BAEL-821 New class that shows different rounding techniques. Updated POM.

core-java/src/main/java/com/baeldung/maths/Round.java

@@ -0,0 +1,38 @@
+package com.baeldung.maths;
+
+import java.math.BigDecimal;
+import java.math.RoundingMode;
+import java.text.DecimalFormat;
+
+import org.apache.commons.math3.util.Precision;
+import org.decimal4j.util.DoubleRounder;
+
+public class Round {
+    private static final double PI = 3.1415d;
+    
+    public static void main (String args[]) {
+        System.out.println("PI: " + PI);
+        System.out.printf("Value with 3 digits after decimal point %.3f %n", PI);
+        // OUTPUTS: Value with 3 digits after decimal point 3.142
+        DecimalFormat df = new DecimalFormat("###.###");
+        System.out.println(df.format(PI));
+        System.out.println(round(PI, 3));
+        System.out.println(roundOptional(PI, 3));
+        System.out.println(Precision.round(PI, 3));
+        System.out.println(DoubleRounder.round(PI, 3));
+    }
+    
+    public static double round(double value, int places) {
+        if (places < 0) throw new IllegalArgumentException();
+        
+        BigDecimal bd = new BigDecimal(value);
+        bd = bd.setScale(places, RoundingMode.HALF_UP);
+        return bd.doubleValue();
+    }
+    
+    public static double roundOptional(double value, int places) {
+        double scale = Math.pow(10, places);
+        double rounded = Math.round(value * scale) / scale;
+        return rounded;
+    }
+}