Java整数，以十六进制和整数

Question

I have the problem, that the method does not work as expected. In most cases it works. However there is a case it does not work. I have a byte array containing some values. In hex eg: 0x04 0x42 (littleEndian). If I use the method convertTwoBytesToInt, I get a really small number. It should be > 16000 and not smaller than 2000.

I have two methods:

private static int convertTwoBytesToInt(byte[] a){
    String f1 = convertByteToHex(a[0]);
    String f2 = convertByteToHex(a[1]);
    return Integer.parseInt(f2+f1,RADIX16);
}

private static byte[] convertIntToTwoByte(int value){
    byte[] bytes = ByteBuffer.allocate(4).putInt(value).array();
    System.out.println("Check: "+Arrays.toString(bytes));
    byte[] result = new byte[2];
    //big to little endian:
    result[0] = bytes[3];
    result[1] = bytes[2];
    return result;
}

I call them as follows:

    byte[] h = convertIntToTwoByte(16000);
    System.out.println("AtS: "+Arrays.toString(h));
    System.out.println("tBtInt: "+convertTwoBytesToInt(h));

If I use the value 16000, there is no problem, but if I use 16900, the integer value of "convertTwoBytesToInt" is 1060.

Any Idea?

Answer 1

Based on the example you provided, my guess is that convertByteToHex(byte) is converting to a single-digit hex string when the byte value is less than 0x10. 16900 is 0x4204 and 1060 is 0x424.

You need to ensure that the conversion is zero-padded to two digits.

A much simpler approach is to use bit manipulation to construct the int value from the bytes:

private static int convertTwoBytesToInt(byte[] a) {
    return ((a[1] & 0xff) << 8) | (a[0] & 0xff);
}