Java面試題：Math.round();

public class Test {
    public static void main(String[] args) {
        System.out.println(Math.round(0.5));
        System.out.println(Math.round(-6.6));
        System.out.println(Math.round(-6.4));
        
    }
    
}

返回結果：

源代碼：

源代碼1 

public static int round(float a) {
        int intBits = Float.floatToRawIntBits(a);
        int biasedExp = (intBits & FloatConsts.EXP_BIT_MASK)
                >> (FloatConsts.SIGNIFICAND_WIDTH - 1);
        int shift = (FloatConsts.SIGNIFICAND_WIDTH - 2
                + FloatConsts.EXP_BIAS) - biasedExp;
        if ((shift & -32) == 0) { // shift >= 0 && shift < 32
            int r = ((intBits & FloatConsts.SIGNIF_BIT_MASK)
                    | (FloatConsts.SIGNIF_BIT_MASK + 1));
            if (intBits < 0) {
                r = -r;
            }
           
            return ((r >> shift) + 1) >> 1;
        } else {
            return (int) a;
        }
    }

 源代碼2：

 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
            long r = ((longBits & DoubleConsts.SIGNIF_BIT_MASK)
                    | (DoubleConsts.SIGNIF_BIT_MASK + 1));
            if (longBits < 0) {
                r = -r;
            }
            return ((r >> shift) + 1) >> 1;
        } else {         
            return (long) a;
        }
    }

總結：Math.round()函數有兩種返回值，參數爲float是返回int,參數爲double是返回值爲long，返回值爲離他周圍的整數，距離相同時取較大值。