lab2

build.gradle

@@ -3,7 +3,7 @@ plugins {
 }
 
 group = 'ru.lionarius'
-version = '1-LAB'
+version = '2-LAB'
 
 repositories {
     mavenCentral()

src/main/java/ru/lionarius/IntegralCalculator.java

@@ -0,0 +1,75 @@
+package ru.lionarius;
+
+import java.util.function.Function;
+
+/**
+ * A class that provides a numerical method to calculate definite integrals of a given function.
+ * The integration is performed using the trapezoidal rule, with a specified accuracy.
+ */
+public class IntegralCalculator {
+
+    /**
+     * The accuracy level for the integration process.
+     * A smaller value results in higher accuracy but more computation time.
+     */
+    private final double accuracy;
+
+    /**
+     * Constructs an {@link IntegralCalculator} with the specified accuracy.
+     *
+     * @param accuracy The desired accuracy for the integral calculation
+     * @throws IllegalArgumentException if the accuracy is less than or equal to zero.
+     */
+    public IntegralCalculator(double accuracy) {
+        if (accuracy <= 0.0)
+            throw new IllegalArgumentException("accuracy must be a positive number");
+
+        this.accuracy = accuracy;
+    }
+
+    /**
+     * Returns the accuracy level used for the integration calculation.
+     *
+     * @return The accuracy level as a double.
+     */
+    public double getAccuracy() {
+        return this.accuracy;
+    }
+
+    /**
+     * Calculates the definite integral of the specified function over a given interval
+     * using the trapezoidal rule.
+     *
+     * @param function   The function to integrate.
+     * @param lowerBound The lower bound of the integration interval.
+     * @param upperBound The upper bound of the integration interval.
+     * @return The estimated value of the definite integral.
+     */
+    public double calculate(Function<Double, Double> function, double lowerBound, double upperBound) {
+        if (lowerBound == upperBound)
+            return 0.0;
+
+        var invert = false;
+        if (lowerBound > upperBound) {
+            invert = true;
+
+            var temp = lowerBound;
+            lowerBound = upperBound;
+            upperBound = temp;
+        }
+
+        var n = (long) Math.ceil((upperBound - lowerBound) / this.accuracy);
+        var h = (upperBound - lowerBound) / n;
+
+        var sum = (function.apply(lowerBound) + function.apply(upperBound)) / 2;
+        for (var i = 1L; i < n; i++)
+            sum += function.apply(lowerBound + h * i);
+
+        sum *= h;
+
+        if (invert)
+            sum = -sum;
+
+        return sum;
+    }
+}

src/main/java/ru/lionarius/Main.java

@@ -1,7 +1,24 @@
 package ru.lionarius;
 
+import java.util.function.Function;
+
 public class Main {
     public static void main(String[] args) {
-        System.out.println("Hello world!");
+        Function<Double, Double> function = x -> Math.sin(x) * x;
+        var lowerBound = 0.0;
+        var upperBound = 1.0;
+        double[] accuracies = {0.001, 0.00001, 0.0000001, 0.000000001};
+
+        for (var accuracy : accuracies) {
+            var calculator = new IntegralCalculator(accuracy);
+
+            var startTime = System.nanoTime();
+
+            var value = calculator.calculate(function, lowerBound, upperBound);
+
+            var totalTime = System.nanoTime() - startTime;
+
+            System.out.printf("Calculated value: %.15f | Accuracy: %e | Time: %.9fms%n", value, accuracy, totalTime / 1_000_000.0);
+        }
     }
 }

src/test/java/IntegralCalculatorTests.java

@@ -0,0 +1,53 @@
+import org.junit.jupiter.api.Test;
+import ru.lionarius.IntegralCalculator;
+
+import java.util.function.Function;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class IntegralCalculatorTests {
+
+    private static void assertIntegral(final double expected, final IntegralCalculator calculator, final Function<Double, Double> function, final double lowerBound, final double upperBound) {
+        var value = calculator.calculate(function, lowerBound, upperBound);
+
+        assertEquals(value, expected, calculator.getAccuracy());
+    }
+
+    @Test
+    void accuracyValidRange() {
+        assertThrowsExactly(IllegalArgumentException.class, () -> new IntegralCalculator(0.0));
+        assertThrowsExactly(IllegalArgumentException.class, () -> new IntegralCalculator(-0.0));
+        assertThrowsExactly(IllegalArgumentException.class, () -> new IntegralCalculator(-1.0));
+
+        assertDoesNotThrow(() -> new IntegralCalculator(Double.MIN_VALUE));
+    }
+
+    @Test
+    void accuracy_SinXX() {
+        final var actualValue = 0.30116867893975678925156571418732239589025264018044883800265445461081000961676790443;
+
+        final Function<Double, Double> function = x -> Math.sin(x) * x;
+        final var lowerBound = 0.0;
+        final var upperBound = 1.0;
+        final double[] accuracies = {0.001, 0.00001, 0.0000001};
+
+        for (var accuracy : accuracies) {
+            var calculator = new IntegralCalculator(accuracy);
+
+            assertIntegral(actualValue, calculator, function, lowerBound, upperBound);
+        }
+    }
+
+    @Test
+    void bounds_X() {
+        final var calculator = new IntegralCalculator(0.1);
+
+        final Function<Double, Double> function = x -> x;
+        final var lowerBound = 0.0;
+        final var upperBound = 1.0;
+
+        assertIntegral(0.5, calculator, function, lowerBound, upperBound);
+        assertIntegral(-0.5, calculator, function, upperBound, lowerBound);
+        assertIntegral(0.0, calculator, function, lowerBound, lowerBound);
+    }
+}