int array to byte array

[Drew Lane]

What is the best way to convert an int array to a byte array?

Can I just cast it?

Maybe I should try System.arrayCopy or a ByteArrayOutputStream?

Thanks,

Drew

[Ernest Friedman-Hill]

A straightforward "for" loop that assigns the elements one at a time, with a cast, is the only sensible way to do it.

[Joe Ess]

You can't cast the array reference even though you can cast the array elements. I'm a fan of using System.arrayCopy to accomplish this task.

[Ernest Friedman-Hill]

Originally posted by Joe Ess:
I'm a fan of using System.arrayCopy to accomplish this task.

'Twould be nice, but it doesn't actually work:

int[] ia = { 1, 2, 3};
byte[] ba = new byte[3];
System.arraycopy(ia, 0, ba, 0, 3);

gives

Exception in thread "main" java.lang.ArrayStoreException
at java.lang.System.arraycopy(Native Method)
at Foo.main(Foo.java:7)

The Javadoc says that you can only copy across different-type arrays if the assignment across the two types can be made by "assignment conversion" -- i.e., without a cast. So you could do it in the other direction (byte[] to int[]) but not int[] to byte[].

[Drew Lane]

Originally posted by Ernest Friedman-Hill:
A straightforward "for" loop that assigns the elements one at a time, with a cast, is the only sensible way to do it.

Won't this result in a loss of information since an int is larger than a byte?

Drew

[Ernest Friedman-Hill]

Originally posted by Drew Lane:

Won't this result in a loss of information since an int is larger than a byte?

Yes, absolutely, it would, but I assumed you knew that. Were you thinking of converting each int to four bytes, maybe? What did you want to do with the result?

[Drew Lane]

Originally posted by Ernest Friedman-Hill:


Yes, absolutely, it would, but I assumed you knew that. Were you thinking of converting each int to four bytes, maybe? What did you want to do with the result?

Yes, four bytes would be good.

Then I'm thinking of using the resulting byte array in a ByteArrayInputStream.

Drew
[ May 29, 2004: Message edited by: Drew Lane ]

[Jim Yingst]

If you want to convert each int to four bytes and thus ensure no lost info, you can use a DataOutputStream wrapped around a ByteArrayOutputStream. Loop through each int in the array and use writeInt() - it will be writtenas four bytes, high byte first. When done, use toByteArray() to get the complete array. If / when you want to read the values back into ints later, just use a DataInputStream, which has a readInt() method.