getting wrong values while reading Double from binary file in java

Question

RandomAccessFile in = new RandomAccessFile("BOT.grd", "r");
in.seek(28);
double xll=in.readDouble();

The above is the code i am using to read double data which is present from 29 to 36 byte location.The value present is 500 but i am getting 2.088E-317

There's something wrong in either the code reading the file or the code writing the file. That's all we can say without more details/code/examples. Please see tinyurl.com/so-hints — Jon Skeet
– Jon Skeet, Commented Nov 7, 2011 at 14:30
Can you give more specifics about how you are reading and writing the file? Given that you are using RandomAccessFile, I guess you are not using serialization. So how are you writing and then reading the data? How about a code snippet for each? — Gray
– Gray, Commented Nov 7, 2011 at 15:06
I had give my code above. I was unable to read double values its working fine with integer values — raviteja
– raviteja, Commented Nov 7, 2011 at 16:12

Jörn Horstmann · Accepted Answer · 2011-11-07 17:06:15Z

1

It seems this file is stored in a different Endianness than the one java uses. The bytes probably need to be reversed before converting to double, you could try the following code to read the value:

long   l = in.readLong();
double d = Double.longBitsToDouble(Long.reverseBytes(l));

Here is an example that illustrates the problem:

double d = 500.0;

long l1 = Double.doubleToLongBits(d);
long l2 = Long.reverseBytes(l1);

System.out.println(Double.longBitsToDouble(l1));
System.out.println(Double.longBitsToDouble(l2));

Output:

500.0
2.088356E-317

answered Nov 7, 2011 at 17:06

Jörn Horstmann

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1 Comment

Jörn Horstmann Over a year ago

@raviteja is this still not working for you? If so, we would need some more information or examples of this file format. But as you accepted this answer, I would assume it solved your problem.

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