The invention of the design patterns that we commonly use today can be attributed to the following four persons: Erich Gamma, Richard Helm, Ralph Johnson and John Vlissides. These men invented 23 patterns in all that are commonly known as the Gang of Four patterns or the GOF patterns.  These patterns are named based on their intent and purpose and are classified in three broad categories stated below.

·         Creational

·         Structural

·         Behavioral

Each of these groups in turn contains related sub patterns.  These patterns are discussed in the sections that follow.  The sub patterns under the major three groups discussed above and their brief explanation are provided for better understanding.