Where did I go wrong here? :/

Question

I've tried this a couple ways already. What am I missing?

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;
    for (Course video : videos)  {
     videosByTitle.add(video.getVideo());

    }
  }

  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;

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) {

  }

  public Map<String, Video> videosByTitle(Course course) {
    return null;
  }

}

Answer 1 · 2017-11-16T15:50:25Z

November 16, 2017 3:50pm

OK, so let's take this one step at a time :-)

What you want to return with this method is a Map. A Map has combinations of key and value, and you use the key to to find the value. Here the key is the video title (String) and the value is the video object itself (Video). The idea is that once we have this map, all we need to remember is the video title. Then we can just type:

Video javaBasicsVideo = videosMap.get("Java Basics");

This will create a reference to the Video object with the title "JavaBasics". That's very handy, and that's why we want to have this method.

So how do we do this?

Create an empty map that takes a String and a Video
Get the list of all course videos
Loop through all the videos in the list, put each video in the map
return the map

So first we create an empty map:

Map<String, Video> videosMap = new HashMap<>();

This creates an empty map. It takes a String as a key (that's the video title) and a Video as the value. But it's still empty. We need to put all the course videos inside it. We can add things to the map like that (just an example):

videosMap.put("Java Basics", javaBasicsVideo);
//javaBasicsVideo is a variable of the type Video

So we need to do something like this, but for each video in the course. How do we know which videos are in the course? Like this other person told you, there's a getter method that you can use to get all the videos in a course. Look in the Course class, it's called getVideos(). So we'll just use that:

List<Video> allVideosInTheCourse = course.getVideos();

OK, so we have all the videos in a list. Now you can use a for each loop to go through each element in that list. For each video, just put the video title and the video itself in the map you created before.

Once you're done adding all the videos to the map, after the loop, just return the map:

return videosMap;

Try putting all those steps together, and add another comment here if it's still not clear.

Answer 2 · 2017-11-16T19:49:26Z

November 16, 2017 7:49pm

The error you have happens because the HashMap class needs to be imported. Add this line:

import java.util.HashMap;

Then the method:

public Map<String, Video> videosByTitle(Course course) { 
Map<String, Video> videosMap = new HashMap<>(); 
videosMap.put();  //remove this line
List<Video> allVideosInTheCourse = course.getVideos(); 
for ( Video video : Course); //You're on the right track, but this line won't work. 
return videosMap; 
}

This pretty important, because for and for-each loops are everywhere! This is what a for each loop should look like (imagine nameList is a list of names):

for(String name : nameList) {
    //do something with text
}

The second part of the for each loop, after the colon, has to be an iterable (for example Array, List, Set, are all iterables). So you can't just use the course there, instead you need to loop through the list you just created 'allVideosInTheCourse'.
After the brackets, instead of a semicolon, you need curly braces. All the code you put inside the curly braces happens for each element in the list.

For example:

for(String name : nameList) {
    System.out.println(name);
}

This will print each name in the nameList on a separate line.

You need to do the same thing, but instead of printing the videos, you want to put them in the map. Try it again! Don't worry about being "slow". This stuff is difficult, but with more practice it will sink in, I promise.

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Where did I go wrong here? :/

Livia Galeazzi

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2 Answers

Livia Galeazzi

Livia Galeazzi

annapoff

annapoff

Livia Galeazzi

Livia Galeazzi