What is Gang of Four (GOF)?
In 1994, four authors Erich Gamma , Richard Helm , Ralph Johnson and John Vlissides published a book titled Design Patterns - Elements of Reusable Object-Oriented Software which initiated the concept of Design Pattern in Software development. These authors are collectively known as Gang of Four (GOF) . According to these authors design patterns are primarily based on the following principles of object orientated design. Program to an interface not an implementation Favor object composition over inheritance