Project design
- Java course
- Advanced
- Lesson 73/82
- 6 min
Design the advanced project skeleton.
Project: Ledger
In this 5-lesson project you will build a ledger application. Each lesson adds one piece; the final lesson combines them all.
You will use advanced topics together:
Streamfor filtering and groupingExecutorServicefor concurrent total@Testfor a unit test
The model class is Transaction: it holds a category and an amount. Each lesson includes the previous lesson's solution as initial code, so the app grows step by step.
Project flow
The project has four layers. Each layer uses the previous one's solution:
- Model: the
Transactionclass and anArrayList. - Stream: filtering and
groupingBy. - Concurrent: a total computed with
ExecutorService. - Test:
LedgerServiceTestwith@Test.
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 model and the list
Define a Transaction class with String category and int amount fields and a constructor. In Main, declare ArrayList<Transaction> ledger; add two records (market 120, fuel 80). Use a for-each loop to print each record as category + " " + amount.
Starter code
import java.util.ArrayList;
// Define the Transaction class (String category, int amount and a constructor)
public class Main {
public static void main(String[] args) {
// Declare ArrayList<Transaction> ledger
// Add two records (market 120, fuel 80)
// Print with for-each
}
}Sample solution
import java.util.ArrayList;
class Transaction {
String category;
int amount;
Transaction(String category, int amount) {
this.category = category;
this.amount = amount;
}
}
public class Main {
public static void main(String[] args) {
ArrayList<Transaction> ledger = new ArrayList<>();
ledger.add(new Transaction("market", 120));
ledger.add(new Transaction("fuel", 80));
for (Transaction t : ledger) {
System.out.println(t.category + " " + t.amount);
}
}
}Expected output
market 120 fuel 80
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 ledger project?
- Define the model and the base list Correct answer
- Add the concurrent layer
- Write the test layer
- Group with Stream
Explanation: Start with the model and the base list; other layers build on it.
2 Complete the model constructor call
class Transaction {
String category;
int amount;
Transaction(String category, int amount) {
this.category = category;
this.amount = amount;
}
}
Transaction t = new Transaction("market", 120____;class Transaction {
String category;
int amount;
Transaction(String category, int amount) {
this.category = category;
this.amount = amount;
}
}
Transaction t = new Transaction("market", 120);Explanation: The constructor call ends with a parenthesis and a semicolon.
3 Match the project layers
| Term | Meaning |
|---|---|
Model |
Transaction class |
Stream |
Filtering and grouping |
Concurrent |
Total via ExecutorService |
Test |
Unit test with @Test |