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
• Gradle 9.3 or later (using Gradle Wrapper)

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

$ ./gradlew run --args="3"
> Task :run
w1 w2
[w1]
[w1, w2]
w3
[w1, w2, w3]
w4 w5
[w2, w3, w4]
[w3, w4, w5]
w6
[w4, w5, w6]
^D

Running the application

Without command-line arguments:

$ ./gradlew run

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

$ ./gradlew run --args="3"

Running a specific main class directly

$ ./gradlew run

or

$ ./gradlew run -PmainClass=edu.luc.cs.consoleapp.MainLeaky --args="3"

or

$ ./gradlew run -PmainClass=edu.luc.cs.consoleapp.MainTestable --args="3"

Running the tests

$ ./gradlew test

Generating the test coverage reports

$ ./gradlew test jacocoTestReport

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 build/reports/jacoco/test/html/index.html

On Linux:

$ xdg-open build/reports/jacoco/test/html/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 Gradle

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

On Linux or macOS:

$ ./gradlew clean shadowJar
$ java -jar build/libs/consoleapp-0.3-jar-with-dependencies.jar 3

On Windows:

> gradlew clean shadowJar
> java -jar build\libs\consoleapp-0.3-jar-with-dependencies.jar 3

Running with a different main class

To run a different main class (e.g., MainLeaky) using the standalone JAR, use the -cp (classpath) option with the fully qualified class name:

On Linux or macOS:

$ java -cp build/libs/consoleapp-0.3-jar-with-dependencies.jar edu.luc.cs.consoleapp.MainLeaky 3

On Windows:

> java -cp build\libs\consoleapp-0.3-jar-with-dependencies.jar edu.luc.cs.consoleapp.MainLeaky 3

Similarly, for other main classes:

$ java -cp build/libs/consoleapp-0.3-jar-with-dependencies.jar edu.luc.cs.consoleapp.MainTestable 3
$ java -cp build/libs/consoleapp-0.3-jar-with-dependencies.jar edu.luc.cs.consoleapp.MainStream 3