Welcome to the Treehouse Community

Want to collaborate on code errors? Have bugs you need feedback on? Looking for an extra set of eyes on your latest project? Get support with fellow developers, designers, and programmers of all backgrounds and skill levels here with the Treehouse Community! While you're at it, check out some resources Treehouse students have shared here.

Looking to learn something new?

Treehouse offers a seven day free trial for new students. Get access to thousands of hours of content and join thousands of Treehouse students and alumni in the community today.

Start your free trial

Java Java Data Structures Efficiency! Changing Course

I cnt pass this challenge

We cn use replace method

package com.example.model;

import java.util.List;

public class Course {
  private String mName;
  private List<Video> mVideos; 

  public Course(String name, List<Video> videos) {
    mName = name;
    mVideos = videos;

  public String getName() {
    return mName;

  public List<Video> getVideos() {
    return mVideos;

package com.example.model;

public class Video {
  private String mTitle;

  public Video(String title) {
    mTitle = title;

  public String getTitle() {
    return mTitle;

  public void setTitle(String title) {
    mTitle = title;

import com.example.model.Course;
import com.example.model.Video;

import java.util.Map;
import java.util.*;

public class QuickFix {

  public void addForgottenVideo(Course course) {
    List<Video> videoList = course.getVideos();
    Video video = new Video("The Beginning Bits");
    videoList.add(1, video);

    // TODO(1):  Create a new video called "The Beginning Bits"

    // TODO(2):  Add the newly created video to the course videos as the second video.


  public void fixVideoTitle(Course course, String oldTitle, String newTitle) {
      Map<String, video> newVideoMap = new TreeMap<>(course);
      newVideoMap.replace(video.getTitle() oldTitle, newTitle);  

  public Map<String, Video> videosByTitle(Course course) {
    List<Video> videoList = course.getVideos();
    Map<String, Video> videoMap = new TreeMap<>();
    for(Video video : videoList) {
    videoMap.put(video.getTitle(), video);
   return videoMap;


1 Answer

What you're doing is you're creating a new map of videos, and you try to replace the oldTitle by the newTitle in that map. What you should do is change the title in the correct Video object using its setTitle(String title) method. First retrieve the correct Video object using the map returned by the "findVideoByTitle" method. Then use the setTitle method to change the title of the Video object.