Java Data Structures, Efficiency, Add Tags to course

Here is my answers for these 3 challenges:

   package com.example.model;

import java.util.List;
import java.util.ArrayList;
import java.util.Set;
import java.util.HashSet;


public class Course {
  private String mTitle;
  private Set<String> mTags;

  public Course(String title) {
    mTitle = title;
    mTags = new HashSet<String>();
    // TODO: initialize the set mTags
  }

  public void addTag(String tag) {
    // TODO: add the tag
    mTags.add(new String(tag));
  }

  public void addTags(List<String> tags) {
    // TODO: add all the tags passed in
    for (String allTags : tags){
      mTags.add(new String(allTags));
    }
  }

  public boolean hasTag(String tag) {
    // TODO: Return whether or not the tag has been added
    if (mTags.contains(tag)){
      return true;
    }
    return false;
  }

  public String getTitle() {
    return mTitle;
  }

}         

You can add to Sets using the Set.add instance method. Since you already have a set, mTags, this challenge task is asking you to add to the existing set.

Hope it helps!

Thanks for the help James! I'm coming to get you at number 1 soon!

Hello,

What you're wanting to do in the addTag function is just add the given tag to the set. Which you can then use this function on each item in the list passed into the addTags to add them to the set. Hopefully this will get you closer to solving the Challenge. If you have any further questions feel free to ask.

Per James' suggestion I tired:

  public void addTag(String tag) {
    // TODO: add the tag
    mTags.add(tag);
  }

  public void addTags(List<String> tags) {
    // TODO: add all the tags passed in
    for (String tag : tags)
      addTag(tag);
    }
  }

And got a Bummer! with syntax errors.

..per Craig's suggest of trying addAll, I tied:

  public void addTag(String tag) {
    // TODO: add the tag
    mTags.add(tag);
  }

  public void addTags(List<String> tags) {
    // TODO: add all the tags passed in
    mTags.addAll(tags);
  }

..and it finally passed (on part 2 of 3 at least).

By the way I got notion to try addAll from this page:

http://www.dotnetperls.com/hashset-java

with this code example:

import java.util.ArrayList;
import java.util.HashSet;

public class Program {
    public static void main(String[] args) {

    // An ArrayList of three Strings.
    ArrayList<String> list = new ArrayList<>();
    list.add("socrates");
    list.add("plato");
    list.add("cebes");

    // Add all elements to HashSet.
    HashSet<String> hash = new HashSet<>();
    hash.addAll(list);

    // Use contains.
    boolean a = hash.contains("cebes");
    System.out.println(a);

    // Use containsAll.
    boolean b = hash.containsAll(list);
    System.out.println(b);
    }
}

Thanks to James and Craig for all their help.

I got my 390 points for the full course, which puts me at 56,000 points overall:

http://teamtreehouse.com/jameswhite7

..and am sorta near the top of the Treehouse's all time Points Leaderboard once again:

http://teamtreehouse.com/leaderboards

Oh..and what about part 3 of 3 for the challenge?

.

Luckily (and as Louis Pasteur said "Fortune favors the prepared mind")

now that I've spend days and days researching HashSets,

I knew that there is a HashSet.contains method:

http://www.tutorialspoint.com/java/util/hashset_contains.htm

Here's the sample code from that page:

import java.util.*;

public class HashSetDemo {
   public static void main(String args[]) {
      // create hash set
      HashSet <String> newset = new HashSet <String>();

      // populate hash set
      newset.add("Learning"); 
      newset.add("Easy");
      newset.add("Simply");  

      // check the existence of element
      boolean exist=newset.contains("Simply");

      System.out.println("Is the element 'Simply' exists: "+ exist);
   }    
}

So I figured..let's use that example's boolean line slightly modified:

  public boolean hasTag(String tag) {
    // TODO: Return whether or not the tag has been added
    boolean exists=mTags.contains(tag);
    return exists;
  }

Can you guess what happened?

By the way - the java code in neither the 'Song.java' or 'SongBook.java' (from the 'S4V6' folder of the zip download for the course) has (or uses) any example of hashset.contains...

I guess now I'll go back to "meditating upon" the Tacocat challenge.

The final (ridiculously involved) challenge for the latest Python Flask Social Network course:

http://teamtreehouse.com/library/build-a-social-network-with-flask

Hi James,

Thanks for the info,

but it is in trying to figure out the code for

use this function on each item in the list passed into the addTags

..that has me stuck.

Exactly HOW do I use such a function?

Thanks in advance for any code hints you can provide.

Hi James,

Thanks for the additional guidance,

but my brain is fried in just completing the last challenge of the Java Data Structures course using this forum thread:

https://teamtreehouse.com/forum/bummer-are-you-sure-you-updated-the-videos-title

I'm going to lie down a while and let the smoke stop coming out of my ears..and work on the addTags challenge a little latter..

I think I'm getting closer, but I keep getting:

Bummer! There is a compiler error. Please click on preview to view your syntax errors!

..and the preview window is totally blank!

Here's the code I'm working with now for 'addTag':

  public void addTag(String tag) {
    // TODO: add the tag
    mTags.add(tag);
  }

I still think it's not passing, though, because of my 'addTags' code.

I wish the two "fixes" of part 2 of the challenge had been split!

Anyway, here's some of the code I've tried:

Try#1:

  public void addTags(List<String> tags) {
    // TODO: add all the tags passed in
    for (String tag : tags)
      addTag(tag);
    }
  }

Try#2:

  public void addTags(List<String> tags) {
    // TODO: add all the tags passed in
    for (String mTags : tags)
     //here's a real shot in the dark - using .addall
      mTags.addall(tags);
    }
  }

Try#3:

  public void addTags(List<String> tags) {
    // TODO: add all the tags passed in
    for (String mTags : tags)
      mTags.add(mTag.add(tags));
    }
  } 

Try#4:

  public void addTags(List<String> tags) {
    // TODO: add all the tags passed in
    for (String mTags : tags)
      addTag(mTags);
    }
  } 

Try#5:

  public void addTags(List<String> tags) {
    // TODO: add all the tags passed in
    for (String name : tags)
      addTag(name);
    }
  } 

Try#6:

  public void addTags(List<String> tags) {
    // TODO: add all the tags passed in
    for (String mTags : tags)
      mTags.add(tags);
    }
  } 

I don't know what else to try..

Is List<String> some kind of weird generic?

http://docs.oracle.com/javase/tutorial/extra/generics/subtype.html

Hi James,

Why is this a shot in the dark?

//here's a real shot in the dark - using .addall

It's addAll (note the case). You shouldn't need the for loop. It takes a collection as a parameter, so just push in tags.

I think I fixed the problem so you should start seeing the compiler errors on this challenge.

Hope it helps.

Hi James and all,

I would not have gotten through this challenge without your help. Even though these posts are now a couple weeks old, for what it's worth, I just passed Part 3 using the .contains() method with an if statement.

This was a fun challenge. I find that my problem most of the time is over thinking what the challenge is asking me to do.

Everyone struggling on this challenge should take a look at Sets.

Even though I am giving you the specific times of the Sets video, its a good idea to watch the FULL video. Even though the video was relatively recent, it never hurts to try and catch something you may have missed.

Challenge 1 is covered at 1:43

Challenge 2 is covered at 2:05. (This is a 2 part challenge, the // TODO gives you the a REALLY good hint on what to do.)

public void addTag(String tag) {
    // TODO: ADD the tag
  }

  public void addTags(List<String> tags) {
    // TODO: ADD ALL the tags passed in
  }

Challenge 3 I had to do some critical thinking. A small hint, the TODO is asking you if a tag has been added or not, or better yet if the tag is CONTAINED in the mTags HashSet<>();. Using an if statement here is what I did.

public boolean hasTag(String tag) {
    // TODO: Return whether or not the tag has been added
    return false;
  }

1. Remember your syntax.
2. Remember to check your IMPORTS!
3. Remember to check your variable names.

Finally, everything you need to complete these challenges has been presented to you. While outside resources are always great to read up on, the instructors at Treehouse will not let you down or set you up for failure.

Good luck, have fun, and happy coding!

I like going thru the videos... but the challenges are really putting me off. Guess I am still to new to programming to be able to put all these different ideas from previous lessons together yet.

Ok so I got the the point where I read this whole thread and I am more confused than before. I followed Brody Ricketts advice but I am stuck on 3/3;

The error: "I called hasTag with "karaoke" and got back false, expected true"

The code:

public void addTags(List<String> tags) {
    // TODO: add all the tags passed in
    for (String allTags : tags){
      mTags.add(new String(allTags));
    }
  }

What to do? Can someone clarify it or lend me a hand where should I read more about it?