Java学习笔记:关于Java double类型相加问题

new BigDecimal(Double.toString(double)).add(new BigDecimal(Double.toString(double));

    /**
     * @param b1
     *            BigDecimal
     * @param v2
     *            double
     * @return BigDecimal
     * */
    public BigDecimal add(BigDecimal b1, double v2) {
        // BigDecimal b1=new BigDecimal(Double.toString(v1));
        BigDecimal b2 = new BigDecimal(Double.toString(v2));
        return b1.add(b2);
    }

    /**
     * @param b1
     *           double
     * @param v2
     *            double
     * @return BigDecimal
     * */
    public BigDecimal add(double v1, double v2) {
         BigDecimal b1=new BigDecimal(Double.toString(v1));
        BigDecimal b2 = new BigDecimal(Double.toString(v2));
        return b1.add(b2);
    }

    /**
     * @param b1
     *           double
     * @param v2
     *            double
     * @return double
     * */
    public double add(double v1, double v2) {
         BigDecimal b1=new BigDecimal(Double.toString(v1));
        BigDecimal b2 = new BigDecimal(Double.toString(v2));
        return b1.add(b2).doubleValue();
    }

public class MathDemo {

    /**
     * @param args
     */
    public static void main(String[] args) {
        System.err.println("普通 "+ addNormal(12353.21,21334.24,154435.03));
        System.err.println("strictfp "+addDouble(12353.21,21334.24,154435.03));
        System.err.println("BigDEcimel: "+add(12353.21,21334.24,154435.03));

    }

    public static double addNormal(double... v1) {
        double res = 0;
        for (int i = 0; i < v1.length; i++) {
            res += v1[i];
        }
        return res;
    }

    public static strictfp double addDouble(double... v) {
        double res = 0;
        for (int i = 0; i < v.length; i++) {
            res += v[i];
        }
        return res;
    }

    /**
     * @param b1
     *            double
     * @param v2
     *            double
     * @return double
     */
    public static double add(double... v) {
        BigDecimal b  = new BigDecimal(Double.toString(v[0]));
        for (int i = 1; i < v.length; i++) {
            BigDecimal b2 = new BigDecimal(Double.toString(v[i]));
            b=b.add(b2);
        }
        return b.doubleValue();
    }
}

//使用double类型创建BigDecimal
  public BigDecimal(double val) {
        if (Double.isInfinite(val) || Double.isNaN(val))
            throw new NumberFormatException("Infinite or NaN");

        // Translate the double into sign, exponent and significand, according
        // to the formulae in JLS, Section 20.10.22.
        long valBits = Double.doubleToLongBits(val);
        int sign = ((valBits >> 63)==0 ? 1 : -1);
        int exponent = (int) ((valBits >> 52) & 0x7ffL);
        long significand = (exponent==0 ? (valBits & ((1L<<52) - 1)) << 1
                            : (valBits & ((1L<<52) - 1)) | (1L<<52));
        exponent -= 1075;
        // At this point, val == sign * significand * 2**exponent.

        /*
         * Special case zero to supress nonterminating normalization
         * and bogus scale calculation.
         */
        if (significand == 0) {
            intVal = BigInteger.ZERO;
            intCompact = 0;
            precision = 1;
            return;
        }

        // Normalize
        while((significand & 1) == 0) {    //  i.e., significand is even
            significand >>= 1;
            exponent++;
        }

        // Calculate intVal and scale
        long s = sign * significand;
        BigInteger b;
        if (exponent < 0) {
            b = BigInteger.valueOf(5).pow(-exponent).multiply(s);
            scale = -exponent;
        } else if (exponent > 0) {
            b = BigInteger.valueOf(2).pow(exponent).multiply(s);
        } else {
            b = BigInteger.valueOf(s);
        }
        intCompact = compactValFor(b);
        intVal = (intCompact != INFLATED) ? null : b;
    }

Double double1 = new Double(5.556);    // 以 double 类型的变量作为参数创建 Double 对象
Double double2 = new Double("5.486");       // 以 String 类型的变量作为参数创建 Double 对象

String str = "56.7809";
double num = Double.parseDouble(str);    // 将字符串转换为 double 类型的数值
double d = 56.7809;
String s = Double.toString(d);    // 将double类型的数值转换为字符串