BigDecimal in Java

   /**

     * //performance tips

     *         //1 use BigDecimal.valueOf instead of new BigDecimal

     *         //2 use BigDecimal.stripTrailingZeros to avoid unnecessary trailing zeros

     *         //3 use BigDecimal.setScale to avoid unnecessary decimal places

     *         //4 use BigDecimal.compareTo instead of equals to avoid precision loss

     */

    public static void main(String[] args) {

        //1.1 String VS double as parameter of BigDecimal constructor

        BigDecimal num =new BigDecimal(0.1);

        //0.1000000000000000055511151231257827021181583404541015625

        System.out.println(num);

        num =new BigDecimal("0.1");   //0.1

        System.out.println(num);

        //1.2 valueOf VS new BigDecimal

        BigDecimal num3 = BigDecimal.valueOf(0.1);

        System.out.println("BigDecimal.valueOf(0.1): "+num3);//0.1

        //2.1 scale is very important in divide of BigDecimal

        BigDecimal num1 = new BigDecimal("10.0");

        BigDecimal num2 = new BigDecimal("3.0");

        BigDecimal result = num1.divide(num2, 2, RoundingMode.HALF_UP);

        //2.2 java.lang.ArithmeticException: Non-terminating decimal expansion; no exact representable decimal result.

        try {

            result = num1.divide(num2); // throw exception

        } catch (ArithmeticException e) {}

        //3. equals vs compareTo (-1, 0, or 1 as this BigDecimal is numerically less than, equal to, or greater than val.)

        BigDecimal num4 = new BigDecimal("1.0");

        BigDecimal num5 = new BigDecimal("1.00");

        System.out.println(num4.equals(num5)); //false

        System.out.println(num4.compareTo(num5)); //0

        //4.1 scale（小数位数）和 precision（总位数）

        BigDecimal num6 = new BigDecimal("12345678901234567890.1234567890");

        System.out.println(num6.scale()); //10

        System.out.println(num6.precision()); //30

        BigDecimal stripped=num6.stripTrailingZeros();

        System.out.println(stripped.scale());//9

        System.out.println(stripped.precision());//29

        //4.2 setScale

        BigDecimal num7 = new BigDecimal("1234567890.1234567890");

        BigDecimal fixed=num7.setScale(2,RoundingMode.HALF_UP);

        System.out.println(fixed);

        //5.1 BigDecimal is stateless, so it is thread-safe.

        // BigDecimal is immutable, so it is safe to use it as key of ConcurrentHashMap.

        ConcurrentHashMap<BigDecimal, String> map = new ConcurrentHashMap<>();

        // Adding key-value pairs

        map.put(new BigDecimal("10.50"), "Item A");

        map.put(new BigDecimal("25.75"), "Item B");

        map.put(new BigDecimal("15.00"), "Item C");

        // Retrieving values

        String itemA = map.get(new BigDecimal("10.50"));

        System.out.println("Item A: " + itemA);

        // Iterating over the map (not thread-safe if concurrent modifications occur)

        for (BigDecimal key : map.keySet()) {

            System.out.println(key + ": " + map.get(key));

        }

        //5.2 sum of BigDecimal

        BigDecimal sum = new BigDecimal("0.0");

        for (BigDecimal value : map.keySet()) {

            sum = sum.add(value);

            sum.add(value); // error: sum is immutable

        }

        System.out.println("Sum of all values: " + sum);

        //6 which better, BigDecimal or double?

        BigDecimal principal=new BigDecimal("10000");

        BigDecimal rate=new BigDecimal("0.05");

        BigDecimal interest=principal.multiply(rate);

        System.out.println("Interest: "+interest);

        double principal2=10000;

        double rate2 =0.05;

        BigDecimal interest2=BigDecimal.valueOf(principal2*rate2);

        System.out.println("Interest2: "+interest2);

    }