import java.nio.charset.StandardCharsets;

import javax.xml.bind.DatatypeConverter;

class Ideone
{
    public static void main(String[] args)
    {
        final String string = "Hello, world!";
        final String hex = DatatypeConverter.printHexBinary(string.getBytes(StandardCharsets.UTF_8));
        System.out.println(new String(DatatypeConverter.parseHexBinary(hex), StandardCharsets.UTF_8));
    }
}