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Error handling with exceptions

From: Object-Oriented Programming with PHP

Video: Error handling with exceptions

Exception handling is an object- oriented way of responding to abnormal or exceptional situations that can change program flow. Practically speaking, this means avoiding crashing. When there is serious fault, PHP creates what's known as an exception, which is a problem that needs to be dealt with. When an exception is created, it's thrown, which is kind of like telling everybody that there is a problem. To handle an exception, somebody must catch it, which means someone is listening, and dealt with the problem. To prepare for this, I need to surround the code that can throw an exception with a try block, followed by a catch.

Error handling with exceptions

Exception handling is an object- oriented way of responding to abnormal or exceptional situations that can change program flow. Practically speaking, this means avoiding crashing. When there is serious fault, PHP creates what's known as an exception, which is a problem that needs to be dealt with. When an exception is created, it's thrown, which is kind of like telling everybody that there is a problem. To handle an exception, somebody must catch it, which means someone is listening, and dealt with the problem. To prepare for this, I need to surround the code that can throw an exception with a try block, followed by a catch.

This is like me saying, "Let me try to do this action, and if it doesn't work, then I'll deal with the problem." If an exception is thrown and not caught, the program crashes. Not cool. Exceptions are good, as they are a much nicer and logical way of dealing with problems. Instead of just stopping or displaying an error, I've got a chance to gracefully recover, and do something else. I can intentionally throw an exception as well, which is good if a program requires something that is missing, or custom code is out of logical bounds.

To throw an exception, use the throw keyword followed by new, then the Exception class. Within the address example, there are several opportunities to throw an exception. An obvious place to start would be the attempt to load from the database. If a row is not found, then throw an exception. Open the Address class, and navigate to the load method. Following the if, there is a row check. Throw a new exception stating the problem. The first argument is the message.

throw new Exception ('Address_not_found'). Save, then edit the demo. Instead of loading address id 1, attempt to load address id 0, which does not exist. Save, then switch to the browser, and refresh. You will see an uncaught exception. In the next video, I will demonstrate how to catch this exception, then how to customize exceptions to meet your needs.

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Object-Oriented Programming with PHP

37 video lessons · 17430 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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