Fix Format

java-numbers/src/main/java/com/baeldung/maths/BigDecimalDemo.java

@@ -0,0 +1,29 @@
+package com.baeldung.maths;
+
+import java.math.BigDecimal;
+import java.math.RoundingMode;
+
+public class BigDecimalDemo {
+
+    /** Calculate total amount to be paid for an item rounded to cents..
+     * @param quantity
+     * @param unitPrice
+     * @param discountRate
+     * @param taxRate
+     * @return
+     */
+    public static BigDecimal calculateTotalAmount(BigDecimal quantity,
+        BigDecimal unitPrice, BigDecimal discountRate, BigDecimal taxRate) {
+        BigDecimal amount = quantity.multiply(unitPrice);
+        BigDecimal discount = amount.multiply(discountRate);
+        BigDecimal discountedAmount = amount.subtract(discount);
+        BigDecimal tax = discountedAmount.multiply(taxRate);
+        BigDecimal total = discountedAmount.add(tax);
+
+        // round to 2 decimal places using HALF_EVEN
+        BigDecimal roundedTotal = total.setScale(2, RoundingMode.HALF_EVEN);
+
+        return roundedTotal;
+    }
+
+}

java-numbers/src/main/java/com/baeldung/maths/FloatingPointArithmetic.java

@@ -0,0 +1,51 @@
+package com.baeldung.maths;
+
+import java.math.BigDecimal;
+
+public class FloatingPointArithmetic {
+    public static void main(String[] args) {
+        
+        double a = 13.22;
+        double b = 4.88;
+        double c = 21.45;
+        
+        System.out.println("a =         " + a);
+        System.out.println("b =         " + b);
+        System.out.println("c =         " + c);
+        
+        double sum_ab = a + b;
+        System.out.println("a + b =     " + sum_ab);
+        
+        double abc =  a + b + c;
+        System.out.println("a + b + c = " + abc);
+        
+        double ab_c = sum_ab + c;
+        System.out.println("ab + c =    " + ab_c);
+        
+        double sum_ac = a + c;
+        System.out.println("a + c =     " + sum_ac);
+        
+        double acb = a + c + b;
+        System.out.println("a + c + b = " + acb);
+        
+        double ac_b = sum_ac + b;
+        System.out.println("ac + b =    " + ac_b);
+        
+        double ab = 18.1;
+        double ac = 34.67;
+        double sum_ab_c = ab + c;
+        double sum_ac_b = ac + b;
+        System.out.println("ab + c =    " + sum_ab_c);
+        System.out.println("ac + b =    " + sum_ac_b);
+        
+        BigDecimal d = new BigDecimal(String.valueOf(a));
+        BigDecimal e = new BigDecimal(String.valueOf(b));
+        BigDecimal f = new BigDecimal(String.valueOf(c));
+        
+        BigDecimal def = d.add(e).add(f);
+        BigDecimal dfe = d.add(f).add(e);
+        
+        System.out.println("d + e + f = " + def);
+        System.out.println("d + f + e = " + dfe);
+    }
+}

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

@@ -0,0 +1,47 @@
+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(roundNotPrecise(PI, 3));
+        System.out.println(roundAvoid(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(Double.toString(value));
+        bd = bd.setScale(places, RoundingMode.HALF_UP);
+        return bd.doubleValue();
+    }
+    
+    public static double roundNotPrecise(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 roundAvoid(double value, int places) {
+        double scale = Math.pow(10, places);
+        double rounded = Math.round(value * scale) / scale;
+        return rounded;
+    }
+}