<?php$instance = new stdClass();// 也可以这样做：$className = &#39;stdClass&#39;;$instance = new $className(); // Foo()?>

<?phpclass Test{    static public function getNew()//单例模式可以使用此方法    {        return new static;    }}    class Child extends Test {}$obj1 = new Test();$obj2 = new $obj1;var_dump($obj1 !== $obj2);//bool(true)$obj3 = Test::getNew();var_dump($obj3 instanceof Test);//bool(true)$obj4 = Child::getNew();var_dump($obj4 instanceof Child);//bool(true)?>

<?php Class Object{   public $foo="bar";};$objectVar = new Object();$reference =& $objectVar;$assignment = $objectVar;$cloneObj = clone $objectVar;$objectVar->foo = "qux";var_dump( $objectVar );var_dump( $reference );var_dump( $assignment );var_dump( $cloneObj );echo '--------------------', PHP_EOL;$objectVar = null;var_dump($objectVar);var_dump($reference);var_dump($assignment);var_dump($cloneObj);/*Result:object(Object)#1 (1) {  ["foo"]=>  string(3) "qux"}object(Object)#1 (1) {  ["foo"]=>  string(3) "qux"}object(Object)#1 (1) {  ["foo"]=>  string(3) "qux"}object(Object)#2 (1) {  ["foo"]=>  string(3) "bar"}--------------------NULLNULLobject(Object)#1 (1) {  ["foo"]=>  string(3) "qux"}object(Object)#2 (1) {  ["foo"]=>  string(3) "bar"}*/

<?phpspl_autoload_register(function ($class_name) {    require_once $class_name . &#39;.php&#39;;});$obj  = new MyClass1();$obj2 = new MyClass2();?>

<?phpclass Test{    private $foo;    public function __construct($foo)    {        $this->foo = $foo;    }    private function bar()    {        echo 'Accessed the private method.';    }    public function baz(Test $other)    {        // We can change the private property:        $other->foo = 'hello';        var_dump($other->foo);        // We can also call the private method:        $other->bar();    }}$test = new Test('test');$test->baz(new Test('other'));//string(5) "hello"//Accessed the private method.?>

<?php abstract class base {     public function inherited() {         $this->overridden();     }     private function overridden() {         echo 'base';     } } class child extends base {     private function overridden() {         echo 'child';     } } $test = new child(); $test->inherited(); ?> Output will be "base". If you want the inherited methods to use overridden functionality in extended classes but public sounds too loose, use protected. That's what it is for:) A sample that works as intended: <?php abstract class base {     public function inherited() {         $this->overridden();     }     protected function overridden() {         echo 'base';     } } class child extends base {     protected function overridden() {         echo 'child';     } } $test = new child(); $test->inherited(); ?> Output will be "child".

<?php    class A {        public static $B = &#39;1&#39;; # Static class variable.        const B = &#39;2&#39;; # Class constant.            public static function B() { # Static class function.        return &#39;3&#39;;    }    }echo A::$B . A::B . A::B(); # Outputs: 123

<?phpclass MyClass{    protected function myFunc() {        echo "MyClass::myFunc()\n";    }}class OtherClass extends MyClass{    // 覆盖了父类的定义    public function myFunc()    {        // 但还是可以调用父类中被覆盖的方法        parent::myFunc();        echo "OtherClass::myFunc()\n";    }}$class = new OtherClass();$class->myFunc();?>

<?phpclass Base {    public function sayHello() {        echo &#39;Hello &#39;;    }}trait SayWorld {    public function sayHello() {        parent::sayHello();        echo &#39;World!&#39;;    }}class MyHelloWorld extends Base {    use SayWorld;}$o = new MyHelloWorld();$o->sayHello();//Hello World!?>

<?phptrait A {    public function smallTalk() {        echo &#39;a&#39;;    }    public function bigTalk() {        echo &#39;A&#39;;    }}trait B {    public function smallTalk() {        echo &#39;b&#39;;    }    public function bigTalk() {        echo &#39;B&#39;;    }}class Talker {    use A, B {        B::smallTalk insteadof A;        A::bigTalk insteadof B;    }}class Aliased_Talker {    use A, B {        B::smallTalk insteadof A;        A::bigTalk insteadof B;        B::bigTalk as talk;    }}?>

<?phptrait HelloWorld {    public function sayHello() {        echo &#39;Hello World!&#39;;    }}// 修改 sayHello 的访问控制class MyClass1 {    use HelloWorld { sayHello as protected; }}// 给方法一个改变了访问控制的别名// 原版 sayHello 的访问控制则没有发生变化class MyClass2 {    use HelloWorld { sayHello as private myPrivateHello; }}?>

<?phptrait Hello {    public function sayHello() {        echo &#39;Hello &#39;;    }}trait World {    public function sayWorld() {        echo &#39;World!&#39;;    }}trait HelloWorld {    use Hello, World;}class MyHelloWorld {    use HelloWorld;}$o = new MyHelloWorld();$o->sayHello();$o->sayWorld();?>

<?phptrait Hello {    public function sayHelloWorld() {        echo &#39;Hello&#39;.$this->getWorld();    }    abstract public function getWorld();}class MyHelloWorld {    private $world;    use Hello;    public function getWorld() {        return $this->world;    }    public function setWorld($val) {        $this->world = $val;    }}?>

<?phpclass TestClass {    public static $_bar;}class Foo1 extends TestClass { }class Foo2 extends TestClass { }Foo1::$_bar = &#39;Hello&#39;;Foo2::$_bar = &#39;World&#39;;echo Foo1::$_bar . &#39; &#39; . Foo2::$_bar; // Prints: World World?>Example using trait:<?phptrait TestTrait {    public static $_bar;}class Foo1 {    use TestTrait;}class Foo2 {    use TestTrait;}Foo1::$_bar = &#39;Hello&#39;;Foo2::$_bar = &#39;World&#39;;echo Foo1::$_bar . &#39; &#39; . Foo2::$_bar; // Prints: Hello World?>

<?phptrait PropertiesTrait {    public $same = true;    public $different = false;}class PropertiesExample {    use PropertiesTrait;    public $same = true; // PHP 7.0.0 后没问题，之前版本是 E_STRICT 提醒    public $different = true; // 致命错误}?>

<?phpforeach(new class(10) {    public $public = [];    protected $protected = [3, 4, 5];    private $private = [6, 7, 8];    function __construct($value = 1)    {        for ($i=0; $i < $value; $i++) {             $this->public[] = $i;        }    }    function __destruct()    {        foreach ($this as $key => list($a, $b, $c)) {            print "$key => [$a, $b, $c]\n";        }    }} as $key => list($a, $b, $c)) {    print "$key => [$a, $b, $c]\n";}echo "\n";//Result:/*public => [0, 1, 2]public => [0, 1, 2]protected => [3, 4, 5]private => [6, 7, 8] */

<?phpclass MyIterator implements Iterator{    private $var = array();    public function __construct($array)    {        if (is_array($array)) {            $this->var = $array;        }    }    public function rewind() {        echo "rewinding\n";        reset($this->var);    }    public function current() {        $var = current($this->var);        echo "current: $var\n";        return $var;    }    public function key() {        $var = key($this->var);        echo "key: $var\n";        return $var;    }    public function next() {        $var = next($this->var);        echo "next: $var\n";        return $var;    }    public function valid() {        $var = $this->current() !== false;        echo "valid: {$var}\n";        return $var;    }}$values = array(1,2,3);$it = new MyIterator($values);foreach ($it as $a => $b) {    print "$a: $b\n";}?>

<?phpclass MyCollection implements IteratorAggregate{    private $items = array();    private $count = 0;    // Required definition of interface IteratorAggregate    public function getIterator() {        return new MyIterator($this->items);    }    public function add($value) {        $this->items[$this->count++] = $value;    }}$coll = new MyCollection();$coll->add('value 1');$coll->add('value 2');$coll->add('value 3');foreach ($coll as $key => $val) {    echo "key/value: [$key -> $val]\n\n";}?>

<?phpfunction compareObjects(&$o1, &$o2){    echo &#39;o1 == o2 : &#39; , var_export($o1 == $o2) . "\r\n";    echo &#39;o1 === o2 : &#39; , var_export($o1 === $o2) . "\r\n";}class Flag{    public $flag;    function __construct($flag = true) { $this->flag = $flag; }}class OtherFlag{    public $flag;    function __construct($flag = true) { $this->flag = $flag; }}$o = new Flag;$p = new Flag;$q = $o;$r = new OtherFlag;$s = new Flag(false);echo "Two instances of the same class\r\n";compareObjects($o, $p);echo "\r\nTwo references to the same instance\r\n";compareObjects($o, $q);echo "\r\nInstances of two different classes\r\n";compareObjects($o, $r);echo "Two instances of the same class\r\n";compareObjects($o, $s);//Result:/*Two instances of the same classo1 == o2 : trueo1 === o2 : falseTwo references to the same instanceo1 == o2 : trueo1 === o2 : trueInstances of two different classeso1 == o2 : falseo1 === o2 : falseTwo instances of the same classo1 == o2 : falseo1 === o2 : false */?>

<?phpclass A {    public static function who() {        echo __CLASS__;    }    public static function test() {        self::who();        static::who(); // 后期静态绑定从这里开始    }}class B extends A {    public static function who() {        echo __CLASS__;    }}B::test();//AB?>

<?php class Model {     public static function find()     {         echo static::$name;     } } class Product extends Model {     protected static $name = &#39;Product&#39;; } Product::find(); ?> Output: 'Product'

Notes on reference:A reference is not a pointer. However, an object handle IS a pointer. Example:<?phpclass Foo {  private static $used;  private $id;  public function __construct() {    $id = $used++;  }  public function __clone() {    $id = $used++;  }}$a = new Foo; // $a is a pointer pointing to Foo object 0$b = $a; // $b is a pointer pointing to Foo object 0, however, $b is a copy of $a$c = &$a; // $c and $a are now references of a pointer pointing to Foo object 0$a = new Foo; // $a and $c are now references of a pointer pointing to Foo object 1, $b is still a pointer pointing to Foo object 0unset($a); // A reference with reference count 1 is automatically converted back to a value. Now $c is a pointer to Foo object 1$a = &$b; // $a and $b are now references of a pointer pointing to Foo object 0$a = NULL; // $a and $b now become a reference to NULL. Foo object 0 can be garbage collected nowunset($b); // $b no longer exists and $a is now NULL$a = clone $c; // $a is now a pointer to Foo object 2, $c remains a pointer to Foo object 1unset($c); // Foo object 1 can be garbage collected now.$c = $a; // $c and $a are pointers pointing to Foo object 2unset($a); // Foo object 2 is still pointed by $c$a = &$c; // Foo object 2 has 1 pointers pointing to it only, that pointer has 2 references: $a and $c;const ABC = TRUE;if(ABC) {  $a = NULL; // Foo object 2 can be garbage collected now because $a and $c are now a reference to the same NULL value} else {  unset($a); // Foo object 2 is still pointed to $c}

Regarding constants defined with define() inside namespaces...define() will define constants exactly as specified.  So, if you want to define a constant in a namespace, you will need to specify the namespace in your call to define(), even if you&#39;re calling define() from within a namespace.  The following examples will make it clear.The following code will define the constant "MESSAGE" in the global namespace (i.e. "\MESSAGE").<?phpnamespace test;define(&#39;MESSAGE&#39;, &#39;Hello world!&#39;);?>The following code will define two constants in the "test" namespace.<?phpnamespace test;define(&#39;test\HELLO&#39;, &#39;Hello world!&#39;);define(__NAMESPACE__ . &#39;\GOODBYE&#39;, &#39;Goodbye cruel world!&#39;);echo \test\HELLO, PHP_EOL;//Hello world!echo namespace\HELLO, PHP_EOL;//Hello world!echo constant(&#39;\\&#39;. __NAMESPACE__ . &#39;\HELLO&#39;) , PHP_EOL;//Hello world!echo constant(__NAMESPACE__ . &#39;\HELLO&#39;) , PHP_EOL;//Hello world!echo HELLO, PHP_EOL;//Hello world!echo __NAMESPACE__, PHP_EOL;//test?>

<?phpdeclare(encoding=&#39;UTF-8&#39;);namespace MyProject {const CONNECT_OK = 1;class Connection { /* ... */ }function connect() { /* ... */  }}namespace { // 全局代码session_start();$a = MyProject\connect();echo MyProject\Connection::start();}?>

<?phpnamespace Foo\Bar\subnamespace;const FOO = 1;function foo() {}class foo{    static function staticmethod() {}}?>

<?phpnamespace Foo\Bar;include &#39;file1.php&#39;;const FOO = 2;function foo() {}class foo{    static function staticmethod() {}}/* 非限定名称 */foo(); // 解析为 Foo\Bar\foo resolves to function Foo\Bar\foofoo::staticmethod(); // 解析为类 Foo\Bar\foo的静态方法staticmethod。resolves to class Foo\Bar\foo, method staticmethodecho FOO; // resolves to constant Foo\Bar\FOO/* 限定名称 */subnamespace\foo(); // 解析为函数 Foo\Bar\subnamespace\foosubnamespace\foo::staticmethod(); // 解析为类 Foo\Bar\subnamespace\foo,                                  // 以及类的方法 staticmethodecho subnamespace\FOO; // 解析为常量 Foo\Bar\subnamespace\FOO                                  /* 完全限定名称 */\Foo\Bar\foo(); // 解析为函数 Foo\Bar\foo\Foo\Bar\foo::staticmethod(); // 解析为类 Foo\Bar\foo, 以及类的方法 staticmethodecho \Foo\Bar\FOO; // 解析为常量 Foo\Bar\FOO?>

<?phpnamespace Foo;function strlen() {}const INI_ALL = 3;class Exception {}$a = \strlen(&#39;hi&#39;); // 调用全局函数strlen$b = \INI_ALL; // 访问全局常量 INI_ALL$c = new \Exception(&#39;error&#39;); // 实例化全局类 Exception?>

<?phpnamespace testt;class cls {}function func($value=&#39;&#39;) {}const VAL = __NAMESPACE__; ?>

<?phpnamespace test {    include &#39;php.php&#39;;    //new testt\cls;    //Fatal error: Uncaught Error: Class &#39;test\testt\cls&#39; not found in D:\php\test\test.php:4    //new cls;  //Fatal error: Uncaught Error: Class &#39;test\cls&#39; not found in D:\php\test\test.php:5    new \testt\cls;    echo \testt\VAL, PHP_EOL;    \testt\func();}namespace tests {    use testt\cls;    use testt\VAL;//未报错，也没效果    use testt\func;//未报错，也没效果    //new testt\cls;    //Fatal error: Uncaught Error: Class &#39;test\testt\cls&#39; not found in D:\php\test\test.php:4    new cls;    new \testt\cls;    echo \testt\VAL, PHP_EOL;    //echo VAL, PHP_EOL;    //Notice:  Use of undefined constant VAL - assumed &#39;VAL&#39; in D:\php\test\test.php on line 19    \testt\func();    //func();   //Fatal error:  Uncaught Error: Call to undefined function test\func() in D:\php\test\test.php:21}namespace {        //new cls;  //Fatal error: Uncaught Error: Class &#39;cls&#39; not found in D:\php\test\test.php:12    new \testt\cls;    new testt\cls;    echo testt\VAL, PHP_EOL;    testt\func();}namespace {    use testt\cls;    use testt\VAL;//未报错，也没效果    use testt\func;//未报错，也没效果    new cls;    new \testt\cls;    new testt\cls;    echo testt\VAL, PHP_EOL;    testt\func();    //func();   //Fatal error:  Uncaught Error: Call to undefined function func() in D:\php\test\test.php:41}//Result/*testttestttestttestt */

<?phpnamespace test;class cls {}function func($value=&#39;&#39;) {}const VAL = __NAMESPACE__;namespace\func();echo namespace\VAL;//testecho constant(__NAMESPACE__ . &#39;\VAL&#39;);//testnew namespace\cls;

<?phpnamespace foo;use My\Full\Classname as Another;//为命名空间设置别名// 下面的例子与 use My\Full\NSname as NSname 相同use My\Full\NSname;// 导入一个全局类use ArrayObject;// importing a function (PHP 5.6+)use function My\Full\functionName;// aliasing a function (PHP 5.6+)use function My\Full\functionName as func;// importing a constant (PHP 5.6+)use const My\Full\CONSTANT;$obj = new namespace\Another; // 实例化 foo\Another 对象$obj = new Another; // 实例化 My\Full\Classname　对象NSname\subns\func(); // 调用函数 My\Full\NSname\subns\func$a = new ArrayObject(array(1)); // 实例化 ArrayObject 对象// 如果不使用 "use \ArrayObject" ，则实例化一个 foo\ArrayObject 对象func(); // calls function My\Full\functionNameecho CONSTANT; // echoes the value of My\Full\CONSTANT?>

<?phpnamespace test;class Exception extends \Exception {    protected $message = &#39;My Exception&#39;;}try {    throw new Exception;//如果未定义Exception类，则会报致命错误。} catch (\Exception $e) {    echo $e->getMessage();} finally {    echo PHP_EOL, "finally do";}//Result/*My Exceptionfinally do */