Sumit MalviyaAre you looking to learn more about design patterns in Java? If so, you have come to the right place! In this blog post, we will explore the various types of design patterns in Java and how to use them effectively.
Since this is our second blog in the Advanced Java series, we will start with an overview of Design Patterns in Java. Then, we will dive into the types of each of these patterns, as well as how to use them effectively, with Java examples of these patterns.
| To better understand design patterns, it’s important to have a good understanding of object-oriented programming (OOP). Once you understand the basics of OOP, you’re ready to learn about design patterns. |
What are design patterns in Java?
Design patterns are a popular way to solve common problems in software development among software developers. They are defined as reusable solutions to common design problems, and they have been well-tested and documented in the software development community to solve problems in various software development languages. They were first introduced in the late 1970s by architect Christopher Alexander.
There are times when it can become difficult to organize and manage the code. This is where design patterns come in handy. For project success design patterns can be a powerful tool that can help you write code more efficiently and organize your code base in a more organized way.
Additionally, creating and using patterns in Java projects fosters software reuse, as they are already identified to provide standard conventions to solving those recurring problems.
Java design patterns are divided into three categories – creational, structural, and behavioral design patterns. Refer to the table below 👇 for a better understanding of all three categories and their types:
| Java Design Patterns |
| Creational Patterns | Structural patterns | Behavioral patterns |
| Factory Method | Adapter | Chain of Responsibility |
| Abstract Factory | Bridge | Command |
| Builder | Composite | Iterator |
| Prototype | Decorator | Mediator |
| Singleton | Facade | Memento |
| Flyweight | Observer | |
| Proxy | State | |
| Strategy | ||
| Template Method | ||
| Visitor |
Creational Patterns
Creational Patterns are design patterns that help you create objects and interfaces in code from scratch. If you’re a developer, you’re probably familiar with this. They provide various object creation mechanisms that you can use to write code that is more reusable and easier to understand. While creational patterns are particularly useful in Java due to its inheritance model, developers can apply them to any language.
There are various creational patterns to choose from. Because each pattern is used to solve a different problem when creating objects or building systems, and each has advantages and disadvantages when used. It’s important to understand them before using them in your projects.
The most popular Creational design patterns
| Design Pattern | Intent |
|---|---|
| Singleton Pattern | A single pattern lets you create an object that can only be created once per program run, while providing a global access point to this instance. This can be useful when you need to keep track of a single instance of an object across multiple calls or threads. |
| Prototype Pattern | The prototype pattern is generally used when we want to create new objects by simply copying the prototype of the class. It lets you copy existing objects without making your code dependent on their classes. |
| Builder Pattern | The Builder Pattern helps you build complex object graphs step by step, providing simple abstractions for constructing objects from other objects in your program using the same construction code. The advantage is that you can use Builder Patterns regardless of the structure of an application – even if you don’t have a specific structure in mind. |
| Abstract Factory | Known as factory of factories, it lets you create families of related objects without specifying their concrete classes. These patterns work around a super-factory to create other factories. In the Abstract Factory pattern, an interface is responsible for creating a factory of related objects without explicitly declaring the classes of the objects. |
| Factory Method | Factory Method in its true sense provides an interface for creating objects in a superclass, without having to specify their class or interface upfront. This is handy when there are different types of objects that need to be created dynamically (for example, instances of a custom class). Instead of writing dozens (or even hundreds) of lines of code for each factory method call, use a Creational Pattern like the Factory Method instead! |
What are Structural Patterns?
Structural patterns are a key part of any Java developer’s toolkit. As a valuable tool that can simplify the code structure of your Java applications by identifying relationships. They play an important role in solving complex problems, and understanding how they work.
Specifically, these patterns deal with designing systems using modularity and cohesion principles borrowed from architecture design disciplines like engineering or architecture planning. Developers can use Structural Patterns to create reusable solutions for common problems.
Types of structural design patterns
There are 7 types of structural design patterns. Each of these structures has its own benefits and should be used in different situations, depending on the needs of your application.
Let’s take a quick look at each one and understand their purposes and use within Java applications.
| Before learning Structural Patterns, make sure you understand a few key design patterns. It will make them even more useful and manageable for you. |
| Design | Intent |
| Adapter Pattern | Adapter Pattern is used when you need to implement an interface into another according to client expectations, but don’t want to write all the code yourself. By using the Adapter Pattern, you can provide an implementation for an interface specific to a certain class or type. Which will allow other classes or modules to easily use this implementation, without having to write any extra code themselves.
For example, you might use the adapter pattern when you have a class that represents data from one interface, but you want to display it as if it were from another interface. |
| Bridge Pattern | The bridge pattern is used to separate abstraction (interface) from implementation, allowing the two to change independently. For the Bridge pattern, we’ll consider two layers of abstraction; one is the geometric shape (like triangle and square) which is filled with different colors (our second abstraction layer):
is to decouple an abstraction from its implementation |
| Composite Pattern | The Composite Pattern enables clients to operate on a hierarchy of objects. When we need two or more objects to work together, but don’t want them to share any common properties or methods. The composite pattern delegated responsibility for specific tasks down into lower-level subcomponents known as composites to each component. This allows all components involved in a composite pattern to remain loosely coupled, while still allowing them to work effectively.
Examples of this pattern include ListViewItem, TreeItem, and GridViewItem. |
| Decorator Pattern | Decorator is perhaps the most common of the three patterns; it allows you to extend (or decorate) existing objects without modifying their source code or changing their behavior fundamentally. It adds functionality to an object dynamically.
For example, you could use Decorator to add new methods or properties onto an object without having to rewrite its entire source codebase! |
| Facade Pattern | The Facade Pattern is similar to the composite pattern, that provides a streamlined interface to a library, framework, or any other complex collection of classes. By defining low-level APIs for classes or modules, without exposing too much information about those APIs directly onto other classes.
Using facade pattern, we can create custom classes that act like other classes, but with some extra functionality attached (for example, hiding internal data from view). |
| Flyweight Pattern | The flyweight pattern is helpful for reducing resource consumption by sharing data. It is common to store shared data in external data structures and temporarily pass it to objects when they are used. |
| Proxy Pattern | The Proxy Pattern is used when one object needs access to another object, but doesn’t want those other objects directly accessible from within their own objects. With the Proxy pattern, an object creates a proxy object that acts as an intermediary between the original object and the outside world. The proxy can then access both the original object as well as any external resources that may be required by this particular application instance. |
Behavioral Patterns
Behavioral patterns are designed to solve common problems that involve interacting with objects. In these patterns, algorithms are used to assign responsibilities to objects.
It helps you create well-defined behaviors with no-code every time you need them. These can be useful when you want to keep track of certain state or behavior across multiple objects without having to write code every time.
Types of behavioral patterns
Combining different types of behavioral design patterns often leads to more robust and efficient systems than would be possible with any one pattern alone! Here are some of the most popular behavioral patterns in Java:
| Design Pattern | Intent |
| Chain of Responsibility | Chain of Responsibility pattern can be used when two or more objects need access to a shared resource. Upon receiving the request it ensures that only one object at a time has access and handles allocating and releasing resources as necessary. |
| Command | Command pattern used to change a request into a stand-alone object that has all of the request’s details. With this transformation, you can allow undoable operations, delay or queue the request’s execution, and pass requests as method arguments. |
| Iterator | This pattern helps us retrieve elements from an array or collection one by one. It does this by maintaining a reference to the current element, so that we can continue processing even if there are no more elements left in the collection or array. Makes the code much faster than if we were using a for loop or any other type of looping construct. |
| Mediator | Mediator pattern deals with behavior of objects. It promotes loose coupling by keeping objects from referring to each other explicitly, and it lets you vary their interaction independently by restrictricting direct communications between them and forces them to collaborate only via a mediator object. |
| Memento | As the name suggests, it helps us save and restore the previous state of an object without violating encapsulation, captures and externalizes an object’s internal state. |
| Observer | Defines a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically. Understanding observer design patterns can make your Java coding much easier and faster! |
| State | Allows an object to alter its behavior when its internal state changes. An object’s class will appear to change. |
| Strategy | Defines a family of algorithms, encapsulates each one, and makes them interchangeable. Strategy lets the algorithm vary independently from clients that use it. |
| Template Method | Defines the skeleton of an algorithm in a method, deferring some steps to subclasses. Template Method lets subclasses redefine certain steps of an algorithm without changing the algorithm’s structure. |
| Visitor | Represents an operation to be performed on the elements of an object structure. Visitor lets you define a new operation without changing the classes of the elements on which it operates. |
One thing to keep in mind when using behavioral design patterns is that they’re typically implemented in Java language syntax.
This isn’t because Java is better than any other language for this task; it’s just easier, because many Java frameworks include support for these patterns out-of-the-box. If you want to implement these patterns yourself, you’ll need familiarity with Java syntax, as well as some common library functions. They are useful in isolation but are often combined for robust results.
When to Use Design Patterns?
There is no one answer to this question, since it depends on the situation. However, some of the most common reasons for using design patterns include: making your code more maintainable, reducing the amount of boilerplate you need to write, and making your code more reusable.
More to follow
This was our guide to What is Design Pattern in Java? Throughout this, we have given an overview of each design pattern’s functions, subsets, capabilities, and benefits. Now that we know what each pattern does and why developers should use them, it’s time to learn how each applies specifically to Java development projects. New readers can check initial blogs in the series as well.
The next blog in the series will be posted soon. Until next time, happy learning!!
Mannat Gupta
Sidharth Shukla
Neel Vithlani
Add comment