Different results are obtained while rounding decimals

double radius = 5;
double area = Math.PI * Math.pow(radius, 2);            
// System.out.println(area);

BigDe开发者_高级运维cimal bd = new BigDecimal(area).setScale(2, HALF_UP);
// BigDecimal bd = new BigDecimal(area).setScale(2, ROUND_HALF_UP);
System.out.println(bd.toString());

The above output gets printed as 78.54, but if I perform the same operation via the calculator (windows calc interface) the output comes out as 78.57 (i.e. 22/7 * 25).

Why is there an inconsistency

Are you using 22/7 as an approximate value for PI? Because 22/7 is 3.142857142857... where PI is approximately 3.14159.... This explains your rounding inconsistencies.

The approximation of PI that is used in the JVM is documented here. According to the JavaDoc, it is:

The double value that is closer than any other to pi

22/7 is approximation to PI , Its not exact and so the result

Almost completely off-topic (and its javascript). But its still a fun answer for actually visibly seeing PI being calculated.

This method is obviously super-super-slow at calculating PI...but is kinda fun to watch.

(function (t) {
    (function () {
        var a = 0,
            b = 1,
            d = 4,
            c = ~1e9;
        (function p() {
            if (!t) {
                return;
            }
            b -= 2;
            a -= d / b;
            d = -d;
            if (++c % 2000 === 0) {
                t.innerHTML = a;
                setTimeout(p, 13);
            } else {
                if (c) {
                    p();
                } else {
                    t.innerHTML = a;
                }
            }
        }());
    }());
}(document.getElementById("someplace-to-hold-the-calculation")))

Philippe Leybaert set up a JSBin for it.