Review the Starter Code

Before diving in and starting to code, make sure you understand what the code you’ve been given does. Since you’re starting with a functioning—albeit unfinished—program, go ahead and run it to get an idea of how it works.

Let’s explore the code by starting with the source of the data our program is providing access to.

The Data File: jobs_data.csv

Our simple app doesn’t connect to a database. If the prototype proves useful and we continue development, we’ll add that functionality later. But for now, we’ve been given a CSV (comma-separated values) file from the Company Team at LaunchCode that contains some recent jobs. This file was exported from an Excel spreadsheet into this format, which is easy for programs to read in.

If CSV files are new to you, don’t worry, they’re easy to understand. CSV files are conceptually similar to simple spreadsheets in that they organize data in rows and columns. The major difference is that they don’t have the ability to carry out calculations the way spreadsheets do, and you can easily open, read, and edit them in plain text editors.

Open up jobs_data.csv, which is in the src/main/java/resources folder. You’ll see that the first line is:

name,employer,location,position type,core competency

While it isn’t required, the first line of a CSV file often represents the column names. We have 5 names here, which indicates that each of our rows in the CSV file should have 5 fields. In this file format, a “row” corresponds to a new line. So each line below the first will constitute a row of data, or a record.

Have a look at the data below line 1, and ask yourself the following questions:

1. Which fields match up with which column names above?
2. Why do some lines/rows (e.g. line 10) have more commas than others, if commas are supposed to separate columns?
3. What role do the double-quotes play?

The TechJobs Class

The TechJobs class contains the main method that will drive our program’s functionality. It contains three methods:

1. main - The main application runner.
2. getUserSelection - A utility method that displays a menu of choices and returns the user’s selection.
3. printJobs - This is meant to print a list of jobs to the console in a nicely formatted manner, but hasn’t been implemented yet. This will be part of your job.

Let’s look at each of these.

The main Method

The logic within main presents menus in turn, and based on the user’s choice, takes appropriate action.

It begins by declaring two local variables: columnChoices and actionChoices. These contain information relating to the menus that we’ll display, and we’ll look at them in more detail later.

Next, we notice a while loop that starts while (true). While we usually want to avoid creating infinite loops, we have a good reason for doing so in this case! We want our application to continually run until the user decides they want to quit. The simplest way to do this is to loop forever. When the user wants to quit, they can enter x at the initial “View jobs by” prompt. As you saw above, however, IntelliJ’s Run pane works slightly differently and you’ll need to rely on the red “stop” icon to stop the program.

The main method can be summarized as follows:

1. Present the user with choices on how to view data: list or search.
2. Based on that choice, prompt them for the column to apply the choice to. In the case of a search, we also ask for a search term.
3. Carry out the request to the JobData class via one of its public methods.
4. Display the results of the request.
5. Repeat.

main simulates a query to an external source:

1. We ask the method for data that originates from a non-Java source.
2. The method parses and filters that data.
3. The method presents the data in a useful manner.

The getUserSelection Method

The getUserSelection method takes in a String to display above the menu, to provide context for what they are being asked. It also takes in a HashMap with String keys and String values. How is this used? What will this HashMap contain when the method runs?

To figure this out, right-click on the method name and select Find Usages. This will open a pane and display each location in the program where getUserSelection is called. The first such usage is the first line of the main while loop:

String actionChoice = getUserSelection("View jobs by:", actionChoices);

What is this HashMap named actionChoices? If we look a few lines above, we see:

// Top-level menu options
HashMap<String, String> actionChoices = new HashMap<>();
actionChoices.put("search", "Search");
actionChoices.put("list", "List");

If you recall how the program worked when you ran it, the first menu that you chose had two options, Search and List, which seem to correspond to the entries in actionChoices. This is, in fact, the case. This is the data that is used to generate the first menu we see when running the program.

The second usage of getUserSelection is a few lines below:

String columnChoice = getUserSelection("List", columnChoices);

This references columnChoices, which is declared at the top of main and has a similar structure to actionChoices (they’re the same data type and are used in calls to the same method, so this shouldn’t be surprising). Most of the entries in columnChoices correspond to columns in the jobs data set, but there’s one additional entry with key/value pair "all"/"All". These entries will help us present to the user the options for searching our data, which will correspond to searching within a given column, or searching all columns at once.

The keys in actionChoices and columnChoices represent the “internal” String we’ll use to refer to these options (e.g. when representing the user’s menu choice or querying data). The values in the map represent the “external” way that these are represented to the user.

Within getUserSelection itself, most of the code is within a do-while loop. A do-while loop is similar to a while loop, but the conditional check is at the end of the loop’s code block. This has the net consequence that the loop’s code block always runs at least once. At the end of the block’s execution, we check a condition to determine if we should run the block again. This nicely mimics the behavior of simple menu-driven applications.

Within this loop, menu options are printed to the screen, and user input is collected. If the input is valid, it returns the choice as a String to the caller. This String corresponds to the chosen key (from choices, which will be either actionChoices or columnChoices) of the item the user selected. If invalid, it re-prompts the user.

The local variable choiceKeys is used to easily enumerate the choices HashMap. In other words, it gives us a simple way to provide an ordering to choices, which doesn’t have an ordering of its own.

The JobData Class

The JobData class is responsible for importing the data from the CSV file and parsing it into a Java-friendly format, that is, into HashMap and ArrayList form. Look toward the bottom of the class, and you will see a method named loadData, which does just what it advertises. After parsing the file data, it stores the data in the private property allJobs, which is of type ArrayList<HashMap<String, String>>.

Let’s look more closely at the data type of allJobs. It purports to be an ArrayList that stores HashMap objects, which have String keys and String values. If we were to represent some of this data visually, using [] for an ArrayList and {} with key/value pairs, it would look like this:

[
    {
        "name": "Junior Data Analyst",
        "employer": "Lockerdome",
        "location": "Saint Louis",
        "position type": "Data Scientist / Business Intelligence",
        "core competency": "Statistical Analysis"
    },
    {
        "name": "Junior Web Developer",
        "employer": "Cozy",
        "location": "Portland",
        "position type": "Web - Back End",
        "core competency": "Ruby"
    },
    ...
]

If you look at the loadData method, you’ll see a lot of unfamiliar code. Blake wrote this essential piece of code for you, and while you won’t have to modify it, it will be useful to have an idea of how it works. Read through the code until you feel like you can describe its functionality at a basic level.

There are three more methods in JobData, each of which is public (and static, per our earlier note): findAll(), findAll(String), and findByColumnAndValue(String, String). Note that there are two methods named findAll, but this is allowed in Java via a feature called overloading. Overloading happens when multiple methods have the same name, but they each have different input parameters (also called argument lists). Read more about overloading .

Here are some questions to ask yourself while reading this code:

1. What is the data type of a “job” record?
2. Why does findAll(String) return something of type ArrayList<String> while findByColumnAndValue(String, String) and findAll() return something of type ArrayList<HashMap<String, String>>?
3. Why is loadData() called at the top of each of these four methods? Does this mean that we load the data from the CSV file each time one of them is called?