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/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

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+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

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+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);
+    }
+
+}