {
        maxRecord = record;
      } else {
        if (record.getCurrentHomeValueIndex() > maxRecord.getCurrentHomeValueIndex()) {
          maxRecord = record;
        }
      }
    }
    return maxRecord;
  }

  public static Optional<HousingRecord> getHighestValueIndexHousingRecordDeclaratively(List<HousingRecord> records) {
    // TODO: Create a stream off of the records
    // TODO: Find and return the maximum using a Comparator that compares the current home value index
    System.out.println(records.stream()
      .map(HousingRecord::getCurrentHomeValueIndex)
      .max(Comparator.comparingInt(Integer::intValue))
    );
    return Optional.empty();
  }
}
Nancy Melucci
Nancy Melucci
Courses Plus Student 35,157 Points
Nancy Melucci
Nancy Melucci
Courses Plus Student 35,157 Points

I figured it out.

  public static OptionalInt getLowestHomeValueIndexDeclaratively(List<HousingRecord> records) {
    // TODO: Create a stream off the records
    // TODO: Map the stream to an IntStream on `HousingRecord.getCurrentHomeValueIndex` to expose new methods
    // TODO: Return the minimum value from the stream.  It should be an optional because records could be empty
    Integer lowestDeclaratively = records.stream()
      .map(HousingRecord::getCurrentHomeValueIndex)
      .min(Comparator.comparingInt(Integer::intValue))
      .orElse(0);

     return OptionalInt.of(lowestDeclaratively);
  }

  public static OptionalInt getHighestValueIndexHousingRecordDeclaratively(List<HousingRecord> records) {
    // TODO: Create a stream off of the records
    // TODO: Find and return the maximum using a Comparator that compares the current home value index
    Integer recordDeclaratively = records.stream()
      .map(HousingRecord::getCurrentHomeValueIndex)
      .max(Comparator.comparingInt(Integer::intValue))
      .orElse(0);

    return OptionalInt.of(recordDeclaratively);
  }

1 Answer

James Sawkins
James Sawkins
4,914 Points
James Sawkins
James Sawkins
4,914 Points

Think you have made it more complicated then it needed to be, you just need to compare the records

public static Optional<HousingRecord> getHighestValueIndexHousingRecordDeclaratively(List<HousingRecord> records) {
    // TODO: Create a stream off of the records
    return records.stream()
    // TODO: Find and return the maximum using a Comparator that compares the current home value index
        .max(Comparator.comparingInt(HousingRecord::getCurrentHomeValueIndex));
  }