myeclipse6 .0 .1 注册码 的生成算法

package test;  
import java.io.*;  
public class MyEclipseGen {  
    private static final String LL = "Decompiling this copyrighted software is a violation of both your license agreement and the Digital Millenium Copyright Act of 1998 (http://www.loc.gov/copyright/legislation/dmca.pdf). Under section 1204 of the DMCA, penalties range up to a $500,000 fine or up to five years imprisonment for a first offense. Think about it; pay for a license, avoid prosecution, and feel better about yourself.";  
    public String getSerial(String userId, String licenseNum) {  
        java.util.Calendar cal = java.util.Calendar.getInstance();  
        cal.add(1, 3);  
        cal.add(6, -1);  
        java.text.NumberFormat nf = new java.text.DecimalFormat("000");  
        licenseNum = nf.format(Integer.valueOf(licenseNum));  
        String verTime = new StringBuilder("-").append(new java.text.  
                SimpleDateFormat("yyMMdd").format(cal.getTime())).append("0").  
                         toString();  
        String type = "YE3MP-";  
        String need = new StringBuilder(userId.substring(0, 1)).append(type).  
                      append("300").append(licenseNum).append(verTime).toString();  
        String dx = new StringBuilder(need).append(LL).append(userId).toString();  
        int suf = this.decode(dx);  
        String code = new StringBuilder(need).append(String.valueOf(suf)).  
                      toString();  
        return this.change(code);  
    }  
    private int decode(String s) {  
        int i;  
        char[] ac;  
        int j;  
        int k;  
        i = 0;  
        ac = s.toCharArray();  
        j = 0;  
        k = ac.length;  
        while (j < k) {  
            i = (31 * i) + ac[j];  
            j++;  
        }  
        return Math.abs(i);  
    }  
    private String change(String s) {  
        byte[] abyte0;  
        char[] ac;  
        int i;  
        int k;  
        int j;  
        abyte0 = s.getBytes();  
        ac = new char[s.length()];  
        i = 0;  
        k = abyte0.length;  
        while (i < k) {  
            j = abyte0[i];  
            if ((j >= 48) && (j <= 57)) {  
                j = (((j - 48) + 5) % 10) + 48;  
            } else if ((j >= 65) && (j <= 90)) {  
                j = (((j - 65) + 13) % 26) + 65;  
            } else if ((j >= 97) && (j <= 122)) {  
                j = (((j - 97) + 13) % 26) + 97;  
            }  
            ac[i] = (char) j;  
            i++;  
        }  
        return String.valueOf(ac);  
    }  
    public MyEclipseGen() {  
        super();  
    }  
    public static void main(String[] args) {  
        try {  
            System.out.println("please input register name:");  
            BufferedReader reader = new BufferedReader(new InputStreamReader(  
                    System.in));  
            String userId = null;  
            userId = reader.readLine();  
            MyEclipseGen myeclipsegen = new MyEclipseGen();  
            String res = myeclipsegen.getSerial(userId, "20");  
            System.out.println("Serial:" + res);  
            reader.readLine();  
        } catch (IOException ex) {  
        }  
    }  
}