PHP标记四种风格：

// XML风格
<?php echo '<p>Order processed</p>'; ?>
// 简短风格
<? echo '<p>Order processed</p>'; ?>
// script style
<script language='php'> echo '<p>Order processed</p>'; </script>
// ASP style, 默认此风格是禁用的
<% echo '<p>Order processed</p>'; %>

var_dump($variable)

<?php 
// int
$x = 9895;
var_dump($x);
// boolean
$y = false;
var_dump($y);
// null
$nul = null;
var_dump($nul);
// array
$z = array("Volvo", "BMW", "Toyota");
var_dump($z);

constant: 常量不需要使用$符号；

<?php 
    define("GREETING", "constant value");
// ture means NOT case sensitive
//    define("GREETING", "constant value", true);
    echo GREETING;

    // in class
class MyClass {
    const constant = '常量值';
    function showConstant() {
        // do not use $this, must "self"
        echo self::constant.PHP_EOL;
    }
}

class

<?php 
class Car {
    var $color;
    
    function Car($color = "green") {
        $this->color = $color;
    }

    function what_color() {
        return $this->color;
    }
}
//
class phpClass {
    var $var1;
    var $var2;
    var $var3 = "constant string";

    // 构造函数
    function __construct($par1, $par2) {  
        $this->var1 = $par1, 
        $this->var2 = $par2;
    }   
    // 析构函数
    function __destruct(void) {
        // destruct some member parameter
    }

    function myFunc($arg1, $arg2) {
        // some code here
    }
    // more functions
}

public, protected, private

class MyClass {
    var $var = 'var';              // default is public
    public $public = 'Public';
    protected $protected = 'Protected';
    private $private = 'Private';
    
    // default is public
    function myFunction() {
    }
    // public method
    public function publicFunction() {
    }
    // protected method
    protected function protectedFunction() {
    }
    // private method
    private function privateFunction() {
    }
}

interface：指定某个class必须实现哪些方法，接口中定义的方法必须都是公有的：

<?php
interface iTemplate {
    public function setVariable($name, $var);
    public function getHtml($template);
}

class Template implements iTemplate {
    public function setVariable($name, $var) {
    }

    public function getHtml($template) {
    }
}

abstract class: 至少一个方法声明为抽象， 这样的类不能实例化

<?php
abstract class AbstractClass {
    // just declaration
    abstract protected function prefixValue();
}

class ConcreteClass1 extends AbstractClass {
    protected function prefixValue() { // some code here }
}