Constants in PHP5 PHP Object Oriented_PHP Tutorial

//Declare a final class Math
class Math{
const PI = 3.14;
public function __toString(){
return "This is the Math class." ;
}
//Here is a method for calculating the area of ​​a circle. Const constants are used.
//Pay attention to the method used, which is similar to static variables.
public final function areaOfCircular($r ){
return $r * $r * self::PI ;
}
public final function max($a,$b){
return $a > $b ? $a : $b ;
}
public function setPI($a){
self::PI = 3.1415;
}
}
echo Math::PI ;
?> ;

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//Declare a final class Math
class Math{
const PI = 3.14;
public function __toString(){
return "This is the Math class.";
}
//A method for calculating the area of ​​a circle is written here. Use Const constant,
//Note the method used, similar to static variables.
public final function areaOfCircular($r){
return $r * $r * self::PI ;
}
public final function max($a,$b){
return $a > $b ? $a : $b ;
}
}
echo Math::PI ;
?>

The constants defined by const in PHP5 are different from the methods of defining variables, and there is no need to add the $ modifier. const PI = 3.14; This will do.
Constant names defined using const are generally capitalized. This is a convention and is the same in any language.
If the defined constant consists of multiple words, use _ to connect them. This is also the convention.
For example, naming like MAX_MUMBER. A good naming method is something that programmers must pay attention to.
Constants in a class are similar to static variables, except that their value cannot be changed. We use classname::constantname to call this constant.