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Java Anonymous Class Example: Java Explained

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An anonymous class in Java is a type of local class that does not have a name. Anonymous classes are typically used when you want to make a small and simple modification to an existing class or interface, or create an instance of a class or interface in a condensed or shorter way. In this article, you’ll learn when to use an anonymous class in Java, the benefits of using an anonymous class, and how to create an anonymous class. We’ll also provide a code example to demonstrate how anonymous classes work along with common mistakes to avoid when using anonymous classes.

What is an Anonymous Class in Java?

An anonymous class in Java is a type of local class that does not have a name. This means there is no class declaration before the Java code. Instead, you will create an instance of the class (or interface) in just one line of code. An anonymous class can also be thought of as being similar to an inner class, with the main difference being that it does not have a name.

Anonymous classes provide a concise way for developers to make minor modifications to a larger class, or creating instances with very few lines of code. This makes the code cleaner and more concise since the code does not reqwuire the class declaration before the code can be written. Moreover, since an anonymous class does not have a name, it cannot be reused in other areas of the program.

Anonymous classes are also useful for creating objects that are only used once, such as when creating a listener for a button click. This allows developers to create the object and use it without having to create a separate class for it. Additionally, anonymous classes can be used to create objects that are only used in a specific context, such as when creating a thread for a specific task.

When to Use Anonymous Classes

Anonymous classes are best used when you need to make small changes to an existing class or interface, or when you need to create an instance quickly and simply. For example, if you need to add one extra line of code to a single method of a larger class, using an anonymous class makes sense since it saves time and makes the code cleaner.

Additionally, anonymous classes are particularly useful when writing event handlers for graphical user interface components such as ActionListener, WindowListener, and Listener. This is because graphical user interface structures use many small classes and interfaces which can otherwise be complex and tedious to write.

Anonymous classes are also useful when you need to create a class that implements an interface but you don’t need to use it anywhere else. This is because you can create the class and use it in the same line of code, which makes the code more concise and easier to read.

Benefits of Using Anonymous Classes

Using anonymous classes helps make code more concise and less verbose by eliminating the need for a separate class declaration. This makes it much easier for developers to quickly create an instance of a larger class with one line of code. The use of anonymous classes also encourages developers to use inheritance and composition rather than relying on monolithic classes.

Furthermore, anonymous classes are useful when implementing multiple interface methods such as in graphical user interface components as mentioned previously. This is because they give developers the flexibility to choose which methods require minimal or no modification, while also allowing them to quickly extend the functionality of bigger classes by overriding methods from the same class.

Anonymous classes also provide a way to create objects with a single line of code, which can be useful when creating objects with a limited lifespan. This can be especially helpful when dealing with objects that are used for a short period of time, such as in a loop or a function call. Additionally, anonymous classes can be used to create objects with a specific set of properties, which can be useful when dealing with objects that need to be initialized with certain values.

How to Create an Anonymous Class in Java

Creating an anonymous class involves two main steps. First, you create an instance of a class or interface in one line of code. And then, after your first step, you override methods from that same class or interface. To create a new instance of an anonymous class, use the new keyword followed by the class or interface name, parameters, and the code block that implements the methods.

For example, to create a new instance of an anonymous class that extends the Runnable, use the following line of code:

Runnable runnable = new Runnable(){     public void run(){          // Some code here      }  };

Example of an Anonymous Class in Java Code

Anonymous classes are often used when creating event handlers for graphical user interfaces. This is because implementing interfaces such as Actionlistener, WindowListener, and Listener can often be tedious and complex. Here is an example of how to create an event handler in an anonymous class:

MyButton button = new MyButton();  button.addActionListener(new ActionListener(){      public void actionPerformed(ActionEvent e){          // Some code here      }  });

Understanding Java Anonymous Class Syntax

The syntax for creating an anonymous class is relatively straightforward once you understand the basic structure. Here is an overview of what the syntax looks like:

ClassOrInterfaceName identifier = new ClassOrInterfaceName(){      // some code here  };

In this syntax:

  • ClassOrInterfaceName: This is the name of the class or interface you are creating an instance of.
  • identifier: This is the identifier you give your instance.
  • Code block: This is where you will implement methods.

Common Mistakes When Using Anonymous Classes

When creating an anonymous class, it’s easy to make some fundamental errors when it comes to syntax and implementation. Here are some common mistakes that developers make when using anonymous classes:

  • Mixing up syntax: This can be avoided by double checking your syntax before you submit your code.
  • Incorrect scope modifiers: Make sure to use the correct scope modifiers (public, private, protected, etc.) when implementing methods.
  • Using multiple anonymous classes in one line: Multiple uses of anonymous classes in one line is poor practice and should be avoided.

Wrapping Up: Benefits of Learning How to Use Anonymous Classes

Anonymous classes are useful when making small changes or modifications to existing classes, or when quickly creating instances with a few lines of code. Learning how to use anonymous classes eliminates the need for long, verbose lines of code and makes code more concise and easier to maintain. Additionally, using anonymous classes encourages developers to use inheritance and composition rather than relying on monolithic classes.

Anand Das

Anand Das

Anand is Co-founder and CTO of Bito. He leads technical strategy and engineering, and is our biggest user! Formerly, Anand was CTO of Eyeota, a data company acquired by Dun & Bradstreet. He is co-founder of PubMatic, where he led the building of an ad exchange system that handles over 1 Trillion bids per day.

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