Add pizza party exercise

durimkryeziu · durimkryeziu · commit 76330b51ba4e · 2026-03-30T00:32:59.000+02:00
Add the Pizza Party exercise as a standalone Gradle module with
console I/O adapters and tests for the purchase planner and prompt flow.

This gives the repository a runnable solution for exercise 8 while
keeping input validation and output formatting covered by tests.
diff --git a/.gitignore b/.gitignore
@@ -11,3 +11,5 @@ build/
 out/
 !**/src/main/**/out/
 !**/src/test/**/out/
+
+.DS_Store
diff --git a/README.md b/README.md
@@ -20,7 +20,7 @@ Exercises for Programmers: 57 Challenges to Develop Your Coding Skills by Brian
 
 **Calculations**
 - Exercise 7. [Area of a Rectangular Room](https://github.com/durimkryeziu/exercises-for-programmers-java/tree/main/area-rectangular-room)
-- Exercise 8. Pizza Party
+- Exercise 8. [Pizza Party](https://github.com/durimkryeziu/exercises-for-programmers-java/tree/main/pizza-party)
 - Exercise 9. Paint Calculator
 - Exercise 10. Self-Checkout
 - Exercise 11. Currency Conversion
diff --git a/pizza-party/build.gradle b/pizza-party/build.gradle
@@ -0,0 +1,8 @@
+plugins {
+    id 'dev.delivercraft.common-conventions'
+}
+
+dependencies {
+    testImplementation(libs.assertj.core)
+    testImplementation(libs.junit.jupiter)
+}
diff --git a/pizza-party/src/main/java/dev/delivercraft/pizza/InputStreamLineReader.java b/pizza-party/src/main/java/dev/delivercraft/pizza/InputStreamLineReader.java
@@ -0,0 +1,25 @@
+package dev.delivercraft.pizza;
+
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.InputStreamReader;
+import java.io.UncheckedIOException;
+
+final class InputStreamLineReader implements LineReader {
+
+    private final BufferedReader bufferedReader;
+
+    InputStreamLineReader(InputStream inputStream) {
+        this.bufferedReader = new BufferedReader(new InputStreamReader(inputStream));
+    }
+
+    @Override
+    public String readLine() {
+        try {
+            return this.bufferedReader.readLine();
+        } catch (IOException e) {
+            throw new UncheckedIOException(e);
+        }
+    }
+}
diff --git a/pizza-party/src/main/java/dev/delivercraft/pizza/LineReader.java b/pizza-party/src/main/java/dev/delivercraft/pizza/LineReader.java
@@ -0,0 +1,6 @@
+package dev.delivercraft.pizza;
+
+public interface LineReader {
+
+    String readLine();
+}
diff --git a/pizza-party/src/main/java/dev/delivercraft/pizza/LineWriter.java b/pizza-party/src/main/java/dev/delivercraft/pizza/LineWriter.java
@@ -0,0 +1,8 @@
+package dev.delivercraft.pizza;
+
+public interface LineWriter {
+
+    void write(String text);
+
+    void writeLine(String line);
+}
diff --git a/pizza-party/src/main/java/dev/delivercraft/pizza/Main.java b/pizza-party/src/main/java/dev/delivercraft/pizza/Main.java
@@ -0,0 +1,11 @@
+package dev.delivercraft.pizza;
+
+public final class Main {
+
+    void main() {
+        LineReader lineReader = new InputStreamLineReader(System.in);
+        LineWriter lineWriter = new OutputStreamLineWriter(System.out);
+        PizzaParty pizzaParty = new PizzaParty(lineReader, lineWriter);
+        pizzaParty.displayPizzaParty();
+    }
+}
diff --git a/pizza-party/src/main/java/dev/delivercraft/pizza/OutputStreamLineWriter.java b/pizza-party/src/main/java/dev/delivercraft/pizza/OutputStreamLineWriter.java
@@ -0,0 +1,24 @@
+package dev.delivercraft.pizza;
+
+import java.io.OutputStream;
+import java.io.PrintWriter;
+
+final class OutputStreamLineWriter implements LineWriter {
+
+    private final PrintWriter printWriter;
+
+    OutputStreamLineWriter(OutputStream outputStream) {
+        this.printWriter = new PrintWriter(outputStream, true);
+    }
+
+    @Override
+    public void write(String text) {
+        this.printWriter.print(text);
+        this.printWriter.flush();
+    }
+
+    @Override
+    public void writeLine(String line) {
+        this.printWriter.println(line);
+    }
+}
diff --git a/pizza-party/src/main/java/dev/delivercraft/pizza/PizzaParty.java b/pizza-party/src/main/java/dev/delivercraft/pizza/PizzaParty.java
@@ -0,0 +1,72 @@
+package dev.delivercraft.pizza;
+
+import java.util.Objects;
+
+final class PizzaParty {
+
+    private final LineReader lineReader;
+
+    private final LineWriter lineWriter;
+
+    PizzaParty(LineReader lineReader, LineWriter lineWriter) {
+        Objects.requireNonNull(lineReader, "lineReader must not be null");
+        Objects.requireNonNull(lineWriter, "lineWriter must not be null");
+        this.lineReader = lineReader;
+        this.lineWriter = lineWriter;
+    }
+
+    void displayPizzaParty() {
+        int people = toPeopleCount(readRequiredInput("How many people? "));
+        int pizzas = toNumber(readRequiredInput("How many pizzas do you have? "));
+        int slicesPerPizza = toNumber(readRequiredInput("How many slices per pizza? "));
+
+        int totalSlices = pizzas * slicesPerPizza;
+        int piecesPerPerson = totalSlices / people;
+        int leftoverPieces = totalSlices % people;
+
+        this.lineWriter.writeLine("");
+        this.lineWriter.writeLine("%d people with %d %s".formatted(people, pizzas,
+                pluralize(pizzas, "pizza", "pizzas")));
+        this.lineWriter.writeLine("Each person gets %d %s of pizza.".formatted(piecesPerPerson,
+                pluralize(piecesPerPerson, "piece", "pieces")));
+        this.lineWriter.writeLine("There %s %d %s.".formatted(verbForLeftover(leftoverPieces), leftoverPieces,
+                pluralize(leftoverPieces, "leftover piece", "leftover pieces")));
+    }
+
+    private String readRequiredInput(String prompt) {
+        this.lineWriter.write(prompt);
+        String input = this.lineReader.readLine();
+        if (input == null || input.isBlank()) {
+            throw new IllegalArgumentException("Input must not be empty!");
+        }
+        return input;
+    }
+
+    private static int toPeopleCount(String value) {
+        int people = toNumber(value);
+        if (people == 0) {
+            throw new IllegalArgumentException("Number of people must be greater than zero!");
+        }
+        return people;
+    }
+
+    private static int toNumber(String value) {
+        try {
+            int number = Integer.parseInt(value);
+            if (number < 0) {
+                throw new IllegalArgumentException("Please enter a positive number! Input: %d".formatted(number));
+            }
+            return number;
+        } catch (NumberFormatException e) {
+            throw new IllegalArgumentException("Please enter a valid number! Input: %s".formatted(value), e);
+        }
+    }
+
+    private static String pluralize(int value, String singular, String plural) {
+        return value == 1 ? singular : plural;
+    }
+
+    private static String verbForLeftover(int leftoverPieces) {
+        return leftoverPieces == 1 ? "is" : "are";
+    }
+}
diff --git a/pizza-party/src/main/java/dev/delivercraft/pizza/PizzaPurchasePlanner.java b/pizza-party/src/main/java/dev/delivercraft/pizza/PizzaPurchasePlanner.java
@@ -0,0 +1,68 @@
+package dev.delivercraft.pizza;
+
+import java.util.Objects;
+
+final class PizzaPurchasePlanner {
+
+    private static final int SLICES_PER_PIZZA = 8;
+
+    private final LineReader lineReader;
+
+    private final LineWriter lineWriter;
+
+    PizzaPurchasePlanner(LineReader lineReader, LineWriter lineWriter) {
+        Objects.requireNonNull(lineReader, "lineReader must not be null");
+        Objects.requireNonNull(lineWriter, "lineWriter must not be null");
+        this.lineReader = lineReader;
+        this.lineWriter = lineWriter;
+    }
+
+    void displayPizzaPurchasePlan() {
+        int people = toPeopleCount(readRequiredInput("How many people? "));
+        int piecesPerPerson = toNumber(readRequiredInput("How many pieces does each person want? "));
+
+        int requiredPieces = people * piecesPerPerson;
+        int requiredPizzas = divideRoundingUp(requiredPieces, SLICES_PER_PIZZA);
+
+        this.lineWriter.writeLine("");
+        this.lineWriter.writeLine("You will need to purchase %d %s.".formatted(
+                requiredPizzas, pluralize(requiredPizzas, "pizza", "pizzas")));
+    }
+
+    private String readRequiredInput(String prompt) {
+        this.lineWriter.write(prompt);
+        String input = this.lineReader.readLine();
+        if (input == null || input.isBlank()) {
+            throw new IllegalArgumentException("Input must not be empty!");
+        }
+        return input;
+    }
+
+    private static int toPeopleCount(String value) {
+        int people = toNumber(value);
+        if (people == 0) {
+            throw new IllegalArgumentException("Number of people must be greater than zero!");
+        }
+        return people;
+    }
+
+    private static int toNumber(String value) {
+        try {
+            int number = Integer.parseInt(value);
+            if (number < 0) {
+                throw new IllegalArgumentException("Please enter a positive number! Input: %d".formatted(number));
+            }
+            return number;
+        } catch (NumberFormatException e) {
+            throw new IllegalArgumentException("Please enter a valid number! Input: %s".formatted(value), e);
+        }
+    }
+
+    private static int divideRoundingUp(int value, int divisor) {
+        return (value + divisor - 1) / divisor;
+    }
+
+    private static String pluralize(int value, String singular, String plural) {
+        return value == 1 ? singular : plural;
+    }
+}
diff --git a/pizza-party/src/main/java/dev/delivercraft/pizza/PizzaPurchasePlannerMain.java b/pizza-party/src/main/java/dev/delivercraft/pizza/PizzaPurchasePlannerMain.java
@@ -0,0 +1,11 @@
+package dev.delivercraft.pizza;
+
+public final class PizzaPurchasePlannerMain {
+
+    void main() {
+        LineReader lineReader = new InputStreamLineReader(System.in);
+        LineWriter lineWriter = new OutputStreamLineWriter(System.out);
+        PizzaPurchasePlanner planner = new PizzaPurchasePlanner(lineReader, lineWriter);
+        planner.displayPizzaPurchasePlan();
+    }
+}
diff --git a/pizza-party/src/test/java/dev/delivercraft/pizza/InputStreamLineReaderTest.java b/pizza-party/src/test/java/dev/delivercraft/pizza/InputStreamLineReaderTest.java
@@ -0,0 +1,47 @@
+package dev.delivercraft.pizza;
+
+import org.junit.jupiter.api.Test;
+
+import java.io.ByteArrayInputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.UncheckedIOException;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
+
+class InputStreamLineReaderTest {
+
+    @Test
+    void readLine_GivenNoInput_ShouldReturnNull() {
+        ByteArrayInputStream inputStream = new ByteArrayInputStream(new byte[]{});
+        LineReader lineReader = new InputStreamLineReader(inputStream);
+
+        String result = lineReader.readLine();
+
+        assertThat(result).isNull();
+    }
+
+    @Test
+    void readLine_GivenInput_ShouldReturnInputLine() {
+        String input = "Hello, World!\n";
+        ByteArrayInputStream inputStream = new ByteArrayInputStream(input.getBytes());
+        LineReader lineReader = new InputStreamLineReader(inputStream);
+
+        String result = lineReader.readLine();
+
+        assertThat(result).isEqualTo("Hello, World!");
+    }
+
+    @Test
+    void readLine_GivenNullInputStream_ShouldThrowException() throws IOException {
+        @SuppressWarnings("PMD.CloseResource")
+        InputStream inputStream = InputStream.nullInputStream();
+        inputStream.close();
+
+        LineReader lineReader = new InputStreamLineReader(inputStream);
+
+        assertThatExceptionOfType(UncheckedIOException.class)
+                .isThrownBy(lineReader::readLine);
+    }
+}
diff --git a/pizza-party/src/test/java/dev/delivercraft/pizza/OutputStreamLineWriterTest.java b/pizza-party/src/test/java/dev/delivercraft/pizza/OutputStreamLineWriterTest.java
@@ -0,0 +1,32 @@
+package dev.delivercraft.pizza;
+
+import org.junit.jupiter.api.Test;
+
+import java.io.ByteArrayOutputStream;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class OutputStreamLineWriterTest {
+
+    @Test
+    void write_GivenText_ShouldPrintText() {
+        ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
+        LineWriter lineWriter = new OutputStreamLineWriter(outputStream);
+        String text = "Hello, World!";
+
+        lineWriter.write(text);
+
+        assertThat(outputStream).hasToString(text);
+    }
+
+    @Test
+    void writeLine_GivenText_ShouldPrintTextWithNewLine() {
+        ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
+        LineWriter lineWriter = new OutputStreamLineWriter(outputStream);
+        String line = "Hello, World!";
+
+        lineWriter.writeLine(line);
+
+        assertThat(outputStream).hasToString(line + System.lineSeparator());
+    }
+}
diff --git a/pizza-party/src/test/java/dev/delivercraft/pizza/PizzaPartyTest.java b/pizza-party/src/test/java/dev/delivercraft/pizza/PizzaPartyTest.java
diff --git a/pizza-party/src/test/java/dev/delivercraft/pizza/PizzaPurchasePlannerTest.java b/pizza-party/src/test/java/dev/delivercraft/pizza/PizzaPurchasePlannerTest.java
diff --git a/settings.gradle b/settings.gradle
