Learning objectives

• stream processing (finite vs. infinite/unbounded)
• pipes and filters architecture
• representing streams using the Iterator design pattern
• separation of processing and I/O concerns
• testability using the Observer design pattern
• time/space complexity and scalability

System requirements

• Java 21 LTS release (recommended) or later
• Maven 3.6.3 or later

You may also be able to install these requirements through your package manager or SDKMAN!.

Alternatively, you can use an IDE such as IntelliJ IDEA or Eclipse.

Description

This application maintains a running FIFO queue of the last n words read from the standard input (stdin). For each word read, the application prints the updated queue to the standard output (stdout) in the format

[w1, w2, ..., wn]

where wn is the most recent word read, and w1 is the oldest word still in the queue.

The default queue capacity is 10, and a different capacity can be passed as a command-line argument.

If multiple words are entered on the same line, the application processes them separately, using non-word characters, such as whitespace, as separators.

Examples

$ mvn compile exec:java -Dexec.mainClass="edu.luc.cs.consoleapp.Main" -Dexec.args="3"
[INFO] Scanning for projects...
[INFO] ...
[INFO] --- exec:3.1.0:java (default-cli) @ consoleapp ---
w1 w2
[w1]
[w1, w2]
w3
[w1, w2, w3]
w4 w5
[w2, w3, w4]
[w3, w4, w5]
w6
[w4, w5, w6]
^C

Running the application

Without command-line arguments:

$ mvn compile exec:java -Dexec.mainClass="edu.luc.cs.consoleapp.Main"

With a specific command-line argument (sliding queue capacity):

$ mvn compile exec:java -Dexec.mainClass="edu.luc.cs.consoleapp.Main" -Dexec.args="3"

Running a specific main class directly

$ mvn compile exec:java -Dexec.mainClass="edu.luc.cs.consoleapp.Main"

or

$ mvn compile exec:java -Dexec.mainClass="edu.luc.cs.consoleapp.MainLeaky" -Dexec.args="3"

or

$ mvn compile exec:java -Dexec.mainClass="edu.luc.cs.consoleapp.MainTestable" -Dexec.args="3"

Running the tests

$ mvn test

Generating the test coverage reports

$ mvn test jacoco:report

You can then view the full report in a web browser. (Note that this will get generated only after all tests pass.)

On macOS:

$ open target/site/jacoco/index.html

On Linux:

$ xdg-open target/site/jacoco/index.html

On Windows: please let me know if you know how to do this from the WSL command line. Otherwise you can open the index file in your web browser.

Note that the report will show 0% coverage as long as there are failing tests.

Running the application outside Maven

This uses the executable JAR with all dependencies included, avoiding the overhead of running through Maven:

On Linux or macOS:

$ mvn clean package
$ java -jar target/consoleapp-0.3-jar-with-dependencies.jar 3

On Windows:

> mvn clean package
> java -jar target\consoleapp-0.3-jar-with-dependencies.jar 3