Project design

Design the advanced final skeleton.

Project: Event log

In this 5-lesson project you will build an event log application. Each lesson adds one piece; the final lesson combines them all.

You will use advanced topics together:

Stream for filtering and grouping
ExecutorService for a concurrent total
reflection and @interface for custom marking

The model class is Event: it holds a type and a severity level. Each lesson includes the previous lesson's solution as initial code.

Project flow

The project has four layers. Each layer uses the previous one's solution:

Model: the Event class and an ArrayList.
Stream: filtering and groupingBy.
Concurrent: total severity computed with ExecutorService.
Reflection: calling a method marked with @Logged.

In the final lesson all layers run together in main. The outputs are deterministic, so the expected output is the same every time.

Exercise Define the Event model and the list

Define an Event class with String type and int severity fields and a constructor. In Main, declare ArrayList<Event> log; add two events (info 1, error 5). Use a for-each loop to print each event as type + " " + severity.

Show example solution

import java.util.ArrayList;

class Event {
    String type;
    int severity;
    Event(String type, int severity) {
        this.type = type;
        this.severity = severity;
    }
}

public class Main {
    public static void main(String[] args) {
        ArrayList<Event> log = new ArrayList<>();
        log.add(new Event("info", 1));
        log.add(new Event("error", 5));
        for (Event e : log) {
            System.out.println(e.type + " " + e.severity);
        }
    }
}

Test yourself

What should be the first step of the event log project?
- Write the reflection layer
- Define the Event model and the list
- Add the concurrent layer
- Group with Stream
Show answer

Define the Event model and the list — Start with the Event model and the list; other layers build on it.

Complete the Event constructor call

class Event {
    String type;
    int severity;
    Event(String type, int severity) {
        this.type = type;
        this.severity = severity;
    }
}

Event e = new Event("info", 1____;

Show answer

class Event {
    String type;
    int severity;
    Event(String type, int severity) {
        this.type = type;
        this.severity = severity;
    }
}

Event e = new Event("info", 1);

Match the project layers

Model

Event class
Stream

Filtering and grouping
Concurrent

Total via ExecutorService
Reflection

Marking with @Logged

Next lesson: Stream layer

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