Conversion from Long to Double in Java

Question

Is there any way to convert a Long data type to Double or double?

For example, I need to convert 15552451L to a double data type.

Solution 1

You could simply do :

double d = (double)15552451L;

Or you could get double from Long object as :

Long l = new Long(15552451L);
double d = l.doubleValue();

Solution 2

Simple casting?

double d = (double)15552451L;

Solution 3

As already mentioned, you can simply cast long to double. But be careful with long to double conversion because long to double is a narrowing conversion in java.

Conversion from type double to type long requires a nontrivial translation from a 64-bit floating-point value to the 64-bit integer representation. Depending on the actual run-time value, information may be lost.

e.g. following program will print 1 not 0

    long number = 499999999000000001L;
    double converted = (double) number;
    System.out.println( number - (long) converted);

Solution 4

Are you looking for the binary conversion?

double result = Double.longBitsToDouble(15552451L);

This will give you the double with the same bit pattern as the provided long.

Binary or hexadecimal literals will come in handy, here. Here are some examples.

double nan = Double.longBitsToDouble(0xfff0000000000001L);
double positiveInfinity = Double.longBitsToDouble(0x7ff0000000000000L);
double negativeInfinity = Double.longBitsToDouble(0xfff0000000000000L);

(See Double.longBitsToDouble(long))

You also can get the long back with

long bits = Double.doubleToRawLongBits(Double.NaN);

(See Double.doubleToRawLongBits(double))

Solution 5

Long i = 1000000;
String s = i + "";
Double d = Double.parseDouble(s);
Float f = Float.parseFloat(s);

This way we can convert Long type to Double or Float or Int without any problem because it's easy to convert string value to Double or Float or Int.

View more solutions

Comments

[Jon Freedman]

And if its a literal just 15552451d

[Joe Kearney]

Don't need any string parsing there: Long.valueOf(15552451L).doubleValue() if you want to go via Long. Note this is the same, internally, as the cast from a double, except that you're doing some auto/unboxing.

[crusam]

I even think a cast is not necessary, you can create a double with a long value like this: "double d = 1234L;".

[Jim Brissom]

Probably not - but the question is basic enough to warrant the introduction of a concept like casting.

[Joe Kearney]

I did. Parsing a string to do this (now edited out of the answer) will degrade performance by many orders of magnitude. Boxing is less expensive but still worth avoiding, especially in cases like this (using new) where it can't be elided away.

[ams]

I think the example was supposed to show that you can get from Long -> double. How the Long was initialised doesn't seem that important..

[Joe Kearney]

Granted the example in the answer looks more reasonable now having been edited. I maintain that conversion from a value to a double via a String is not good practice. I would have thought that to be fairly uncontroversial.

[YoK]

My 2nd example is just showing how to get double value , if you have Long object. If you just had number , why would you assign long value to double by casting ? You could very well assign value directly as double.

[YoK]

@jjk If you look at question , it does mention converting from Long (object) to double. I don't understand what is your stand on this and what's the controversy.

[Teemu Leisti]

I guess that a long date would be something like "Tuesday, 19 September 24893243092333".

[Jiri Kremser]

This does something else, see the jdoc (docs.oracle.com/javase/6/docs/api/java/lang/…)

[pvorb]

Yes. But he did not specify how he wants to convert long to double (I think casting is one of the first things you learn when using Java) nor did he accept any answer. Maybe he wants to get a double with the same bit pattern as the long value. Well, I don't know. So I just gave the answer.

[pvorb]

I added additional information, so the answer is more valuable.

[cutemachine]

You do not need to cast explicitly. It just works: double d = 15552451L;

[abarisone]

It's always better to add an explanation to the code you're posting as an answer, so that it will helps visitors understand why this is a good answer.

[vpzomtrrfrt]

Your link says the opposite, that double to long is a narrowing conversion, while long to double is widening

[Antonio]

Formally, long->double is not narrowing, but this conversion can still loose precision: "A widening conversion of an int or a long value to float, or of a long value to double, may result in loss of precision - that is, the result may lose some of the least significant bits of the value. In this case, the resulting floating-point value will be a correctly rounded version of the integer value, using IEEE 754 round-to-nearest mode (§4.2.4). " docs.oracle.com/javase/specs/jls/se7/html/jls-5.html#jls-5.1‌​.2

[Antonio]

(continued) (long) converted is not a good illustration of the answer as double -> long is a narrowing conversion and number - (long) converted should not always give 0 by definition docs.oracle.com/javase/specs/jls/se7/html/jls-5.html#jls-5.1‌​.3