Writing a MadLibs System. MadLibs: Hours of Linguistic Fun! A Java Mad Lib System and Suggested Representation

Writing a MadLibs System                                                                                Page 1 of 4

MadLibs: Hours of Linguistic Fun!

Today we're going to implement a Mad Libs system. If you don't know what Mad Libs are, please tell us what rock you've been living under! (We're always looking for real estate investments and peaceful, secluded rocks command high prices in today's insecure world.) After you've informed us, visit madlibs.org to try out some Mad Libs.

The main idea is to create “funny” stories from a story template with key words missing. The missing words are filled in by asking the player for words of a certain type — such as a noun, number, or adjective. We call the missing words slots. In the old days, you'd walk uphill both ways in the snow to your friend's house to play with her Mad Libs book. Since we're at MIT, we'll dispense with the book and design a computer system instead. A computerized MadLibs system needs to permit creation and maintenance of Mad Libs, as well as permit users to actually do them.

A Java Mad Lib System and Suggested Representation

Getting the files

Today, we're going to have you make a new Java project in eclipse, and then copy the provided .java files into your src directory. To do this, open eclipse (using add eclipse-sdk, then elcipse). In Eclipse, select File->New->Java Project. 

A dialogue box will open. Select Java Project and click Next. Name the project "Lab 2". Keep the radio button on "Create project in workspace" (unlike last time where the project remained in your projects folder), but change the next radio button group to select "Create separate source and output folders". The last option will create a src directory for the .java files, and a bin directory for the class files. Click next.

We need to change the Java Settings to import JUnit.jar. This jar file allows you to use JUnit to run tests. You already have JUnit.jar in your lab1 project. Select the Libraries tab, and then select Add External Jar. Use the browser to find ...6.092/projects/lab1_project/junit.jar -- select the jar file and click ok. Then click Finish. This whole process sets up a .classpath and .project file at the root of your Lab 2 project in your workspace folder. You can check out these text files if you are curious  in the Labs section.

Now that you have a project, simply copy the .java files from /mit/iapjava into the src folder of the project you created. Type the following commands at the athena prompt: 

add iapjava cp -r /mit/iapjava/www/day2/lab2_project/* ~/6.092/workspace/Lab\ 2/src/

Note: after you have copied the .java files to the src directory, right click on the src folder in the package explorer of Eclipse and select "Refresh". Only then will you see the Java files in the src folder. 

If you have any problems, let a staff member know.

Writing a MadLibs System                                                                                Page 2 of 4

Task 0: Understanding the MadLibs ADT in Java

A reasonably sane specification for a MadLibs abstract data type is available from the  labs section as MadLibTemplate.java. For example, a “Hello <noun>!” Mad Lib would be programmed in our system with the following code:

ml.addString("Hello "); ml.addSlot("noun"); ml.addString("!");

// now go and do it! ml.doLib(ui);

Your first task is to understand our ADT by reading the MadLibTemplate.java file, looking at the specifications (in comments), and seeing how the code snippet above works.

Note that parts of the specification are actually captured as an _{abstract class} in the code; any object that sub-classes MadLibTemplate must contain implementations for the abstract methods in the class.

(Abstract methods are easy to pick out - they are the ones with the keyword _abstract in their signatures.)

Task 1: Implementing the ADT in Java

Write a Java class _MadLib that extends _{MadLibTemplate} and implements all the required methods. In the code we've given you — available from the  labs section — we've provided the

MadLibTemplate.java that you'll be subclassing, a starter MadLib.java, and a suite of JUnit test cases (_{MadLibTest.java}) to help you out.

Our test code only exercises the high-level _MadLib code, you can choose to implement the functions in the _MadLib class any way you wish. However, we suggest that you try to make maximal use of the Java type system and use some of the polymorphism that you just learned about. Two starts are provided below:

//Option 1 abstract class MadLibEntry {

/** @return the value of this entry in a template **/ abstract public String templateString();

/** @return the value of this entry in an actual madlib **/ abstract public String madLibString();

/**

* Collect any relevant information from the user for this entry  

**/ abstract public void doLib(UserInterface ui);

}

class TextEntry extends MadLibEntry { //What needs to go here?

}

class Slot extends MadLibEntry { //What needs to go here? }

Writing a MadLibs System                                                                                Page 3 of 4

//Option 2 interface class MadLibEntry {

/** @return the value of this entry in a template **/ abstract public String