關鍵字是具有一定意義的字。在PHP語言的常規使用中，這些單字不能用作常數、變數名、方法名、類別名稱等。這些關鍵字在使用時會被PHP自動理解。這些 PHP 關鍵字與變數名稱一起使用時，可能會與實際關鍵字混淆。因此，這些關鍵字不應該用作變數名。
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以下是列表：
代碼：
<?php
//example to demonstrate abstract keyword
abstract class Program {
abstract protected function MethodOne();
public function display() {
echo '<br>'.$this->MethodOne();
}
}
class ProgramOne extends Program {
protected function MethodOne() {
echo '<br>'.'In MethodOne';
}
}
$objOne = new ProgramOne;
$objOne->display();
?>,輸出：
代碼：
<?php
//example to demonstrate and keyword
$a = 10;
$b = 11;
if($a ==10 and $b == 11) {
echo 'Result : True';
}
else
{
echo 'Result : False';
}
?>輸出：
代碼：
<?php
//example to demonstrate array keyword
$directions = array("e" => "east", "w" => "west", "n" => "north", "s" => "south");
print_r($directions);
?>輸出：
代碼：
<?php
//example to demonstrate array keyword
$directions = array("e" => "east", "w" => "west", "n" => "north", "s" => "south");
foreach($directions as $key=>$value) {
echo '<br>'. $key. '=>'.$value;
}
?>輸出：
代碼：
<?php
//use of break keyword without optional argument
$arr = array("water", "sky", "try", "sand");
foreach($arr as $key=>$value) {
if($value == 'try') {
break ; // can use break 1 also
}
echo '<br>'.$value;
}
?>輸出：
代碼：
<?php
//example to demonstrate case keyword
$i = 1;
while($i<5) {
switch($i) {
case 1:
echo "<br>"."One";
break;
case 2:
echo "<br>"."Two";
break;
case 3:
echo "<br>"."Three";
break;
default:
echo "<br>"."Default";
}
$i++;
}
?>輸出：
代碼：
<?php
//example to demonstrate catch keyword
function Operation()
{
try {
$num1 = 10;
$num2 = 0;
if($num1 / $num2) {
throw new Exception('Divide By Zero');
}
} catch (Exception $e) {
die($e->getMessage());
}
}
Operation();
?>輸出：
代碼：
<?php
//example to demonstrate class keyword
class ClassOne{
var $str = 'Hello World';
public function displayMethod() {
echo $this->str;
}
}
$obj = new ClassOne;
$obj->displayMethod();
?>輸出：
const 關鍵字用於使用賦值運算子來定義名稱和值，如下所示
const AGE= 29;
常數名稱的開頭沒有像普通變數的 $ 符號。
代碼：
<?php
// example to demonstrate default keyword
$fruits = 'Cherries';
switch ($fruits) {
case 'Apple':
echo "Apple";
break;
case 'Banana':
echo "Banana";
break;
case 'Papaya':
echo "Papaya";
break;
default:
echo "Fruit is not Apple, Banana or Papaya ";
break;
}
?>輸出：
代碼：
<?php
// example to demonstrate do keyword
$x = 2;
do {
if($x > 2)
{
echo 'x is greater than 2';
}
else{
echo 'x is less than 2';
}
} while ($x < 2);
?>輸出：
代碼：
<?php
//example to demonstrate die keyword
$conn = mysqli_connect('localhost','root','','dbname');
if(!$conn) {
die("Unable to connect ");
}
?>輸出：
代碼：
<?php // example to demonstrate echo keyword echo 'Hello! '; $name = 'John Doe'; echo 'My name is '. $name; ?>
輸出：
代碼：
<?php
// example to demonstrate else keyword
$a = 10;
if ($a > 5) {
echo "a is greater than 10";
} else {
echo "a is not greater than 10";
}
?>輸出：
代碼：
<?php
// example to demonstrate elseif keyword
$a = 10;
if ($a > 10) {
echo "a is greater than 10";
} elseif ($a == 10) {
echo "a is equal to 10";
} else {
echo "a is smaller than 10";
}
?>輸出：
代碼：
<?php
// example to demonstrate empty keyword
$str = 'Hello World!';
if(empty($str)) {
echo 'Variable is empty';
} else {
echo $str;
}
?>輸出：
代碼：
<?php // example to demonstrate endfor keyword for($i=0;$i<5;$i++) : echo "<br/>".$i; endfor; ?>
輸出：
代碼：
<?php // example to demonstrate endif keyword if ($a > 10): echo "a is greater than 10"; elseif ($a >10) : echo "a is equal to 10"; else: echo "a is not equal to 10"; endif; ?>
輸出：
代碼：
<?php // example to demonstrate endforeach keyword $arr = array(1,2,3,4,5,6,7,8,9,10); foreach ($arr as $key=>$value): echo '<br>'.$value; endforeach; ?>
輸出：
代碼：
<?php // example to demonstrate endswitch keyword $fruits = 'Cherries'; switch ($fruits): case 'Apple': echo "Apple"; break; case 'Banana': echo "Banana"; break; case 'Papaya': echo "Papaya"; break; default: echo "Fruit is not Apple, Banana or Papaya "; break; endswitch; ?>
輸出：
代碼：
<?php // example to demonstrate endwhile keyword $i = 0; while($i<5): echo "<br>".$i; $i++; endwhile; ?>
輸出：
Code:
<?php
//example to demonstrate eval keyword
$string1 = 'World';
$string2 = 'John Doe';
$string = 'Hello $string1 . My name is $string2';
echo "<br>".$string;
eval("\$string = \"$string\";");
echo "<br>".$string;
?>Output:
This keyword when encountered in a script, terminates the execution of the script.
Code:
<?php
//example to demonstrate extends keyword
class ParentClass {
var $string = 'PHP';
public function display() {
echo $this->string;
}
}
class ExtendClass extends ParentClass {
public function display() {
echo 'Hello World!';
}
}
$obj1 = new ExtendClass;
$obj1->display();
?>Output:
Code:
<?php
//example to demonstrate final keyword
class ParentClass {
var $string = 'PHP';
final public function display() {
echo $this->string;
}
}
class ExtendClass extends ParentClass {
public function display() {
echo 'Hello World!';
}
}
$obj1 = new ExtendClass;
$obj1->display();
?>Output :
Code:
<?php
//example to demonstrate catch keyword
try {
$num1 = 10;
$num2 = 0;
if($num1 / $num2) {
throw new Exception('Divide By Zero');
}
} catch (Exception $e) {
echo '<br>'.$e->getMessage();
}
?>Output:
Code:
<?php
// example to demonstrate for keyword
for($i=0; $i<10; $i++) {
if($i == 5) {
break;
}
echo '<br>'.$i;
}
?>Output :
Code:
<?php
// example to demonstrate foreach keyword
$array = array(10,20,30,40,50);
foreach($array as $value) {
echo '<br>'.$value/10;
}
?>Output:
Code:
<?php
function calSum($a , $b) {
$c = $a + $b;
return $c;
}
$result = calSum(10 , 20);
echo '<br> The sum : '.$result;
?>Output:
Code:
<?php
//example to demonstrate global keyword
$a = 10;
$b = 20;
function fun() {
global $a;
global $b;
$result = $a + $b;
return $result;
}
$f = fun();
echo 'The result is '.$f;
?>Output:
Code:
<?php
// example to demonstrate if keyword
$sum = 10;
if($sum == 10) {
echo 'Sum is 10';
} else {
echo 'Sum is not 10';
}
?>Output:
Code:
<?php
//example to demonstrate interface keyword
interface One
{
public function first();
}
class MainClass implements One {
public function first() {
echo 'This is the First function';
}
}
$obj = new MainClass;
echo $obj->first();
?>Output :
Code:
file.php
<?php //example to demonstrate include keyword $a = 'The Earth'; $b = 'Round'; ?>
index.php
<?php include 'file.php'; echo $a . ' is '. $b. ' in Shape'; ?>
Code:
file.php
<?php //example to demonstrate include_once keyword $a = 'The Earth'; $b = 'Round'; ?>
index.php
<?php Include_once 'file.php'; echo $a . ' is '. $b. ' in Shape'; ?>
Output:
Code:
<?php
//example to demonstrate instanceOf keyword
class MainClass
{
public function MainCLassMethod(){
echo 'Hello World!';
}
}
class ExtendedClass extends MainClass
{
public function ExtendedClassMethod(){
echo 'Have a Nice Day!';
}
}
$obj1 = new ExtendedClass;
var_dump($obj1 instanceOf ExtendedClass);
?>Output:
Code:
<?php
//example to demonstrate interface keyword
interface One
{
public function one();
}
interface Two
{
public function two();
}
class MainClass implements One, Two {
public function one() {
echo '<br> This is the one function';
}
public function two() {
echo '<br> This is the two function';
}
}
$obj = new MainClass;
echo $obj->one();
echo $obj->two();
?>Output:
Code:
<?php //example to demonstrate isset keyword $stringOne = ''; var_dump(isset($stringOne)); $stringTwo = NULL; var_dump(isset($stringTwo)); ?>
Output :
Code:
<?php
//example to demonstrate list keyword
$names = array('Ram','Mohan','Raghav');
list($person1, $person2, $person3) = $names;
echo "$person1, $person2 and $person3 are friends";
?>Output:
Code:
<?php
//example to demonstrate new keyword
class Student
{
public function score($name, $subject, $marks) {
echo "$name scored $marks marks in $subject";
}
}
$obj = new Student;
$obj->score('Sunil','Maths',90);
?>Output:
Code:
<?php
//example to demonstrate or keyword
$a = 10;
$b = 11;
if($a ==10 or $b == 12) {
echo 'Result : True';
}
else
{
echo 'Result : False';
}
?>Output :
Code:
<?php //example to demonstrate print keyword $str = "PHP Programming"; print($str); $stringOne = "Shyam, "; $stringTwo = "How are you?"; print "<br>"."Hello $stringOne $stringTwo"; ?>
Output :
Code:
<?php
//example to demonstrate private keyword
class MainClass
{
private $str = 'Private';
function PrivateMethod()
{
echo 'In '. $this->str. ' Method';
}
}
$obj = new MainClass();
$obj->PrivateMethod(); //Shows Private Method
?>Output:
Code:
<?php
//example to demonstrate public keyword
class MainClass
{
public $str = 'Public';
function PublicMethod()
{
echo 'In '. $this->str. ' Method';
}
}
$obj = new MainClass();
$obj->PublicMethod(); //Shows Public Method
?>Output:
Code:
<?php
//example to demonstrate protected keyword
class MainClass
{
protected $str = 'Protected';
function ProtectedMethod()
{
echo 'In '. $this->str. ' Method';
}
}
$obj = new MainClass();
$obj->ProtectedMethod(); //Shows Protected Method
?>Output:
Code:
<?php
//example to demonstrate return keyword
function sum() {
$a = 10;
$b = 20;
$c = $a +$b;
return $c;
}
$result = sum();
echo 'Sum : ' . $result;
?>Output:
Code:
<?php
//example to demonstrate switch keyword
$i= 3;
switch($i) {
case 1:
echo "<br>"."One";
break;
case 2:
echo "<br>"."Two";
break;
case 3:
echo "<br>"."Three";
break;
default:
echo "<br>"."Default";
}
?>Output:
Code:
<?php
//example to demonstrate throw keyword
function division($x, $y) {
try {
if($y == 0) {
throw new Exception('Divide By Zero');
}
}
catch (Exception $e) {
echo '<br>'.$e->getMessage();
}
}
division(10,0);
?>Output:
Code:
<?php
//example to demonstrate try keyword
try{
$arr = array();
$arr_length = count($arr);
if($arr_length == 0) {
throw new Exception('Error : Empty Array!');
}
else {
echo 'Array found';
print_r($arr);
}
}
catch(Exception $e) {
echo '<br>'.$e->getMessage();
}
?>Output:
Code:
<?php //example to demonstrate unset keyword echo 'Hello World!'.'<br>'; $a = 10; echo $a; unset($a); // echo $a; //this line when uncommented shows error : Undefined variable, as the variable is unset ?>
Output:
Code:
<?php
//example to demonstrate var keyword
class MainClass
{
var $str = 'PHP Programming';
public function displayMsg() {
echo $this->str;
}
}
$obj = new MainClass;
$obj->displayMsg();
?>Output:
Code:
<?php
//example to demonstrate while keyword
$i = 0;
while ($i<10) {
echo '<br>'. $i;
$i++;
}
?>Output:
In this article, you will learn about keywords in PHP with examples. These examples explain the usage of each of the keyword in PHP.
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