Converting big decimal to double without exponential format

问题

I'm doing calculations on High decimal precision BigDecimal objects.

I'm using a third party library that requires the parameter in double. When I try to convert this to double i get the values in exponential format instead of decimals .

BigDecimal 0.000035000000000
Double 3.5E-5

BigDecimal bd; 
BigDecimal(0.0000349999999995631583260546904057264328002929687500);
bd= bd.setScale(15,BigDecimal.ROUND_CEILING);

Log.i("bd","bd "+bd.toPlainString());
Log.i("bd","double"+bd.doubleValue());

I have found various ways of converting this 3.5E-5 value as correct decimal in points but in String format only . Whereas I need the value in double

Able to get without exponential in String object But not in double

  DecimalFormat df = new DecimalFormat("#");
        df.setMaximumFractionDigits(16);
       String test=df.format(bd,doubleValue());
        System.out.println("op2 "+test);
        Double test1=Double.parseDouble(test);
        System.out.println("op2 "+test1);

OUTPUT op2 .000035 op2 3.5E-5

I'm struggling since since days to find a solution as I have no control over 3rd party library that requires the value to be in double

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My question is different then these links, I do not want the double as string without exponential instead I want it in double format only.

EDIT

If the double value passed is in exponential format, the NDK based libary will further do calculations on this object, which will result inmore decimal points and larger Exponential value. So, I want to pass a simple double without E

回答1:

You seem to be confusing a double, a 64 bit value where different bits have a different meaning, with its string representation.

Let's take a value of 0.015625. Internally, the double is represented as 64 bits (I don't know right now which combination of bits, but that is irrelevant anyway).

But the string representation depends on the format settings of the library you are using. Note that the representations 0.015625 and 1.5625E-2 represent the exact same double value. The double is not stored as a string, it does not contain a . or an E, just a number of bits. The combination of these bits form its real value, and it is the same, no matter how you represent it as a string. If you have a different format setting, the result can just as well be 1.56E-2. This just means that the code that converts the internal bit combination of the double to a string does some rounding.

So, to obtain a double from a BigDecimal, simply use bd.doubleValue(). There is no need to use an intermediate string representation, and it can even be detrimental to do so, because if the string representation performs some rounding, you don't get the best approximation of the value in the BigDecimal.

So again, bd.doubleValue() is the only correct way to do this. This does not return a specific format, it simply returns the double that is closest to the value in the BigDecimal.

And again, do not confuse the double type with how it is represented as a string. These are different things. A double is a double is a double, and that is not stored as a string, exponential or plain or rounded or whatever.

Actually, BigDecimal.toString() and BigDecimal.toPlainString() also return different string representations of the same BigDecimal. AFAIK, there is even a third string conversion function, toEngineeringString(), which gives you yet another string representation of the same BigDecimal. This is similar for double: different output routines with different arguments return different strings for the exact same value.

回答2:

use this: amount=value to be converted to double from string

    double dd = new BigDecimal(amount).doubleValue();
    String val = String.format("%.4f", dd);
    BigDecimal bd = BigDecimal.valueOf(Double.valueOf(val));
    Double d=bd.doubleValue() ;
    DecimalFormat formatter = new DecimalFormat("0.0000");
    System.out.println("doubleValue= " + formatter .format(d));

来源：https://stackoverflow.com/questions/39138396/converting-big-decimal-to-double-without-exponential-format

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java

android

double

bigdecimal