README.md

Programming-tips

1. Sort string of arraylist

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Collections are used for sorting the string of arraylist

ArrayList list = new ArrayList();

Collections.sort(contactnamesList, new Comparator() { @Override public int compare(String o1, String o2) {
return o1.compareToIgnoreCase(o2); } });

2. Encrypt and Decrypt data

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mcrypt = new MCrypt();

/* Encrypt */ String encrypted = MCrypt.bytesToHex( mcrypt.encrypt("Text to Encrypt") );

/* Decrypt */ String decrypted = new String( mcrypt.decrypt( encrypted ) );

Below is the class file

import java.security.NoSuchAlgorithmException;

    import javax.crypto.Cipher;
    import javax.crypto.NoSuchPaddingException;
    import javax.crypto.spec.IvParameterSpec;
    import javax.crypto.spec.SecretKeySpec;

    public class MCrypt {

            private String iv = "fedcba9876543210";//Dummy iv (CHANGE IT!)
            private IvParameterSpec ivspec;
            private SecretKeySpec keyspec;
            private Cipher cipher;
            
            private String SecretKey = "0123456789abcdef";//Dummy secretKey (CHANGE IT!)
            
            public MCrypt()
            {
                    ivspec = new IvParameterSpec(iv.getBytes());

                    keyspec = new SecretKeySpec(SecretKey.getBytes(), "AES");
                    
                    try {
                            cipher = Cipher.getInstance("AES/CBC/NoPadding");
                    } catch (NoSuchAlgorithmException e) {
                            // TODO Auto-generated catch block
                            e.printStackTrace();
                    } catch (NoSuchPaddingException e) {
                            // TODO Auto-generated catch block
                            e.printStackTrace();
                    }
            }
            
            public byte[] encrypt(String text) throws Exception
            {
                    if(text == null || text.length() == 0)
                            throw new Exception("Empty string");
                    
                    byte[] encrypted = null;

                    try {
                            cipher.init(Cipher.ENCRYPT_MODE, keyspec, ivspec);

                            encrypted = cipher.doFinal(padString(text).getBytes());
                    } catch (Exception e)
                    {                       
                            throw new Exception("[encrypt] " + e.getMessage());
                    }
                    
                    return encrypted;
            }
            
            public byte[] decrypt(String code) throws Exception
            {
                    if(code == null || code.length() == 0)
                            throw new Exception("Empty string");
                    
                    byte[] decrypted = null;

                    try {
                            cipher.init(Cipher.DECRYPT_MODE, keyspec, ivspec);
                            
                            decrypted = cipher.doFinal(hexToBytes(code));
                    } catch (Exception e)
                    {
                            throw new Exception("[decrypt] " + e.getMessage());
                    }
                    return decrypted;
            }
            

            
            public static String bytesToHex(byte[] data)
            {
                    if (data==null)
                    {
                            return null;
                    }
                    
                    int len = data.length;
                    String str = "";
                    for (int i=0; i<len; i++) {
                            if ((data[i]&0xFF)<16)
                                    str = str + "0" + java.lang.Integer.toHexString(data[i]&0xFF);
                            else
                                    str = str + java.lang.Integer.toHexString(data[i]&0xFF);
                    }
                    return str;
            }
            
                    
            public static byte[] hexToBytes(String str) {
                    if (str==null) {
                            return null;
                    } else if (str.length() < 2) {
                            return null;
                    } else {
                            int len = str.length() / 2;
                            byte[] buffer = new byte[len];
                            for (int i=0; i<len; i++) {
                                    buffer[i] = (byte) Integer.parseInt(str.substring(i*2,i*2+2),16);
                            }
                            return buffer;
                    }
            }
            
            

            private static String padString(String source)
            {
              char paddingChar = ' ';
              int size = 16;
              int x = source.length() % size;
              int padLength = size - x;

              for (int i = 0; i < padLength; i++)
              {
                      source += paddingChar;
              }

              return source;
            }
    }

3. Remove duplicates from arraylist

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// this will remove duplicates from the given arraylist private static ArrayList RemoveDuplicate(ArrayList sourceList) { ArrayList list = new ArrayList(); foreach (string item in sourceList) { if (!list.Contains(item)) { list.Add(item); } } return list; }