What is the difference between php const and static variables

Difference: Once defined, const cannot be changed, while variables modified by static can be changed. const can only modify class attributes, not class methods; static can modify attributes as well as methods.

The operating environment of this tutorial: windows7 system, PHP7.1 version, DELL G3 computer

static and The difference between const variables

static variables

1.static static variables we can modify them , but we cannot modify const variables
2.static static variables can modify permissions
3.Similar to java, inside the class, satic The body of the modified method cannot access non-staic member variables of the class, but can only access the class's staic variables and the class's const constants

class staticTest1 {
    var $var1 = "hello";
    public static $var2 = "hellostatic"; //public, protected, private
    const var3 = "helloconst";
    public static function displayDifferent(){
###        echo $this->$var1."<br>";//不能访问普通变量
        echo staticTest1::$var2."<br>";//可以访问类的静态变量
        echo self::var3."<br>";//不能用$this::var3, self::var3代表当前类，$this::var3代表当前对象
    }
}

//You can call the method in two ways

//第一种，通过对象调用
$test1 = new staticTest1();
echo $test1->displayDifferent();
echo "<br>";
//第二种，通过类调用
echo staticTest1::displayDifferent();
echo "<br>";

By the way, "::" can only access static variables and methods for objects, and self can only use "::" to call members of the current class

const variables

1. Const variables can only modify member variables, not methods
2. No modification permission is required
3 .Because const variables belong to the entire class and do not belong to an object, they cannot be accessed through objects. For example, $this->constvariable does not allow

class constTest1 {
    var $var1 = "welcome";
//    public const pi = 3.14;//不能加修饰权限
    const pi = 3.14;
//    const function displayDifferent() {//function前不能加const
//        
//    }
   function displayDifferent() {
        echo self::pi."<br>";
//        echo $this::pi."<br>"; 
    }
    static function displayDifferent2() {
        echo self::pi."<br>";
//        echo $this::pi."<br>"; //这句话不行。
    }
}

two method calls

//第一种，通过对象调用
$test2 = new constTest1();
echo $test2->displayDifferent();
//第二种，通过类调用
//echo constTest1::displayDifferent();//对象名用"::"只能访问静态变量和方法,所以这个不行

echo constTest1::displayDifferent2();

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