Hướng dẫn dùng define instantiating trong PHP
class Basic class definitions begin with the keyword The class name can be any valid label, provided it is not a PHP reserved word. A valid class name starts with a
letter or underscore, followed by any number of letters, numbers, or underscores. As a regular expression, it would be expressed thus: A class may contain its own constants, variables (called "properties"), and functions (called "methods"). Example #1 Simple Class definition
The pseudo-variable $this is available when a method is called from within an object context. $this is the value of the calling object. Warning Calling a non-static method statically throws an Error. Prior to PHP 8.0.0, this would generate a deprecation notice, and $this would be undefined. Example #2 Some examples of the $this pseudo-variable
B Output of the above example in PHP 7: $this is defined (A) Deprecated: Non-static method A::foo() should not be called statically in %s on line 27 $this is not defined. Deprecated: Non-static method A::foo() should not be called statically in %s on line 20 $this is not defined. Deprecated: Non-static method B::bar() should not be called statically in %s on line 32 Deprecated: Non-static method A::foo() should not be called statically in %s on line 20 $this is not defined. Output of the above example in PHP 8: $this is defined (A) Fatal error: Uncaught Error: Non-static method A::foo() cannot be called statically in %s :27 Stack trace: #0 {main} thrown in %s on line 27 new To create an instance of a class, the If a string containing the name of a class is used with
Example #3 Creating an instance
As of PHP 8.0.0, using Example #4 Creating an instance using an arbitrary expression In the given example we show multiple examples of valid arbitrary expressions that produce a class name. This shows a call to a function, string concatenation, and the
getSomeClass(): string Output of the above example in PHP 8: object(ClassA)#1 (0) { } object(ClassB)#1 (0) { } object(ClassC)#1 (0) { } object(ClassD)#1 (0) { } In the class context, it is
possible to create a new object by When assigning an already created instance of a class to a new variable, the new variable will access the same instance as the object that was assigned. This behaviour is the same when passing instances to a function. A copy of an already created object can be made by cloning it. Example #5 Object Assignment
= new SimpleClass();$assigned = $instance; The above example will output: NULL NULL object(SimpleClass)#1 (1) { ["var"]=> string(30) "$assigned will have this value" } It's possible to create instances of an object in a couple of ways: Example #6 Creating new objects
Child extends Test The above example will output: bool(true) bool(true) bool(true) It is possible to access a member of a newly created object in a single expression: Example #7 Access member of newly created object
The above example will output something similar to:
Properties and methodsClass properties and methods live in separate "namespaces", so it is possible to have a property and a method with the same name. Referring to both a property and a method has the same notation, and whether a property will be accessed or a method will be called, solely depends on the context, i.e. whether the usage is a variable access or a function call. Example #8 Property access vs. method call
bar() { The above example will output: That means that calling an anonymous function which has been assigned to a property is not directly possible. Instead the property has to be assigned to a variable first, for instance. It is possible to call such a property directly by enclosing it in parentheses. Example #9 Calling an anonymous function stored in a property
__construct() { The above example will output: extends A class can inherit the constants, methods, and properties of another class by using the keyword The inherited constants, methods, and properties can be overridden by redeclaring them with the same name defined in the parent class. However, if the parent class has defined a method or constant as final, they may not be overridden. It is possible to access the overridden methods or static properties by referencing them with parent::.
Example #10 Simple Class Inheritance
The above example will output: Extending class a default value Signature compatibility rules When overriding a method, its signature must be compatible with the parent method. Otherwise, a fatal error is emitted, or, prior to PHP 8.0.0, an Example #11 Compatible child methods
Extend1 extends Base The above example will output: The following examples demonstrate that a child method which removes a parameter, or makes an optional parameter mandatory, is not compatible with the parent method. Example #12 Fatal error when a child method removes a parameter
Extend extends Base Output of the above example in PHP 8 is similar to: Fatal error: Declaration of Extend::foo() must be compatible with Base::foo(int $a = 5) in /in/evtlq on line 13 Example #13 Fatal error when a child method makes an optional parameter mandatory
Extend extends Base Output of the above example in PHP 8 is similar to: Fatal error: Declaration of Extend::foo(int $a) must be compatible with Base::foo(int $a = 5) in /in/qJXVC on line 13 Warning Renaming a method's parameter in a child class is not a signature incompatibility. However, this is discouraged as it will result in a runtime Error if named arguments are used. Example #14 Error when using named arguments and parameters were renamed in a child class
B extends A { The above example will output something similar to: Fatal error: Uncaught Error: Unknown named parameter $foo in /in/XaaeN:14 Stack trace: #0 {main} thrown in /in/XaaeN on line 14 ::class The Example #15 Class name resolution
ClassName::class; The above example will output:
As of PHP 8.0.0, the Example #17 Object name resolution
The above example will output: Nullsafe methods and properties As of PHP 8.0.0, properties and methods may also be accessed with the "nullsafe" operator instead: The effect is similar to wrapping each access in an is_null() check first, but more compact. Example #18 Nullsafe Operator
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STAT = 'S' ; // no dollar sign for constants (they are always static) Hayley Watson ¶ 4 years ago
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