Sophie: php-manual-en-4.3.0-2mdk noarch

php-manual-en-4.3.0-2mdk.noarch.rpm

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>Chapter 14. Classes and Objects</TD
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>Caution</B
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>&#13;     The following is valid for PHP 4 only.
    </P
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>&#13;    Sometimes it is useful to refer to functions and variables
    in base classes or to refer to functions in classes that
    have not yet any instances. The :: operator is being used
    for this.
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>class A
{
    function example()
    {
        echo "I am the original function A::example().&#60;br&#62;\n";
    }
}

class B extends A
{
    function example()
    {
        echo "I am the redefined function B::example().&#60;br&#62;\n";
        A::example();
    }
}

// there is no object of class A.
// this will print
//   I am the original function A::example().&#60;br&#62;
A::example();

// create an object of class B.
$b = new B;

// this will print 
//   I am the redefined function B::example().&#60;br&#62;
//   I am the original function A::example().&#60;br&#62;
$b-&#62;example();</PRE
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>&#13;    The above example calls the function example() in
    class A, but there is no object of class A, so that
    we cannot write $a-&#62;example() or similar. Instead we
    call example() as a 'class function', that is, as a
    function of the class itself, not any object of that
    class.
   </P
><P
>&#13;    There are class functions, but there are no class variables.
    In fact, there is no object at all at the time of the call.
    Thus, a class function may not use any object variables (but
    it can use local and global variables), and it may no use
    $this at all.
   </P
><P
>&#13;    In the above example, class B redefines the function example(). 
    The original definition in class A is shadowed
    and no longer available, unless you are refering specifically
    to the implementation of example() in class A using the 
    ::-operator. Write A::example() to do this (in fact, you
    should be writing parent::example(), as shown in the next
    section).
   </P
><P
>&#13;    In this context, there is a current object and it may
    have object variables. Thus, when used from WITHIN an
    object function, you may use $this and object variables.
   </P
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