Add paint calculator exercise

durimkryeziu · durimkryeziu · commit 3ac774ab3a1b · 2026-05-24T01:50:20.000+02:00
diff --git a/README.md b/README.md
@@ -21,7 +21,7 @@ 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](https://github.com/durimkryeziu/exercises-for-programmers-java/tree/main/pizza-party)
-- Exercise 9. Paint Calculator
+- Exercise 9. [Paint Calculator](https://github.com/durimkryeziu/exercises-for-programmers-java/tree/main/paint-calculator)
 - Exercise 10. Self-Checkout
 - Exercise 11. Currency Conversion
 - Exercise 12. Computing Simple Interest
diff --git a/config/pmd/ruleset.xml b/config/pmd/ruleset.xml
@@ -86,7 +86,11 @@
     <rule ref="category/java/codestyle.xml/LocalHomeNamingConvention"/>
     <rule ref="category/java/codestyle.xml/LocalInterfaceSessionNamingConvention"/>
     <rule ref="category/java/codestyle.xml/LocalVariableNamingConventions"/>
-    <rule ref="category/java/codestyle.xml/LongVariable"/>
+    <rule ref="category/java/codestyle.xml/LongVariable">
+        <properties>
+            <property name="minimum" value="25"/>
+        </properties>
+    </rule>
     <rule ref="category/java/codestyle.xml/MethodNamingConventions">
         <properties>
             <property name="junit5TestPattern" value="^[a-z][a-zA-Z0-9]*(_[a-zA-Z0-9]+)*$"/>
@@ -166,7 +170,9 @@
     <rule ref="category/java/design.xml/UseObjectForClearerAPI"/>
     <!--  Design  -->
 
-    <rule ref="category/java/errorprone.xml"/>
+    <rule ref="category/java/errorprone.xml">
+        <exclude name="AvoidFieldNameMatchingMethodName"/>
+    </rule>
     <rule ref="category/java/multithreading.xml"/>
     <rule ref="category/java/performance.xml"/>
     <rule ref="category/java/security.xml"/>
diff --git a/paint-calculator/build.gradle b/paint-calculator/build.gradle
@@ -0,0 +1,10 @@
+plugins {
+    id 'dev.delivercraft.common-conventions'
+}
+
+dependencies {
+    implementation(project(':line-io'))
+    testImplementation(testFixtures(project(':line-io')))
+    testImplementation(libs.assertj.core)
+    testImplementation(libs.junit.jupiter)
+}
diff --git a/paint-calculator/src/main/java/dev/delivercraft/paint/Main.java b/paint-calculator/src/main/java/dev/delivercraft/paint/Main.java
@@ -0,0 +1,16 @@
+package dev.delivercraft.paint;
+
+import dev.delivercraft.io.InputStreamLineReader;
+import dev.delivercraft.io.LineReader;
+import dev.delivercraft.io.LineWriter;
+import dev.delivercraft.io.OutputStreamLineWriter;
+
+public final class Main {
+
+    void main() {
+        LineReader lineReader = new InputStreamLineReader(System.in);
+        LineWriter lineWriter = new OutputStreamLineWriter(System.out);
+        PaintCalculator calculator = new PaintCalculator(lineReader, lineWriter);
+        calculator.calculatePaint();
+    }
+}
diff --git a/paint-calculator/src/main/java/dev/delivercraft/paint/PaintCalculator.java b/paint-calculator/src/main/java/dev/delivercraft/paint/PaintCalculator.java
@@ -0,0 +1,33 @@
+package dev.delivercraft.paint;
+
+import dev.delivercraft.io.LineReader;
+import dev.delivercraft.io.LineWriter;
+
+import java.util.Objects;
+
+final class PaintCalculator {
+
+    private final LineReader lineReader;
+
+    private final LineWriter lineWriter;
+
+    PaintCalculator(LineReader lineReader, LineWriter lineWriter) {
+        this.lineReader = Objects.requireNonNull(lineReader, "lineReader must not be null");
+        this.lineWriter = Objects.requireNonNull(lineWriter, "lineWriter must not be null");
+    }
+
+    void calculatePaint() {
+        RoomDimension length = readDimension("What is the length of the room in feet? ");
+        RoomDimension width = readDimension("What is the width of the room in feet? ");
+
+        PaintEstimate estimate = PaintEstimator.estimate(new RoomDimensions(length, width));
+
+        this.lineWriter.writeLine("You will need to purchase %s %s of paint to cover %s square feet."
+                .formatted(estimate.gallons(), estimate.gallonWord(), estimate.area()));
+    }
+
+    private RoomDimension readDimension(String prompt) {
+        this.lineWriter.write(prompt);
+        return RoomDimension.of(this.lineReader.readLine());
+    }
+}
diff --git a/paint-calculator/src/main/java/dev/delivercraft/paint/PaintEstimate.java b/paint-calculator/src/main/java/dev/delivercraft/paint/PaintEstimate.java
@@ -0,0 +1,32 @@
+package dev.delivercraft.paint;
+
+import java.math.BigDecimal;
+import java.math.BigInteger;
+import java.util.Objects;
+
+final class PaintEstimate {
+
+    private final BigDecimal area;
+
+    private final BigInteger gallons;
+
+    PaintEstimate(BigDecimal area, BigInteger gallons) {
+        this.area = Objects.requireNonNull(area, "area must not be null");
+        this.gallons = Objects.requireNonNull(gallons, "gallons must not be null");
+    }
+
+    BigInteger gallons() {
+        return this.gallons;
+    }
+
+    String area() {
+        return this.area.stripTrailingZeros().toPlainString();
+    }
+
+    String gallonWord() {
+        if (BigInteger.ONE.equals(this.gallons)) {
+            return "gallon";
+        }
+        return "gallons";
+    }
+}
diff --git a/paint-calculator/src/main/java/dev/delivercraft/paint/PaintEstimator.java b/paint-calculator/src/main/java/dev/delivercraft/paint/PaintEstimator.java
@@ -0,0 +1,22 @@
+package dev.delivercraft.paint;
+
+import java.math.BigDecimal;
+import java.math.BigInteger;
+import java.math.RoundingMode;
+import java.util.Objects;
+
+final class PaintEstimator {
+
+    private static final int SQUARE_FEET_PER_GALLON = 350;
+
+    private PaintEstimator() {
+    }
+
+    static PaintEstimate estimate(RoomDimensions dimensions) {
+        Objects.requireNonNull(dimensions, "dimensions must not be null");
+        BigDecimal area = dimensions.area();
+        BigInteger gallons = area.divide(BigDecimal.valueOf(SQUARE_FEET_PER_GALLON), 0, RoundingMode.CEILING)
+                .toBigIntegerExact();
+        return new PaintEstimate(area, gallons);
+    }
+}
diff --git a/paint-calculator/src/main/java/dev/delivercraft/paint/RoomDimension.java b/paint-calculator/src/main/java/dev/delivercraft/paint/RoomDimension.java
@@ -0,0 +1,37 @@
+package dev.delivercraft.paint;
+
+import java.math.BigDecimal;
+import java.util.Objects;
+import java.util.regex.Pattern;
+
+record RoomDimension(BigDecimal value) {
+
+    private static final Pattern PLAIN_DECIMAL = Pattern.compile("\\d+(\\.\\d+)?");
+
+    RoomDimension {
+        Objects.requireNonNull(value, "value must not be null");
+        if (BigDecimal.ZERO.compareTo(value) >= 0) {
+            throw new IllegalArgumentException("Please enter a positive number! Input: %s".formatted(value));
+        }
+        value = value.stripTrailingZeros();
+    }
+
+    static RoomDimension of(String input) {
+        if (input == null || input.isBlank()) {
+            throw new IllegalArgumentException("Input must not be empty!");
+        }
+
+        String trimmedInput = input.trim();
+        if (!PLAIN_DECIMAL.matcher(trimmedInput).matches()) {
+            throw new IllegalArgumentException("Please enter a valid number! Input: %s".formatted(trimmedInput));
+        }
+
+        BigDecimal number = new BigDecimal(trimmedInput);
+        return new RoomDimension(number);
+    }
+
+    @Override
+    public String toString() {
+        return this.value.toPlainString();
+    }
+}
diff --git a/paint-calculator/src/main/java/dev/delivercraft/paint/RoomDimensions.java b/paint-calculator/src/main/java/dev/delivercraft/paint/RoomDimensions.java
@@ -0,0 +1,16 @@
+package dev.delivercraft.paint;
+
+import java.math.BigDecimal;
+import java.util.Objects;
+
+record RoomDimensions(RoomDimension length, RoomDimension width) {
+
+    RoomDimensions {
+        Objects.requireNonNull(length, "length must not be null");
+        Objects.requireNonNull(width, "width must not be null");
+    }
+
+    BigDecimal area() {
+        return this.length.value().multiply(this.width.value());
+    }
+}
diff --git a/paint-calculator/src/test/java/dev/delivercraft/paint/MainTest.java b/paint-calculator/src/test/java/dev/delivercraft/paint/MainTest.java
@@ -0,0 +1,42 @@
+package dev.delivercraft.paint;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import java.io.ByteArrayInputStream;
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.PrintStream;
+import java.nio.charset.StandardCharsets;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.parallel.ResourceLock;
+import org.junit.jupiter.api.parallel.Resources;
+
+class MainTest {
+
+    @Test
+    @ResourceLock("SYSTEM_IN")
+    @ResourceLock(Resources.SYSTEM_OUT)
+    @SuppressWarnings("PMD.CloseResource")
+    void main_GivenValidInput_ShouldPrintPaintEstimate() throws IOException {
+        InputStream originalInput = System.in;
+        PrintStream originalOutput = System.out;
+        String inputText = "18%n20%n".formatted();
+        ByteArrayInputStream input = new ByteArrayInputStream(inputText.getBytes(StandardCharsets.UTF_8));
+        ByteArrayOutputStream output = new ByteArrayOutputStream();
+
+        try (input; output; PrintStream printStream = new PrintStream(output, true, StandardCharsets.UTF_8)) {
+            System.setIn(input);
+            System.setOut(printStream);
+
+            new Main().main();
+
+            assertThat(output.toString(StandardCharsets.UTF_8)).contains(
+                    "You will need to purchase 2 gallons of paint to cover 360 square feet.");
+        } finally {
+            System.setIn(originalInput);
+            System.setOut(originalOutput);
+        }
+    }
+}
diff --git a/paint-calculator/src/test/java/dev/delivercraft/paint/PaintCalculatorTest.java b/paint-calculator/src/test/java/dev/delivercraft/paint/PaintCalculatorTest.java
@@ -0,0 +1,127 @@
+package dev.delivercraft.paint;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException;
+
+import java.util.stream.Stream;
+
+import dev.delivercraft.io.CapturingLineWriter;
+import dev.delivercraft.io.LineWriter;
+import dev.delivercraft.io.StubLineReader;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
+import org.junit.jupiter.params.provider.ValueSource;
+
+class PaintCalculatorTest {
+
+    private static final String VALID_LENGTH = "18";
+
+    private static final String VALID_WIDTH = "20";
+
+    private static final String EMPTY_INPUT = "";
+
+    private static final String NON_NUMERIC_INPUT = "abc";
+
+    private static final String ZERO_INPUT = "0";
+
+    private static final String NEGATIVE_INPUT = "-1";
+
+    private static final String SCIENTIFIC_INPUT = "1e3";
+
+    private static final String SHORT_DECIMAL = ".5";
+
+    private static final String LENGTH_PROMPT = "What is the length of the room in feet? ";
+
+    private static final String WIDTH_PROMPT = "What is the width of the room in feet? ";
+
+    @Test
+    void calculatePaint_GivenExampleDimensions_ShouldDisplayGallonsAndArea() {
+        LineWriter lineWriter = new CapturingLineWriter();
+        PaintCalculator calculator = new PaintCalculator(new StubLineReader(VALID_LENGTH, VALID_WIDTH), lineWriter);
+
+        calculator.calculatePaint();
+
+        assertThat(lineWriter).hasToString(LENGTH_PROMPT + WIDTH_PROMPT
+                + "You will need to purchase 2 gallons of paint to cover 360 square feet."
+                + System.lineSeparator());
+    }
+
+    @Test
+    void calculatePaint_GivenSmallCeiling_ShouldUseSingularGallon() {
+        LineWriter lineWriter = new CapturingLineWriter();
+        PaintCalculator calculator = new PaintCalculator(new StubLineReader("10", "10"), lineWriter);
+
+        calculator.calculatePaint();
+
+        assertThat(lineWriter).hasToString(LENGTH_PROMPT + WIDTH_PROMPT
+                + "You will need to purchase 1 gallon of paint to cover 100 square feet."
+                + System.lineSeparator());
+    }
+
+    @Test
+    void calculatePaint_GivenFractionalDimensions_ShouldDisplayExactDecimalArea() {
+        LineWriter lineWriter = new CapturingLineWriter();
+        PaintCalculator calculator = new PaintCalculator(new StubLineReader("10.5", "10.1"), lineWriter);
+
+        calculator.calculatePaint();
+
+        assertThat(lineWriter).hasToString(LENGTH_PROMPT + WIDTH_PROMPT
+                + "You will need to purchase 1 gallon of paint to cover 106.05 square feet."
+                + System.lineSeparator());
+    }
+
+    @Test
+    void calculatePaint_GivenAreaJustOverOneGallon_ShouldRoundGallonsUp() {
+        LineWriter lineWriter = new CapturingLineWriter();
+        PaintCalculator calculator = new PaintCalculator(new StubLineReader("35.1", "10"), lineWriter);
+
+        calculator.calculatePaint();
+
+        assertThat(lineWriter).hasToString(LENGTH_PROMPT + WIDTH_PROMPT
+                + "You will need to purchase 2 gallons of paint to cover 351 square feet."
+                + System.lineSeparator());
+    }
+
+    @ParameterizedTest
+    @MethodSource("invalidInputFlows")
+    void calculatePaint_GivenInvalidInput_ShouldFailFast(String length, String width, String expectedOutput) {
+        LineWriter lineWriter = new CapturingLineWriter();
+        PaintCalculator calculator = new PaintCalculator(new StubLineReader(length, width), lineWriter);
+
+        assertThatIllegalArgumentException()
+                .isThrownBy(calculator::calculatePaint);
+
+        assertThat(lineWriter).hasToString(expectedOutput);
+    }
+
+    private static Stream<Arguments> invalidInputFlows() {
+        return Stream.of(
+                Arguments.of(EMPTY_INPUT, VALID_WIDTH, LENGTH_PROMPT),
+                Arguments.of(null, VALID_WIDTH, LENGTH_PROMPT),
+                Arguments.of(NON_NUMERIC_INPUT, VALID_WIDTH, LENGTH_PROMPT),
+                Arguments.of(ZERO_INPUT, VALID_WIDTH, LENGTH_PROMPT),
+                Arguments.of(NEGATIVE_INPUT, VALID_WIDTH, LENGTH_PROMPT),
+                Arguments.of(SCIENTIFIC_INPUT, VALID_WIDTH, LENGTH_PROMPT),
+                Arguments.of(SHORT_DECIMAL, VALID_WIDTH, LENGTH_PROMPT),
+                Arguments.of(VALID_LENGTH, EMPTY_INPUT, LENGTH_PROMPT + WIDTH_PROMPT),
+                Arguments.of(VALID_LENGTH, null, LENGTH_PROMPT + WIDTH_PROMPT),
+                Arguments.of(VALID_LENGTH, NON_NUMERIC_INPUT, LENGTH_PROMPT + WIDTH_PROMPT),
+                Arguments.of(VALID_LENGTH, ZERO_INPUT, LENGTH_PROMPT + WIDTH_PROMPT),
+                Arguments.of(VALID_LENGTH, NEGATIVE_INPUT, LENGTH_PROMPT + WIDTH_PROMPT),
+                Arguments.of(VALID_LENGTH, SCIENTIFIC_INPUT, LENGTH_PROMPT + WIDTH_PROMPT),
+                Arguments.of(VALID_LENGTH, SHORT_DECIMAL, LENGTH_PROMPT + WIDTH_PROMPT));
+    }
+
+    @ParameterizedTest
+    @ValueSource(strings = {"18", " 18 ", "18.0", "0.5"})
+    void calculatePaint_GivenPlainDecimalInput_ShouldAcceptInput(String input) {
+        LineWriter lineWriter = new CapturingLineWriter();
+        PaintCalculator calculator = new PaintCalculator(new StubLineReader(input, "20"), lineWriter);
+
+        calculator.calculatePaint();
+
+        assertThat(lineWriter.toString()).contains("You will need to purchase");
+    }
+}
diff --git a/paint-calculator/src/test/java/dev/delivercraft/paint/PaintEstimateTest.java b/paint-calculator/src/test/java/dev/delivercraft/paint/PaintEstimateTest.java
diff --git a/paint-calculator/src/test/java/dev/delivercraft/paint/PaintEstimatorTest.java b/paint-calculator/src/test/java/dev/delivercraft/paint/PaintEstimatorTest.java
diff --git a/paint-calculator/src/test/java/dev/delivercraft/paint/RoomDimensionTest.java b/paint-calculator/src/test/java/dev/delivercraft/paint/RoomDimensionTest.java
diff --git a/settings.gradle b/settings.gradle
