Project design
- Java course
- Advanced
- Lesson 78/82
- 6 min
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:
Streamfor filtering and groupingExecutorServicefor a concurrent totalreflectionand@interfacefor 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
Eventclass and anArrayList. - 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.
Practice 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.
Starter code
import java.util.ArrayList;
// Define the Event class (String type, int severity and a constructor)
public class Main {
public static void main(String[] args) {
// Declare ArrayList<Event> log
// Add two events (info 1, error 5)
// Print with for-each
}
}Sample 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);
}
}
}Expected output
info 1 error 5
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What should be the first step of the event log project?
- Write the reflection layer
- Define the Event model and the list Correct answer
- Add the concurrent layer
- Group with Stream
Explanation: Start with the Event model and the list; other layers build on it.
2 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____;class Event {
String type;
int severity;
Event(String type, int severity) {
this.type = type;
this.severity = severity;
}
}
Event e = new Event("info", 1);Explanation: The constructor call ends with a parenthesis and a semicolon.
3 Match the project layers
| Term | Meaning |
|---|---|
Model |
Event class |
Stream |
Filtering and grouping |
Concurrent |
Total via ExecutorService |
Reflection |
Marking with @Logged |