I want to convert an int array to a hex string. I am unsure if I am doing this correctly.
I create an int[] in another class and get it with via msg.obj. I am getting some values in Hex but am unsure if they are correct.
int[] readBuf = (int[]) msg.obj; //int array is in another class
StringBuffer output=new StringBuffer();
for (int a:readBuf) {
int val1 = a & 0xff;
output.append(Integer.toHexString(val1));
}
dataView.setText(output);
Assuming I understand your intention, there are two problems with the code:
int val1 = a & 0xff;
You're taking only the last byte of your int. If you want to convert the whole integer, remove the &0xff.
You want to makes sure that the output of Integer.toHexString is always padded with zeroes in front so it's length is always 8 characters (since every byte of the 4 byte long int requres 2 characters). Otherwise both array {1,2,3} and the array {291} will give you the same string - 123.
here's a quick and dirty working code example
public static String byteToUnsignedHex(int i) {
String hex = Integer.toHexString(i);
while(hex.length() < 8){
hex = "0" + hex;
}
return hex;
}
public static String intArrToHex(int[] arr) {
StringBuilder builder = new StringBuilder(arr.length * 8);
for (int b : arr) {
builder.append(byteToUnsignedHex(b));
}
return builder.toString();
}
public static void main(String[] args){
System.out.println(intArrToHex(new int[]{1,2,3}));
System.out.println(intArrToHex(new int[]{291}));
System.out.println(intArrToHex(new int[]{0xFFFFFFFF}));
}
Output:
000000010000000200000003
00000123
ffffffff
@Malt's answer definitely highlights the problem with your code: that it doesn't 0-pad the int hex values; and that you mask the int to only take the last 8 bits using a & 0xff. Your original question implies you are only after the last byte in each int, but it really isn't clear.
You say you get results every second from your remote object. On a slow machine with large arrays it is possible that it could take a significant number of milliseconds to convert a long int[] to a hex string using your method using your (or rather Malt's corrected version of your) method.
A much faster method would be to get each 4-bit nibble from each int using bit shifting, and get the appropriate hex character from a static hex lookup array (note this does base-16 encoding, you would get shorter strings from something like base-64 encoding):
public class AltConverter {
final protected static char[] encoding = "0123456789ABCDEF".toCharArray();
public String convertToString(int[] arr) {
char[] encodedChars = new char[arr.length * 4 * 2];
for (int i = 0; i < arr.length; i++) {
int v = arr[i];
int idx = i * 4 * 2;
for (int j = 0; j < 8; j++) {
encodedChars[idx + j] = encoding[(v >>> ((7-j)*4)) & 0x0F];
}
}
return new String(encodedChars);
}
}
Testing this vs your original method using caliper (microbenchmark results here) shows this is around 11x faster † (caveat: on my machine). EDIT For anyone interested in running this and comparing the results, there is a gist here with the source code.
Even for a single element array
The original microbenchmark used Caliper as I happened to be trying it out at the time. I have rewritten it to use JMH. While doing so I found that the results I linked to and copied here originally used an array that was only ever filled with 0 for each int element. This caused the JVM to optimise the AltConverter code for arrays with length > 1 yielding artificial 10x to 11x improvements in AltConverter vs SimpleConverter. JMH and Caliper produce very similar results for both the flawed and corrected benchmark. (Updated benchmark project for maven eclipse here).
This is around 2x to 4x faster depending on array length (on my machine™). The mean runtime results (in ns) are:
Average run times in nanoseconds Original method: SimpleConverter New method: AltConverter | N | Alt / ns | error / ns | Simple / ns | Error / ns | Speed up | | ---------: | ---------: | ---------: | ----------: | ---------: | -------: | | 1 | 30 | 1 | 61 | 2 | 2.0x | | 100 | 852 | 19 | 3,724 | 99 | 4.4x | | 1000 | 7,517 | 200 | 36,484 | 879 | 4.9x | | 1000,0 | 82,641 | 1,416 | 360,670 | 5,728 | 4.4x | | 1000,00 | 1,014,612 | 241,089 | 4,006,940 | 91,870 | 3.9x | | 1000,000 | 9,929,510 | 174,006 | 41,077,214 | 1,181,322 | 4.1x | | 1000,000,0 | 182,698,229 | 16,571,654 | 432,730,259 | 13,310,797 | 2.4x |
† Disclaimer: Micro-benchmarking is dangerous to rely on as an indication of performance in a real world app, but caliper is a good benchmarking framework, jmh is imho better. A performance difference of 10x 4x, with very small standard deviation, in caliper a good t-test result is enough to indicate a good performance increase even inside a more complex application.
int val1 = a & 0xff;You throw away three bytes of every int.