Compsci 100e, Spring 2011, Classwork 6 - Maps

Start by snarfing 06Clwk_maps. Work in groups of up to 3.

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Maps

Terminology

Definition
A map is an unordered collection of values each with distinct keys. The key-value pair stored within the map is called an entry.
The key is a distinct object that represents the entry as a whole.
The value is any object.
A map is sometimes also called a dictionary or table.

Using Maps

A Map might be used to associate student IDs with complete student records, or words to their definitions (like a real dictionary). What other examples of maps can you think of?

Using TreeMap

In Java, we can use the TreeMap class that implements the Map interface. In the remainder of this activity, you will use one or more TreeMap objects to discover several interesting properties about words in a file: how many times a word appears, on which lines a word appears, and at which locations does a word appear.

There is one class defined for this activity: WordLines. You should start by reading over the code in this class, so you can answer the following questions.

Part 1 - Reading Code

Explain the following details about the code in a README file:

  1. What is the purpose of the Integer object and how is it used in this class?
  2. Why is the output printed in sorted order?
  3. How does the method printResults work for any kind of map


Part 2 - For each word, which lines does it occur on?

Complete the method, getLineNumbers, that creates a new Map with words as the key and the set of line numbers on which that word appears as the value. This method should get the data for each word from the Scanner passed it.


Part 3 - For each letter, what are all the words that start with that letter?

Complete the method, getFrequencies, that creates a new Map with letters as the key and the set of words which start with that letter as the value. This method should get the data for each word from the Scanner passed it.


Part 4 - For each word, in a set of files, what are the locations of the word?

Suppose you want to create an inverted index, mapping from words to their locations in a set of documents. Describe how you would create this structure. What are the types of the value and key in your map? How do you create this map?

Submit WordLines.java and your README using submit folder clwk06-0210.