The Decorator pattern is used to dynamically add or override behavior of an object, while the Flyweight pattern is used to share objects that are costly to create.

The Decorator design pattern is used to attach additional responsibilities to an object dynamically. This allows for greater flexibility and modularity in the design of a system, as well as the ability to add or remove responsibilities as needed.

This means that when designing software, the focus should be on defining the interfaces between different components, rather than the specific implementations of those components. This makes the code more flexible and easier to maintain, as it reduces the amount of coupling between components.

The Null Object pattern is a behavioral design pattern that provides a default object as a representative of "null" in the context of design patterns.

The Command design pattern decouples the invoker of an operation from the target object that performs the operation. This allows for greater flexibility and modularity in the design of a system.

Flyweight pattern is a design pattern that uses shared objects to support large numbers of similar objects efficiently. The pattern involves creating a shared object that can be used by multiple clients, reducing the amount of memory required to store the objects. This pattern can be useful in situations where you need to create large numbers of similar objects, but you want to minimize the memory footprint of the application.

An example of Adapter pattern would be a TV with an HDMI port that needs to be connected to a DVD player with a composite video port. The adapter would convert the composite video output into HDMI, allowing the TV and DVD player to work together. This example demonstrates the adapter pattern by showing how two objects with incompatible interfaces can work together through the use of an adapter.

The Singleton pattern ensures that a class has only one instance and provides a global point of access to that instance, while the Prototype pattern provides a mechanism for creating object instances that are exact copies of a prototype object

Some of the design patterns used in the JDK library include Decorator, Mediator, State, and Strategy. These patterns are used in various classes and APIs of the Java Standard Library to provide a clean and efficient implementation of common design problems.

A Singleton class in Java can be created by declaring a private constructor and a public static method that returns the only instance of the class. This ensures that there is only one instance of the class in the JVM and that it can be easily accessed by other objects in the system.