How to convert hex string to float in Java?

Question

How to convert hexadecimal string to single precision floating point in Java?

For example, how to implement:

float f = HexStringToFloat("BF800000"); // f should now contain -1.0

I ask this because I have tried:

float f = (float)(-1.0);
String s = String.format("%08x", Float.floatToRawIntBits(f));
f = Float.intBitsToFloat(Integer.valueOf(s,16).intValue());

But I get the following exception:

java.lang.NumberFormatException: For input string: "bf800000"

John Meagher · Accepted Answer · 2009-07-02T00:26:48.890

22

public class Test {
  public static void main (String[] args) {

        String myString = "BF800000";
        Long i = Long.parseLong(myString, 16);
        Float f = Float.intBitsToFloat(i.intValue());
        System.out.println(f);
        System.out.println(Integer.toHexString(Float.floatToIntBits(f)));
  }
}

edited Jul 02 '09 at 00:26

answered Jul 02 '09 at 00:04

John Meagher

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I get: java.lang.NumberFormatException: For input string: "BF800000" – apalopohapa Jul 02 '09 at 00:09
When testing: Float.intBitsToFloat(Integer.valueOf("BF800000",16).intValue()); I get the exception: java.lang.NumberFormatException: For input string: "BF800000" – apalopohapa Jul 02 '09 at 00:10
It's overflowing an int. Switching it to Long.valueOf(myString, 16) doesn't throw the exception, but results in -1.0 instead of 10.0. Are you sure 10.0 is the correct result? – John Meagher Jul 02 '09 at 00:17
that number is too big maybe? try using Long instead of integer. – Victor Jul 02 '09 at 00:17
i'm with john here, i'm getting -1.0 not 10.0 – Victor Jul 02 '09 at 00:18
Confirmed the listed answer of 10.0 is not correct. The sample value is -1.0. Tested with above code and it works (now that it's Long instead of Integer). – John Meagher Jul 02 '09 at 00:22
Also, if my memory is working right, the top bit in an IEEE-754 float is the sign bit so the sample would have to be a negative number. – John Meagher Jul 02 '09 at 00:22
Also, 10.0 converts to "41200000" – John Meagher Jul 02 '09 at 00:24
Hi, yes, "BF800000" is -1.0, and using Long removes the exception. Thanks! – apalopohapa Jul 02 '09 at 00:26

score 2 · Answer 2 · answered Jul 02 '09 at 00:05

2

You need to convert the hex value to an int (left as an exercise) and then use Float.intBitsToFloat(int)

answered Jul 02 '09 at 00:05

Jherico

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How to convert hex string to float in Java?

2 Answers2

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