BAEL-7226: Code for the improvements of the Percentages article. (#15352)

* BAEL-7226: Code for the improvements of the Percentages article.

* BAEL-7226: Rename Test to follow the convention

core-java-modules/core-java-lang-math/pom.xml

@@ -5,6 +5,14 @@
     <modelVersion>4.0.0</modelVersion>
     <artifactId>core-java-lang-math</artifactId>
     <name>core-java-lang-math</name>
+    <dependencies>
+        <dependency>
+            <groupId>org.projectlombok</groupId>
+            <artifactId>lombok</artifactId>
+            <version>1.18.24</version>
+            <scope>compile</scope>
+        </dependency>
+    </dependencies>
     <packaging>jar</packaging>
 
     <parent>

core-java-modules/core-java-lang-math/src/main/java/com/baeldung/algorithms/percentage/BigDecimalPercentageCalculator.java

@@ -0,0 +1,20 @@
+package com.baeldung.algorithms.percentage;
+
+import lombok.experimental.ExtensionMethod;
+import java.math.BigDecimal;
+import java.util.Scanner;
+
+@ExtensionMethod(FastBigDecimalPercentage.class)
+public class BigDecimalPercentageCalculator {
+    public static void main(String[] args) {
+
+        Scanner in = new Scanner(System.in);
+        System.out.println("Enter obtained marks:");
+        BigDecimal obtained = new BigDecimal(in.nextDouble());
+        System.out.println("Enter total marks:");
+        BigDecimal total = new BigDecimal(in.nextDouble());
+
+        System.out.println("Percentage obtained :"+ obtained.toPercentageOf(total));
+    }
+
+}

core-java-modules/core-java-lang-math/src/main/java/com/baeldung/algorithms/percentage/BigDecimalPercentages.java

@@ -0,0 +1,18 @@
+package com.baeldung.algorithms.percentage;
+
+
+import java.math.BigDecimal;
+import java.math.RoundingMode;
+
+public class BigDecimalPercentages {
+
+    private static final BigDecimal ONE_HUNDRED = new BigDecimal("100");
+
+    public BigDecimal toPercentageOf(BigDecimal value, BigDecimal total) {
+        return value.divide(total, 4, RoundingMode.HALF_UP).multiply(ONE_HUNDRED);
+    }
+
+    public BigDecimal percentOf(BigDecimal percentage, BigDecimal total) {
+        return percentage.multiply(total).divide(ONE_HUNDRED, 2, RoundingMode.HALF_UP);
+    }
+}

core-java-modules/core-java-lang-math/src/main/java/com/baeldung/algorithms/percentage/FastBigDecimalPercentage.java

@@ -0,0 +1,16 @@
+package com.baeldung.algorithms.percentage;
+
+import java.math.BigDecimal;
+import java.math.RoundingMode;
+
+public class FastBigDecimalPercentage {
+
+    public static BigDecimal toPercentageOf(BigDecimal value, BigDecimal total) {
+        return value.divide(total, 4, RoundingMode.HALF_UP).scaleByPowerOfTen(2);
+    }
+
+    public static BigDecimal percentOf(BigDecimal percentage, BigDecimal total) {
+        return percentage.multiply(total).scaleByPowerOfTen(-2);
+    }
+
+}

core-java-modules/core-java-lang-math/src/test/java/com/baeldung/algorithms/percentage/BigDecimalPercentageUnitTest.java

@@ -0,0 +1,27 @@
+package com.baeldung.algorithms.percentage;
+
+import org.hamcrest.number.BigDecimalCloseTo;
+import org.junit.Assert;
+import org.junit.Test;
+
+import java.math.BigDecimal;
+
+public class BigDecimalPercentageUnitTest {
+    private BigDecimalPercentages pc = new BigDecimalPercentages();
+
+
+    @Test
+    public void shouldConvertToPercentageOfTotal(){
+        BigDecimalCloseTo expected = new BigDecimalCloseTo(new BigDecimal(5.05), new BigDecimal(0.001));
+        Assert.assertTrue("Result not as expected",expected.matchesSafely(
+                pc.toPercentageOf(new BigDecimal(50.5),new BigDecimal(1000))));
+    }
+
+    @Test
+    public void shouldCalculatePercentageOfTotal(){
+        BigDecimalCloseTo expected = new BigDecimalCloseTo(new BigDecimal(31.40), new BigDecimal(0.001));
+        Assert.assertTrue("Result not as expected",expected.matchesSafely(
+                pc.percentOf(new BigDecimal(3.14),new BigDecimal(1000))));
+    }
+
+}

core-java-modules/core-java-lang-math/src/test/java/com/baeldung/algorithms/percentage/FastBigDecimalPercentageUnitTest.java

@@ -0,0 +1,27 @@
+package com.baeldung.algorithms.percentage;
+
+import org.hamcrest.number.BigDecimalCloseTo;
+import org.junit.Assert;
+import org.junit.Test;
+
+import java.math.BigDecimal;
+
+public class FastBigDecimalPercentageUnitTest {
+    private FastBigDecimalPercentage pc = new FastBigDecimalPercentage();
+
+
+    @Test
+    public void shouldConvertToPercentageOfTotal(){
+        BigDecimalCloseTo expected = new BigDecimalCloseTo(new BigDecimal(5.05), new BigDecimal(0.001));
+        Assert.assertTrue("Result not as expected",expected.matchesSafely(
+                pc.toPercentageOf(new BigDecimal(50.5),new BigDecimal(1000))));
+    }
+
+    @Test
+    public void shouldCalculatePercentageOfTotal(){
+        BigDecimalCloseTo expected = new BigDecimalCloseTo(new BigDecimal(31.40), new BigDecimal(0.001));
+        Assert.assertTrue("Result not as expected",expected.matchesSafely(
+                pc.percentOf(new BigDecimal(3.14),new BigDecimal(1000))));
+    }
+
+}