S.java

import java.io.ByteArrayInputStream;
import java.io.ByteArrayOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;

/**
 * @author vladimir.dolzhenko
 * @since 2016-12-02
 */
public class S implements Serializable {
    private final byte[] values;
    private transient final int hashCode;

    public S(byte[] values) {
        this.values = values;
        this.hashCode = calcHashCode(values);
    }

    private static int calcHashCode(final byte[] bytes) {
        int hc = 17;
        for (byte b : bytes) {
            hc = (hc << 4) + hc + higher(b);
        }
        return hc;
    }

    public byte[] getValues() {
        return values;
    }

    public int getHashCode() {
        return hashCode;
    }

    private static int higher(byte b) {
        return b & (b >= 'a' && b <= 'z' ? 0xDF : 0xFF);
    }

    Object readResolve() {
        return new S(this.values);
    }

    public static void main(String[] args) throws Exception {
        final S s = new S("XXX".getBytes());

        final ByteArrayOutputStream bos = new ByteArrayOutputStream();
        ObjectOutputStream os = new ObjectOutputStream(bos);

        os.writeObject(s);

        os.flush();
        os.close();

        final ByteArrayInputStream bis = new ByteArrayInputStream(bos.toByteArray());

        final ObjectInputStream ois = new ObjectInputStream(bis);

        S s2 = (S) ois.readObject();

        System.out.println(s.getHashCode());
        System.out.println(s2.getHashCode());

    }
}