Java Java Data Structures Efficiency! Using a Map to store Contact Methods

Simon Andersson
Simon Andersson
6,880 Points

Code challenge 2/3, return the keys from a hashmap?

Okay so I'm pretty lost on HashMaps, keySets, LinkedLists and these things. I would still have a hard time explaining what a HashMap or keySet is to someone or why you would use it.

Anyhow, I've tried using the docs to solve this but I cant figure it out. If I've understood this correct, a HashMap has a Key and a Value, where the Value is accessed via the corresponding key, and keySets store keys from a HashMap?

And therefore I'm supposed to create a new keySet in the getAvailableContactMethods function to store the Keys from the mContactMethods HashMap?

Help is greatly appreciated, and if I'm totally wrong about keySets and HashMaps, feel free to leave a brief summary or explanation. Thanks =)

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

import java.util.Map;
import java.util.Set;
import java.util.HashMap;

public class Contact {
  private String mFirstName;
  private String mLastName;
  private Map<String, String> mContactMethods;

  public Contact(String firstName, String lastName) {
    mFirstName = firstName;
    mLastName = lastName;
    /* This stores contact methods by name
     * eg:  "phone" => "(555) 555-1234"
     */
    mContactMethods = new HashMap<String, String>();
  }

  public void addContactMethod(String method, String value) {
    // TODO: Add to the contact method map

    mContactMethods.put(method, value);


  }

  /**
   * Returns the available contact methods.  eg: phone, pager,
   *
   * @return The name of the contact methods that are available
   */
  public Set<String> getAvailableContactMethods() {
    // FIXME: This should return the current contact method names.
    Set<String> keyNames = new keySet<String>();
    for(String s : mContactMethods) // I know something is missing here.
      keyNames.add(s);

    return keyContactMethods; // I highly doubt this is correct.
  }

  /**
   * Returns the value for the contact method if it exists, 
   *
   * @param methodName  The name of the contact method to look up.
   * @return The name of the contact methods that are available
   */
  public String getContactInfo(String methodName) {
    // FIXME: return the value for the passed in *methodName*
    return null;
  }

  public String getFirstName() {
    return mFirstName;
  }

  public String getLastName() {
    return mLastName;
  }

}

1 Answer

Simon Coates
Simon Coates
28,653 Points

Most languages will have some method to get you sets or keys or values.

public Set<String> getAvailableContactMethods() {
    // FIXME: This should return the current contact method names.
    return mContactMethods.keySet();
  }