深入瞭解Java核心類庫–Math類

	public static long round(double a) {
        long longBits = Double.doubleToRawLongBits(a);
        long biasedExp = (longBits & DoubleConsts.EXP_BIT_MASK)
                >> (DoubleConsts.SIGNIFICAND_WIDTH - 1);
        long shift = (DoubleConsts.SIGNIFICAND_WIDTH - 2
                + DoubleConsts.EXP_BIAS) - biasedExp;
        if ((shift & -64) == 0) { // shift >= 0 && shift < 64
            // a is a finite number such that pow(2,-64) <= ulp(a) < 1
            long r = ((longBits & DoubleConsts.SIGNIF_BIT_MASK)
                    | (DoubleConsts.SIGNIF_BIT_MASK + 1));
            if (longBits < 0) {
                r = -r;
            }
            // In the comments below each Java expression evaluates to the value
            // the corresponding mathematical expression:
            // (r) evaluates to a / ulp(a)
            // (r >> shift) evaluates to floor(a * 2)
            // ((r >> shift) + 1) evaluates to floor((a + 1/2) * 2)
            // (((r >> shift) + 1) >> 1) evaluates to floor(a + 1/2)
            return ((r >> shift) + 1) >> 1;
        } else {
            // a is either
            // - a finite number with abs(a) < exp(2,DoubleConsts.SIGNIFICAND_WIDTH-64) < 1/2
            // - a finite number with ulp(a) >= 1 and hence a is a mathematical integer
            // - an infinity or NaN
            return (long) a;
        }
    }
    public static int max(int a, int b) {
        return (a >= b) ? a : b;
    }
	 public static int min(int a, int b) {
        return (a <= b) ? a : b;
    }
    public static int abs(int a) {
        return (a < 0) ? -a : a;
    }

public class Test {
    public static void main(String[] args) {
        System.out.println("≥3.2的最小整數為："+Math.ceil(3.2));//output:4
        System.out.println("≤3.2的最大整數為："+Math.floor(3.2));//output:3
        System.out.println("3.2四舍五入為："+Math.round(3.2));//output:3
        System.out.println("-1,5中較大的數為："+Math.max(-1,5));//output:5
        System.out.println("-1,5中較小的數為："+Math.min(-1,5));//output:-1
        System.out.println("隨機產生[0,5)范圍的數"+Math.random()*5);//output:[0,5)中任意的隨機數
        System.out.println("25的平方根為："+Math.sqrt(25));//output:5
        System.out.println("-9的絕對值為："+Math.abs(-9));//output:9
        System.out.println("2^3的值為："+Math.pow(2,3));//output:8
        System.out.println("以e為基數的對數為："+Math.log(10));
        System.out.println("以10為基數的對數為："+Math.log10(100));//output:2
    }
}