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Java Java Data Structures Efficiency! Add tags to a course

Kevin Lankford
Kevin Lankford
1,983 Points

Having trouble initializing mTags. Am I not adding the arguments correctly?

I'm getting an error thats saying there aren't the correct amount of arguments in the constructor. My idea of setting the constructor was to initialize the variables within the class. Am I not getting the concept of the task? Any help is appreciated, thank you.

com/example/model/Course.java
package com.example.model;

import java.util.List;
import java.util.Set;

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

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

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

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

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

  public String getTitle() {
    return mTitle;
  }

}

1 Answer

Hi Kevin,

To initialise the mTags variable, you need to assign a new instance of HashSet to it. You don't need to change the parameters that the constructor takes. Something like:

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

Make sure you also import the HashSet at the top of the code.

I hope that helps,

Steve.

Kevin Lankford
Kevin Lankford
1,983 Points

Thank you! So in this perspective, am I establishing that I am using a collection of type Set when initializing in the class "Set<String> mTags;" and then specifying when I get into the constructor that I will be using a HashSet "mTags = new HashSet<String>();?

Hi Kevin,

The class definition has a space for its own content, so the template for each instance contains a memory space for the member variables. But this is just so the application can assess the overhead required for each created instance. If you never create an instance, the compiler will allocate no memory for the class.

The constructor, in this example, initialises the mTags variable, because that's the task this challenge wants you to complete. So, the memory overhead (hole) has been created because the compiler knows what an instance of each class needs. Then, the constructor here has created an mTags instance of Set and assigned that to the memory hole.

You are then free to use the Set as you wish.

Creating the declaration in the class definition isn't the same as initialising it. The member variables are declared in the class. In this case, you initialise the mTitle with a value by passing a value into the constructor. The mTags member variable is initialised with a blank instance of HashSet, ready to be used later. The memory management of that occurs outside of the Course class.

I hope that made some sense!

Steve.