It is called method overriding to a new definition created within a class, for one or more methods inherited from its superclass.
The following example shows how to do it. This example is based on this previous entry: Understanding OOP Inheritance with Python
To override the inherited constructor of the Person class, follow these steps:
Enter a new declaration of the constructor method within the Employee class.
Add the parameters name,lastname,birthdate,department,email. Within the definition of the constructor add the attributtes self.name, self.lastname,self.birthdate,self.department and self.email then assign the corresponding parameters.
Add the following print instruction to the end of the constructor.
Fig 1. Modified constructor
In the main program add two new lines with the following two phrases:
"John works in department"
and concatenate the department attribute of the object John, with a period and
"John's email is "
and concatenate the email attribute of the object John with a period.
Fig 2. Main program
Run the code. As you can see the Jonh instance of the Employee class now accepts three parameters, because the Person constructor has been overriding.
In addition, the talk method remains the same inherited from Person.
Fig 3. Running the example
Hashing is one-way mathematical function that is relatively easy to compute, but significantly harder to reverse.
- The input can be any length.
- The output has a fixed length.
- The hash function is one way and is not reversible.
- Two different input values will almost never result in the same hash values.
The 8-bit checksum is one of the first hashing algorithms, and it is the simple form of a hash function. An 8-bit checksum calculates the hash by converting the message into binary numbers and then organizing the string of binary numbers into 8-bit chucks. The algorithm adds up the 8-bit values. The final step is to convert the result using a process called 2’s complement.
Modern Hashing Algorithms
Two of the most popular modern hashing algorithms are MD5 and SHA.
Message Digest 5 (MD5) Algorithm
MD5 is one-way function that makes it easy to compute a hash from the given input data but makes it very difficult to compute input data given only a hash value. MD5 produces a 128-bit hash value.
Secure Hash Algorithm
SHA-2 algorithms are the secure hash algorithms that the U.S government requires by law for use in certain applications. This includes use in other cryptographic algorithms and protocols, for the protection or sensitive unclassified information.
SHA-2 replaced SHA-1 with four additional hash functions:
- SHA-224 (224 bits)
- SHA-256 (256 bits)
- SHA-384 (384 bits)
- SHA-512 (512 bits)
SHA-2 is a stronger algorithm, and it is replacing MD5. The SHA family is the next-generation algorithms.
The following program shows how to implement modern hashing algorithms with C#.
Fig 1. Running the program, compare different algorithms.
Fig 2. Running the program, comparing and contrasting different outputs.
When choosing a hashing algorithm, use SHA-256 or higher as they are currently the most secure. In production implement SHA-256 or higher.