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Java Java Data Structures - Retired Efficiency! Changing Course

Prasoon Shukla
Prasoon Shukla
3,426 Points
Posted by Prasoon Shukla
Prasoon Shukla
3,426 Points

Efficiency challenge 3 of 3

I saw this code as solution for this excercise in a discussion. It is working too. But not able to understand, when we use vbt.remove(oldTitle); it should return a map. Why is the value set to Video when Video is not a map? How does .remove work in a map? Does it removes key as well as value for the key? If yes, we should have got a map when we remove a key from the map and not another class (Video in this case).

public void fixVideoTitle(Course course, String oldTitle, String newTitle) {

   Map<String, Video> vbt = videosByTitle(course);

   Video vid = vbt.remove(oldTitle);

   vid.setTitle(newTitle);

   vbt.put(newTitle, vid);

1 Answer

Chris Freeman
MOD
Chris Freeman
Treehouse Moderator 68,441 Points
Chris Freeman
Chris Freeman
Treehouse Moderator 68,441 Points

While it operates on a Map, the .removed method returns the V value found at the key oldTitle

The issue with this solution is that it removes the entry from the map. So while the title is changed, it is no longer in the map. A better choice would be to use the .get() method which leaves the Map intact:

    Video vid = vbt.get(oldTitle);
Prasoon Shukla
Prasoon Shukla
3,426 Points
Prasoon Shukla
Prasoon Shukla
3,426 Points

Thanks Chris. So if after 

Video vid = vbt.get(oldTitle);

// following is done:
vid.setTitle(newTitle);

will the old title be automatically replaced by new title?

[MOD: added ```java formatting -cf]

Chris Freeman
Chris Freeman
Treehouse Moderator 68,441 Points
Chris Freeman
Chris Freeman
Treehouse Moderator 68,441 Points

Correct. More than automatically, I'd say explicitly set. vbt.get() returns a pointer to the Map entry. vid holds that pointer. So the setTitle is the Map entry method that operates on that Map entry.