Learning objectives

• simple console app example
• experience with Git source code management
• building with Gradle
• 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 11 SDK or later
• Gradle

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 Android Studio.

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

$ java -cp build/lib/consoleapp-java-0.1-SNAPSHOT.jar hw.Main 3
w1 w2
[w1]
[w1, w2]
w3
[w1, w2, w3]
w4 w5
[w2, w3, w4]
[w3, w4, w5]
w6
[w4, w5, w6]
EOF

Running the application

For the remaining commands to work, you should be in the project root directory, e.g., /home/yourid/StudioProjects/cs313413f20p1a.

On Linux or Mac OS X:

$ ./gradlew run

or with an explicit argument and redirecting stdin from a sample file:

$ ./gradlew run --args="3" < build.gradle

On Windows:

> gradlew run

or with an explicit argument and redirecting stdin from a sample file:

> gradlew run --args="3" < build.gradle

Running the tests

On Linux or Mac OS X:

$ ./gradlew test

On Windows:

> gradlew test

Generating the test coverage reports

On Linux or Mac OS X:

$ ./gradlew jacocoTestReport

On Windows:

> gradlew jacocoTestReport

The formatted HTML test coverage report will show up in

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

On Linux, assuming you're in the project root directory, you can open the test coverage report from the command line:

$ xdg-open build/reports/jacoco/test/html/index.html

On Mac OS X, you can just use the open command:

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

Running the application outside Gradle

On Linux or Mac OS X:

$ ./gradlew jar startScript
$ ./build/scripts/consoleapp-java

On Windows:

> gradlew jar startScript
> build\scripts\consoleapp-java

This allows using the application as part of a pipeline:

$ yes hello | ./build/scripts/consoleapp-java | head -n 10

Furthermore, using the "fat" jar, which contains the application code plus its dependencies, one can choose among the various versions of the main application. This requires having the java executable in the execution path. Add command-line arguments and input/output redirect as needed.

On Linux or Mac OS X:

$ ./gradlew jar
$ java -cp build/lib/consoleapp-java-0.1-SNAPSHOT.jar hw.Main
$ java -cp build/lib/consoleapp-java-0.1-SNAPSHOT.jar hw.MainLeaky
$ java -cp build/lib/consoleapp-java-0.1-SNAPSHOT.jar hw.MainTestable

On Windows:

> gradlew jar
> java -cp build/lib/consoleapp-java-0.1-SNAPSHOT.jar hw.Main
> java -cp build/lib/consoleapp-java-0.1-SNAPSHOT.jar hw.MainLeaky
> java -cp build/lib/consoleapp-java-0.1-SNAPSHOT.jar hw.MainTestable