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Using the static keyword

From: Object-Oriented Programming with PHP

Video: Using the static keyword

Up to this point, the only way we've used classes is by instantiating, which can get a bit unwieldy. In this chapter, I'm going to introduce the concept of the static keyword, which gets around this limitation. I'll then demo how to access class contents without instantiation, set values that never change, and even how to create a method that doesn't require instantiation. Finally, we'll put it all together, and create a custom database class. But before we do that, let's start with the basics, avoiding instantiating. Sometimes, it's useful to access a property or method of a class without the overhead of actually instantiating an object.

Using the static keyword

Up to this point, the only way we've used classes is by instantiating, which can get a bit unwieldy. In this chapter, I'm going to introduce the concept of the static keyword, which gets around this limitation. I'll then demo how to access class contents without instantiation, set values that never change, and even how to create a method that doesn't require instantiation. Finally, we'll put it all together, and create a custom database class. But before we do that, let's start with the basics, avoiding instantiating. Sometimes, it's useful to access a property or method of a class without the overhead of actually instantiating an object.

Depending on the class, that instantiation might include connections to a database or third-party service, which can drag down performance when all you needed to do was get a default value. Also, before the release of PHP 5.3, the only way a developer could prevent a function or variable from having global scope was to declare it in a class. Finally, there are circumstances when you want to create only one instance of a class, and share it across the application, so it becomes important to be able to limit instance creation. To do this, we'll use the static keyword.

This makes the property or method accessible without needing instantiation. Static properties are unique in that their values are stored at a class level, not at an object's level. This can be useful to keep track of the number of instances, which I'll demonstrate in a bit. In the Address class, I want to keep track of the different types of addresses. For this demo, we'll keep it simple with three address types, each with a unique ID. Let's use 1 for residence, 2 for a business, and 3 for a park.

We're going to assign labels to these values, so we can display them to users, and even use the values for validation. As the address type is specific to addresses, we'll associate it with a class. By using the static keyword, we can expose these address types to other parts of the script without instantiation. To declare a property static, we'll use the same notation as we did with regular properties, including scope. The only difference is we'll add the keyword "static" somewhere before the property name. The order is actually flexible, but it's best practice to stay consistent. I prefer to start with static.

The declaration will end up looking something like static public $variable = . . . and so forth. Let's open the Address class. Then, I'm going to add the following to the top. Address types. static public $valid_ address_types = array, 1 is a residence, 2 is a business, and 3 is a park. Save, then open the demo file.

At the end, let's attempt to display these address types. echo

Displaying Address types . . . echo
 var_export, ($address->valid_address_types, TRUE),
						
							Then close pre and tt.  Save then reload the browser.
						
							Instead of the expected result, there  is an error message citing an undefined
						
							property. This is due to the static keyword.
						
					

In the next video, I will describe how to access a static property using a scope resolution operator.

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This video is part of

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Object-Oriented Programming with PHP

37 video lessons · 19218 viewers

Jon Peck
Author

 
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  1. 4m 10s
    1. Welcome
      39s
    2. Exercise files
      2m 16s
    3. What you should know
      1m 15s
  2. 7m 47s
    1. What is an object?
      2m 6s
    2. What is a class?
      2m 7s
    3. Why should you use object-oriented programming?
      2m 14s
    4. The history of object-oriented PHP
      1m 20s
  3. 16m 40s
    1. Defining a class
      2m 58s
    2. Defining class properties
      3m 26s
    3. Creating a method and exploring object context with $this
      2m 50s
    4. Instantiating an object and accessing its contents
      3m 19s
    5. Specifying the visibility scope
      4m 7s
  4. 15m 51s
    1. What is a magic method, and do I need one?
      2m 23s
    2. Overloading property access
      6m 37s
    3. Customizing object construction
      4m 34s
    4. Standardizing object rendering as a string
      2m 17s
  5. 20m 54s
    1. Using the static keyword
      3m 36s
    2. Leveraging scope resolution operators
      1m 10s
    3. Setting constant values
      2m 47s
    4. Implementing static methods
      5m 43s
    5. Creating a database class
      7m 38s
  6. 26m 19s
    1. Extending your class
      6m 8s
    2. Abstracting classes
      5m 57s
    3. Sharing interfaces using polymorphism
      4m 39s
    4. Overriding methods, properties, and constants
      3m 25s
    5. Cloning and comparing objects
      2m 51s
    6. Referencing objects
      3m 19s
  7. 14m 52s
    1. Leveraging standard class objects
      2m 42s
    2. Retrieving objects from the database
      5m 41s
    3. Error handling with exceptions
      2m 6s
    4. Customizing PHP exceptions
      4m 23s
  8. 8m 2s
    1. Identifying the singleton pattern
      1m 42s
    2. Using the factory method pattern
      1m 51s
    3. Implementing a strategy pattern
      4m 29s
  9. 2m 57s
    1. Looking forward to namespaces
      47s
    2. Next steps
      1m 6s
    3. Goodbye
      1m 4s

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