Java Java Data Structures Efficiency! Changing Course

can't find mistake

what am i doing wrong in fixVideoTitle()????

com/example/model/Course.java
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;
  }

}
com/example/model/Video.java
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;
  }

}
QuickFix.java
import com.example.model.Course;
import com.example.model.Video;

import java.util.Map;
import java.util.TreeMap;

public class QuickFix {

  public void addForgottenVideo(Course course) {
    // TODO(1):  Create a new video called "The Beginning Bits"
    Video video = new Video("The Beginning Bits");
    // TODO(2):  Add the newly created video to the course videos as the second video.
    course.getVideos().add(1,video);
  }

  public void fixVideoTitle(Course course, String oldTitle, String newTitle) {
    Map<String,Video> videosByTitle = videosByTitle(course);
    Video video = videosByTitle.get(oldTitle);
    video.setTitle(newTitle);
  }

  public Map<String, Video> videosByTitle(Course course) {
    Map<String,Video> videosByTitle= new TreeMap<>();
    for(Video video : course.getVideos()){
      Video videoByTitle = videosByTitle.get(video.getTitle());
      if(videoByTitle == null){
       videoByTitle = new Video(video.getTitle()); 
      }
      videosByTitle.put(video.getTitle(),videoByTitle);
    }
    return videosByTitle;
  }
}

1 Answer

andren
andren
28,384 Points

Your fixVideoTitle method is actually completely fine, the issue is in the videosByTitle method you wrote in task 2.

The videosByTitle method is supposed to generate a map where the keys are video titles and the value is the video itself, your code generates a map where the keys are the video titles but the value is a new video object, not the video object that actually came from the course object.

Since the video values are new objects, changing them will not affect the video object from the course object.

The videosByTitle method is actually meant to look like this:

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

You don't need to do any null checks or create any objects, just populate the map with the video title and object.

If you fix that function in your code like this:

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

import java.util.Map;
import java.util.TreeMap;

public class QuickFix {

  public void addForgottenVideo(Course course) {
    // TODO(1):  Create a new video called "The Beginning Bits"
    Video video = new Video("The Beginning Bits");
    // TODO(2):  Add the newly created video to the course videos as the second video.
    course.getVideos().add(1,video);
  }

  public void fixVideoTitle(Course course, String oldTitle, String newTitle) {
    Map<String,Video> videosByTitle = videosByTitle(course);
    Video video = videosByTitle.get(oldTitle);
    video.setTitle(newTitle);
  }

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

Then your code will work.

Thanx mate!!