Detailed explanation of php class constant definition and examples

What are class constants?

In php, we can understand that a quantity whose value does not change is called a constant. So, what is a class constant? In fact, class constants are also easy to understand. We can call the value that always remains unchanged in the class a constant, and this constant can be called a class constant. Be sure to remember that you do not need to use the "$" symbol when defining and using constants.

Class constants belong to the class itself, not to object instances, and cannot be accessed through object instances

* Cannot be modified with public, protected, private, static

* Subclasses can be repeated To write constants in the parent class, you can call the constants in the parent class through (parent::)

* Since PHP5.3.0, you can use a variable to dynamically call the class. But the value of this variable cannot be a keyword (such as self, parent or static).

Definition of class constants

Class constants are defined using the const keyword:

const 常量名 = 常量值

Example

Define and use a class constant

';
echo Foo::BAR, '
';
$obj = new Foo();
echo $obj->getConstant(), '
';
echo $obj->getConstantValue(), '
';
echo Foo::getConstantValue();
?>

Code running result:

Result In the above example, we use the subclass to rewrite the parent class constant, the code is as follows :

';
echo Foo::BAR, '
';
$obj = new Foo();
echo $obj->getConstant(), '
';
echo $obj->getConstantValue(), '
';
echo Foo::getConstantValue();
// 以上均输出PHP中文网
echo "
";
class Bar extends Foo
{
    const BAR = 'foo'; // 重写父类常量
    public static function getMyConstant()
    {
        return self::BAR;
    }
    public static function getParentConstant()
    {
        return parent::BAR;
    }
}
echo Bar::getMyConstant(),'
'; // foo
echo Bar::getParentConstant(); // PHP中文网
?>

Code running results:

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Detailed explanation of the definition and usage examples of PHP constants

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