Strategy Pattern

Allows one of a family of algorithms to be selected on-the-fly at run-time.

Problem:

public class Encryptor {

    private String algorithmName;
    private String plainText;

    public Encryptor(String algorithmName){
       this.algorithmName=algorithmName;
   }
    public void encrypt(String plainText){
        if (algorithmName.equals("Aes")){
            System.out.println("Encrypting data using AES algorithm");
            AESEncryption.encrypt(plainText); 
        }
       else if (algorithmName.equals("Blowfish")){
            System.out.println("Encrypting data using Blowfish algorithm");
            BlowFishEncryption.encrypt(plainText); 
        }
    }

}

Client Class:

public class UserService {

    public void encryptUserPassword(String password) {
        Encryptor encryptor = new Encryptor("Aes"); 
        encryptor.encrypt(password); //Encrypting with AES
    }

    public void encryptCreditCard(String creditCard) {
        Encryptor encryptor = new Encryptor("BlowFish"); 
        encryptor.encrypt(creditCard); //Encrypting with BlowFish 
    }

}

Strategy Pattern applied:

public interface EncryptionStrategy {
    void encryptData(String plainText);
}

AES Encryption:

public class AesEncryptionStrategy implements EncryptionStrategy {

    public void encryptData(String plaintext) {
       System.out.println("-------Encrypting data using AES algorithm-------");
       //Implementation of AES Encryption
   }

}

BlowFish Encryption:

public class BlowFishEncryptionStrategy implements EncryptionStrategy {

    public void encryptData(String plaintext) {
       System.out.println("-------Encrypting data using BlowFish algorithm-------");
       //Implementation of BlowFish Encryption
   }

}

Encryptor

public class Encryptor {

    private EncryptionStrategy strategy;

    private String plainText;

    public Encryptor(EncryptionStrategy strategy){
        this.strategy=strategy;
    }
    public void encrypt(String planText){
        strategy.encryptData(plainText);
    }

}

Client Class:

public class UserService {

    public void encryptUserPassword(String password) {
        Encryptor encryptor = new Encryptor(AesEncryptionStrategy); 
        encryptor.encrypt(password); //Encrypting with AES
    }

    public void encryptCreditCard(String creditCard) {
        Encryptor encryptor = new Encryptor(BlowFishEncryptionStrategy); 
        encryptor.encrypt(creditCard); //Encrypting with BlowFish 
    }

}