1.1.1 Mathematics

1.1.2 Statistics

1.2.1 Uses of Structural Patterns

• Adapter design pattern
  Adapter patterns create a connection between interfaces of different classes; let’s take the real-life example; we have two applications created with two different programming languages. Now, you want to compile both applications on a single platform. The adapter works here as it changes the interface of one instance so that other instances can easily understand it. The adapter hides all the complex conversions.
• Bridge design pattern
  The bridge design pattern splits the abstraction from its implementation. Let’s take the example of the main socket, which controls the lights, fan, TV, and AC of the house. This main socket acts as a bridge between the house’s sub-switches that control turning ON/OFF of the utilities.
• Composite design pattern
  Composite design patterns are used where a group of identical instances is considered as one instance. This pattern creates a hierarchal structure of similar objects. For example, the composite pattern creates a class that includes the faction of its objects.
  Let’s understand the pattern with an example of grouping the teachers into different departments, classes will contain all the details of a teacher like a name, salary, address, and department, and composite teacher class will use teacher class to add teachers in a different department and print the teachers.
• Decorator design pattern
  Decorator design patterns are used whenever new functions are needed to be added to existing objects without changing the entire structure of the class. Decorator design pattern creates a new class that abstracts the original class and provides the newly added functionalities. Let’s discuss an example of a decorator design pattern for a clearer understanding. Suppose we need to develop an online ordering system of a well-known burger restaurant that takes all requirements from a customer like what kind of bun, patty, and cheese they need in the burger and according to the requirement estimate the burger price.
  Since customer customization may vary from customer to customer, creating classes for each type of customization will be a difficult task. Here we can create a decorator pattern class, which will contain all the information to customize the burger, like adding extra cheese, extra patty etc. The main class will be the burger with the regular base price. By using a decorator class, the burger class can be extended and the price can be added according to the customization.
• Façade design pattern
  Façade design patterns act like abstraction, which conceals all the inner complex details of the application and provides a simple interface to the client to access the applications. Let us consider an example of a grocery shop, which is equipped with loads of items. When a customer visits the shop for the first time, he is unable to search and find the items he wishes to purchase. So he gives a list to the shopkeeper and the shopkeeper gives the customer all the required items. This is an example of Facade design pattern.
• Flyweight design pattern
  Flyweight design patterns, as the name implies, are patterns that fly away from the weight, i.e., a memory from the application. It reduces the objects from the source code to release the memory and boosts the performance. Flyweight design can be called code optimization. Flyweight searches the objects that are similar and use them. In case no match is found, it creates a new object. Improving system performance is a non-functional and essential requirement of software as it affects its appearance. Suppose we have an application running too slow due to lines and lines of code written and wastage of cache; now, flyweight design patterns work here. It will eliminate all the similar objects that are created and waste memory.
• Private class
  This type of pattern is used for security purposes where data are crucial. Create a private class and store the data, which will be in the same state throughout the code. All variables defined in the private class are only accessible within its class. To access the private class attributes, you need to create their getters and setters. The private class is used where information needs to be hidden from the outside world and only displayed to you.
• Proxy
  Proxy is all about providing access. In proxy design patterns, a class is created, which represents the functionality of other classes. Let’s take the example of a credit card that acts as a proxy and contains all your bank account amounts.