jinshunlee / addressbook-level1

A Java sample application for students. An AddressBook application written in procedural fashion.

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AddressBook (Level 1)

  • This is a CLI (Command Line Interface) Address Book application written in procedural fashion.
  • It is a Java sample application intended for students learning Software Engineering while using Java as the main programming language.
  • It provides a reasonably well-written code example that is significantly bigger than what students usually write in data structure modules.
  • It can be used to achieve a number of beginner-level learning outcomes without running into the complications of OOP or GUI programmings.

Table of Contents

User Guide

This product is not meant for end-users and therefore there is no user-friendly installer. Please refer to the Setting up section to learn how to set up the project.

Starting the program

Using Eclipse

  1. Find the project in the Project Explorer or Package Explorer (usually located at the left side)
  2. Right click on the project
  3. Click Run As > Java Application
  4. The program now should run on the Console (usually located at the bottom side)
  5. Now you can interact with the program through the Console

Using Command Line

  1. 'Build' the project using Eclipse
  2. Open the Terminal/Command Prompt
  3. cd into the project's bin directory
  4. Type java seedu.addressbook.AddressBook, then Enter to execute
  5. Now you can interact with the program through the CLI

List of commands

Viewing help: help

Format: help

Help is also shown if you enter an incorrect command e.g. abcd

Adding a person: add

Adds a person to the address book


Words in UPPER_CASE are the parameters
Phone number and email can be in any order but the name must come first.


  • add John Doe p/98765432 e/johnd@gmail.com
  • add Betsy Crowe e/bencrowe@gmail.com p/1234567

Listing all persons: list

Shows a list of persons, as an indexed list, in the order they were added to the address book, oldest first.

Format: list

Finding a person by keyword find

Finds persons that match given keywords


The search is case sensitive, the order of the keywords does not matter, only the name is searched, and persons matching at least one keyword will be returned (i.e. OR search).


  • find John

    Returns John Doe but not john

  • find Betsy Tim John

    Returns Any person having names Betsy, Tim, or John

Deleting a person: delete

Format: delete INDEX

Deletes the person at the specified INDEX. The index refers to the index numbers shown in the most recent listing.


  • list
    delete 2

    Deletes the 2nd person in the address book.

  • find Betsy
    delete 1

    Deletes the 1st person in the results of the find command.

Clearing all entries: clear

Clears all entries from the address book.
Format: clear

Exiting the program: exit

Format: exit

Saving the data

Address book data are saved in the hard disk automatically after any command that changes the data. There is no need to save manually.

Changing the save location

Address book data are saved in a file called addressbook.txt in the project root folder. You can change the location by specifying the file path as a program argument.


  • java seedu.addressbook.AddressBook mydata.txt
  • java seedu.addressbook.AddressBook myFolder/mydata.txt

The file path must contain a valid file name and a valid parent directory.
File name is valid if it has an extension and no reserved characters (OS-dependent).
Parent directory is valid if it exists.
Note for non-Windows users: if the file already exists, it must be a 'regular' file.

When running the program inside Eclipse, there is a way to set command line parameters before running the program.

Developer Guide

Setting up


  • JDK 8 or later
  • Eclipse IDE

Importing the project into Eclipse

  1. Open Eclipse
  2. Click File > Import
  3. Click General > Existing Projects into Workspace > Next
  4. Click Browse, then locate the project's directory
  5. Click Finish


AddressBook saves data in a plain text file, one line for each person, in the format NAME p/PHONE e/EMAIL. Here is an example:

John Doe p/98765432 e/johnd@gmail.com
Jane Doe p/12346758 e/jane@gmail.com

All person data are loaded to memory at start up and written to the file after any command that mutates data. In-memory data are held in a ArrayList<String[]> where each String[] object represents a person.



  1. Open a DOS window in the test folder
  2. Run the runtests.bat script
  3. If the script reports that there is no difference between actual.txt and expected.txt, the test has passed.


  1. Open a terminal window in the test folder
  2. Run the runtests.sh script
  3. If the script reports that there is no difference between actual.txt and expected.txt, the test has passed.

Troubleshooting test failures

  • Problem: How do I examine the exact differences between actual.txt and expected.txt?
    Solution: You can use a diff/merge tool with a GUI e.g. WinMerge (on Windows)
  • Problem: The two files look exactly the same, but the test script reports they are different.
    Solution: This can happen because the line endings used by Windows is different from Unix-based OSes. Convert the actual.txt to the format used by your OS using some utility.
  • Problem: Test fails during the very first time.
    Solution: The output of the very first test run could be slightly different because the program creates a new storage file. Tests should pass from the 2nd run onwards.

Learning Outcomes

Learning Outcomes are the things you should be able to do after studying this code and completing the corresponding exercises.

Set up a project in an IDE [LO-IdeSetup]

Exercise: Setup project in Eclipse

  • Learn [how to set up a new project in Eclipse] (https://se-edu.github.io/addressbook-level1/doc/Getting started with Eclipse.pptx).
    Create a new project in Eclipse and write a small HelloWorld program.
  • Download the source code for this project: Click on the clone or download link above and either,
    1. download as a zip file and unzip content.
    2. clone the repo (if you know how to use Git) to your Computer.
  • Set up the project in Eclipse.
  • Run the program from within Eclipse, and try the features described in the User guide section

Navigate code efficiently [LO-CodeNavigation]

The AddressBook.java code is rather long, which makes it cumbersome to navigate by scrolling alone. Navigating code using IDE shortcuts is a more efficient option. For example, F3 will navigate to the definition of the method/field at the cursor.

Exercise: Learn to navigate code using shortcuts

Learn some Eclipse code navigation shortcuts (you can use Web resources like this one). For example, learn the shortcuts to,

  • go to the definition of a method.
  • go back to the previous location.
  • view the documentation of a method from where the method is being used, without navigating to the method itself.
  • find where a method/field is being used.
  • ...

Use a debugger [LO-Debugging]

Exercise: Learn to step through code using the debugger

Prerequisite: [LO-IdeSetup]

Learn Eclipse debugging features from [these slides](https://se-edu.github.io/addressbook-level1/doc/Debugging with Eclipse.pptx) or other online resources.
Demonstrate your debugging skills using the AddressBook code.

Here are some things you can do in your demonstration:

  1. Set a 'break point'
  2. Run the program in debug mode
  3. 'Step through' a few lines of code while examining variable values
  4. 'Step into', and 'step out of', methods as you step through the code
  5. ...

Automate CLI testing [LO-AutomatedCliTesting]

Exercise: Practice automated CLI testing

  • Run the tests as explained in the Testing section.
  • Examine the test script to understand how the script works.
  • Add a few more tests to the input.txt. Run the tests. It should fail.
    Modify expected.txt to make the tests pass again.
  • Edit the AddressBook.java to modify the behavior slightly and modify tests to match.

Use Collections [LO-Collections]

Note how the AddressBook class uses ArrayList<> class (from the Java Collections library) to store a list of String or String[] objects.

Resources: ArrayList class tutorial (from javaTpoint.com)

Exercise: Use HashMap

Currently, a person's details are stored as a String[]. Modify the code to use a HashMap<String, String> instead. A sample code snippet is given below.

private static final String PERSON_PROPERTY_NAME = "name";
private static final String PERSON_PROPERTY_EMAIL = "email";
HashMap<String,String> john = new HashMap<>();
john.put(PERSON_PROPERTY_NAME, "John Doe");
john.put(PERSON_PROPERTY_EMAIL, "john.doe@email.com");

Resources: HashMap tutorial (from beginnersbook.com)

Use Enums [LO-Enums]

Exercise: Use HashMap + Enum

Similar to the exercise in the LO-Collections section, but also bring in Java enum feature.

private enum PersonProperty  {NAME, EMAIL, PHONE};
HashMap<PersonProperty,String> john = new HashMap<>();
john.put(PersonProperty.NAME, "John Doe");
john.put(PersonProperty.EMAIL, "john.doe@email.com");

Use Varargs [LO-Varargs]

Note how the showToUser method uses Java Varargs feature .

Exercise: Use Varargs

Modify the code to remove the use of the Varargs feature. Compare the code with and without the varargs feature.

Follow a coding standard [LO-CodingStandard]

The given code follows the coding standard for the most part.

This learning outcome is covered by the exercise in [LO-Refactor].

Apply coding best practices [LO-CodingBestPractices]

Most of the given code follows the best practices mentioned in this document.

This learning outcome is covered by the exercise in [LO-Refactor]

Refactor code [LO-Refactor]


Exercise: Refactor the code to make it better

Note: this exercise covers two other Learning Outcomes: [LO-CodingStandard], [LO-CodingBestPractices]

  • Improve the code in the following ways,
    • Fix coding standard violations.
    • Fix violations of the best practices given in in this document.
    • Any other change that you think will improve the quality of the code.
  • Try to do the modifications as a combination of standard refactorings given in this catalog
  • As far as possible, use automated refactoring features in Eclipse.
  • If you know how to use Git, commit code after each refactoring.
    In the commit message, mention which refactoring you applied.
    Example commit messages: Extract variable isValidPerson, Inline method isValidPerson()
  • Remember to run the test script after each refactoring to prevent regressions.

Abstract methods well [LO-MethodAbstraction]

Notice how most of the methods in AddressBook are short and focused (does only one thing and does it well).

Case 1. Consider the following three lines in the main method.

    String userCommand = getUserInput();
    String feedback = executeCommand(userCommand);

If we include the code of echoUserCommand(String) method inside the getUserInput() (resulting in the code given below), the behavior of AddressBook remains as before. However, that is a not a good approach because now the getUserInput() is doing two distinct things. A well-abstracted method should do only one thing.

    String userCommand = getUserInput(); //also echos the command back to the user
    String feedback = executeCommand(userCommand);

Case 2. Consider the method removePrefixSign(String s, String sign). While it is short, there are some problems with how it has been abstracted.

  1. It contains the term sign which is not a term used by the AddressBook vocabulary.

    A method adds a new term to the vocabulary used to express the solution. Therefore, it is not good when a method name contains terms that are not strictly necessary to express the solution (e.g. there is another term already used to express the same thing) or not in tune with the solution (e.g. it does not go well with the other terms already used).

  2. Its implementation is not doing exactly what is advertised by the method name and the header comment. For example, the code does not remove only prefixes; it removes sign from anywhere in the s.

  3. The method can be more general and more independent from the rest of the code. For example, the method below can do the same job, but is more general (works for any string, not just parameters) and is more independent from the rest of the code (not specific to AddressBook)

     * Removes prefix from the given fullString if prefix occurs at the start of the string.
     private static String removePrefix(String fullString, String prefix) { ... }

    If needed, a more AddressBook-specific method that works on parameter strings only can be defined. In that case, that method can make use of the more general method suggested above.

Exercise: Improve abstraction of method

Refactor the method removePrefixSign as suggested above.


Notice how most of the methods in AddressBook are written at a single level of abstraction (cf SLAP)

Here is an example:

    public static void main(String[] args) {
        while (true) {
            userCommand = getUserInput();
            String feedback = executeCommand(userCommand);

Exercise 1: Reduce SLAP of method

In the main method, replace the processProgramArgs(args) call with the actual code of that method. The main method no longer has SLAP. Notice how mixing low level code with high level code reduces readability.

Exercise 2: Refactor the code to make it worse!

Sometimes, going in the wrong direction can be a good learning experience too. In this exercise, we explore how low code qualities can go.

  • Refactor the code to make the code as bad as possible.
    i.e. How bad can you make it without breaking the functionality while still making it look like it was written by a programmer (but a very bad programmer :-)).
  • In particular, inlining methods can worsen the code quality fast.

Work in a 1kLoC code base[LO-1KLoC]

Exercise: Enhance the code

Enhance the AddressBook to prove that you can work in a codebase of 1KLoC.
Remember to change code in small steps, update/run tests after each change, and commit after each significant change.

Some suggested enhancements:

  • Make the find command case insensitive e.g. find john should match John
  • Add a sort command that can list the persons in alphabetical order
  • Add an edit command that can edit properties of a specific person
  • Add an additional field (like date of birth) to the person record


Contact Us

  • Bug reports, Suggestions: Post in our issue tracker if you noticed bugs or have suggestions on how to improve.
  • Contributing: We welcome pull requests. Follow the process described here


A Java sample application for students. An AddressBook application written in procedural fashion.

License:MIT License


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