Web Systems Development (CSC-215) Lecture 4: Functions and Objects Monday 12th February 2018

Class Test 1 Monday 19th February Lab based – bring laptops or have desktop ready Lectures 1-6 Duration: 30 minutes

Setting up netbeans with wampserver for debugging

A note on type casting

Implicit & Explicit Casting PHP is loosely typed Variable and its type is declared simply by using it Automatically converts types when needed, via implicit casting

What if this behavior causes problems in some situations? We need a way to override. What if this behavior causes problems in some situations?

Explicit Casting Script produces a float value (attempts to produce the most accurate result) What if you need an integer value?

Explicit Casting

PHP Cast Types

Php functions & objects

Defining a Function

Example: Cleaning up a full name

Returning an array

Passing by reference

Including & requiring files

Include Statement

Include Once

Require and require once Program continues to execute even if the include failed (will then fail where it was needed)

Check if function exists Because PHP is evolving rapidly

Php objects

Creating Objects

Accessing Objects

Cloning Objects Assigning will create an additional reference

Not working

Use clone to create new instances

Constructors

Destructors

This

Static methods Called on class, not object

Implicit property definition - allowed by PHP but bad programming practice

Constants in class

Property & Method Scope Public Outside code accesses Extending classes should inherit Protected Outside code should not access Private Extending classes should not inherit

Usage

Inheritance Deriving subclasses from pre-existing classes Only modify the parts that are different Using extends operator

The parent operator A method in a subclass with the same name as one in its parent class will override the parent class method The parent operator can be used to access the parent method if this behavior is not desired

Parent constructors must be called explicitly when needed

Prevent overriding by subclass

Lecture content adapted from chapter 5 of Learning PHP, MySQL, JavaScript, CSS & HTML5, 3rd Edition, by Robin Nixon.