Java中转换为二进制的几种实现

public class HexUtil {

    private static final String[] DIGITS_UPPER =
            {"0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "A", "B", "C", "D", "E", "F"};

    public static void main(String[] args) throws DecoderException {

        System.out.println(toHex1((byte) -128));
        System.out.println(toHex2((byte) -128));
        System.out.println(toHex3((byte) -128));
        System.out.println(toHex4((byte) -128));
    }

    public static String toHex1(byte value) {
        int high = (value & 0xF0) >>> 4;
        int low = value & 0x0F;
        return DIGITS_UPPER[high] + DIGITS_UPPER[low];
    }

    public static String toHex2(byte value) {
        int high = (value >>> 4) & 0x0F;
        int low = value & 0x0F;
        return DIGITS_UPPER[high] + DIGITS_UPPER[low];
    }

    public static String toHex3(byte value) {
        int tmp = value;
        if (value < 0) {
            tmp = value + 256;
        }
        int high = tmp / 16;
        int low = tmp % 16;
        return DIGITS_UPPER[high] + DIGITS_UPPER[low];
    }

    public static String toHex4(byte value) {
        return String.format("%x", value);
    }

}

参考

补码