[英]What are the differences between PHP and Java?

What are the main differences between PHP and Java that someone proficient in PHP but learning Java should know about?


Edit: I mean differences in the syntax of the languages, i.e their data types, how they handle arrays & reference variables, and so forth :)


4 个解决方案



Not an exhaustive list, and I'm PHP developer who did a tour of Java a while back so Caveat Emptor.


Every variable in Java needs to be prepended with a data type. This includes primitive types such as boolean, int, double and char, as well as Object data-types, such as ArrayList, String, and your own objects


int  foo    = 36;
char bar    = 'b';
double baz  = 3.14;
String speech = "We hold these truths ...";
MyWidget widget = new MyWidget(foo,bar,baz,speech);

Every variable can only hold a value of its type. Using the above declarations, the following is not valid


foo = baz

Equality on objects (not on primitive types) checks for object identity. So the following un-intuitively prints false. Strings have an equality method to handle this.


//see comments for more information on what happens 
//if you use this syntax to declare your strings
//String v1 = "foo";
//String v2 = "foo";

String v1 = new String("foo");
String v2 = new String("foo");

if(v1 == v2){

Arrays are your classic C arrays. Can only hold variables of one particular type, need to be created with a fixed length


To get around this, there's a series of collection Objects, one of which is named ArrayList that will act more like PHP arrays (although the holds one type business is still true). You don't get the array like syntax, all manipulation is done through methods

为了解决这个问题,有一系列集合对象,其中一个名为ArrayList,它的行为更像PHP数组(尽管hold one type business仍然是true)。没有像语法一样的数组,所有操作都是通过方法完成的。

//creates an array list of strings
ArrayList<String> myArr = new ArrayList<String>();
myArr.add("My First Item"); 

ArrayLists still have numeric keys. There's another collection called HashMap that will give you a dictionary (or associative array, if you went to school in the 90s) like object.


ArrayLists and other collections are implemented with something called generics (the <String>). I am not a Java programmer, so all I understand about Generics is they describe the type of thing an Object will operate on. There is much more going on there.

arraylist和其他集合是用泛型实现的( )。我不是Java程序员,所以我对泛型的理解是它们描述了对象将要操作的对象的类型。还有更多的事情要做。

Java has no pointers. However, all Objects are actually references, similar to PHP 5, dissimilar to PHP 4. I don't think Java has the (depreciated) PHP &reference &syntax.

Java没有指针。但是,所有对象实际上都是引用,类似于PHP 5,与PHP 4不同。我不认为Java有(贬值的)PHP和引用和语法。

All method parameters are passed by value in Java. However, since all Objects are actually references, you're passing the value of the reference when you pass an object. This means if you manipulate an object passed into a method, the manipulations will stick. However, if you try something like this, you won't get the result you expect


public void swapThatWontWork(String v1, String v2)
  String temp = var1;
  var1 = var2;
  var2 = temp;

It's as good a time as any to mention that methods need to have their return type specified, and bad things will happen if an method returns something it's not supposed to. The following method returns an int


public int fooBarBax(int v1){

If a method is going to throw an exception, you have to declare it as such, or the compiler won't have anything to do with it.


public int fooBarBax(int v1) throws SomeException,AnotherException{

This can get tricky if you're using objects you haven't written in your method that might throw an exception.


You main code entry point in Java will be a method to a class, as opposed to PHPs main global entry point


Variable names in Java do not start with a sigil ($), although I think they can if you want them to


Class names in Java are case sensitive.


Strings are not mutable in Java, so concatenation can be an expensive operation.


The Java Class library provides a mechanism to implement threads. PHP has no such mechanism.


PHP methods (and functions) allow you have optional parameters. In java, you need to define a separate method for each possible list of parameters


public function inPHP($var1, $var2='foo'){}

public void function inJava($var1){
    $var2 = "foo";
public void function inJava($var1,$var2){


PHP requires an explicit $this be used when an object calls its own methods methods. Java (as seen in the above example) does not.


Java programs tend to be built from a "program runs, stays running, processes requests" kind of way, where as PHP applications are built from a "run, handle the request, stop running" kind of way.




I think these two languages (as well as their runtime systems) are too different to list all differences. Some really big ones that come to my head:


  • Java is compiled to bytecode, PHP is interpreted (as Alan Storm pointed out, since PHP 4, it’s not, but it still behaves as if it was);
  • Java被编译成字节码,PHP被解释(正如Alan Storm所指出的,因为PHP 4不是,但它仍然表现得好像它是);
  • Java is strong and statically typed, while PHP is rather weakly and dynamically typed;
  • Java是强类型和静态类型,而PHP是弱类型和动态类型;
  • PHP is mostly used to dynamically generate Web pages. Java can do that too, but can do anything else as well (like Applets, mobile phone software, Enterprise stuff, desktop applications with and without GUI, 3d games, Google Web Toolkit...); and
  • PHP主要用于动态生成Web页面。Java也可以做到这一点,但也可以做其他任何事情(比如applet、手机软件、企业产品、带GUI和不带GUI的桌面应用程序、3d游戏、谷歌Web Toolkit…);和
  • add your favourite difference here
  • 在这里加入你最喜欢的不同之处

You will notice most differences when it’s time to, but what’s most important:


  • PHP offers OOP (object-oriented programming) as an option that is ignored in most projects. Java requires you to program the OOP way, but when learning Java with a background in a not-so-OOP-language, it’s really easy to mess things up and use OOP the wrong way (or you might call it the sub-optimum way or the inefficient way...).
  • PHP提供了OOP(面向对象编程)作为大多数项目中都忽略的选项。Java要求您编写OOP方法,但是当您以不那么OOP语言的背景学习Java时,很容易把事情搞糟,用错误的方式使用OOP(或者您可能把它称为次优方法或低效方法…)。



  • Java is strongly-typed. PHP isn't;
  • Java是强类型的。PHP不;
  • PHP does a lot of implicit type conversion, which can actually be problematic and is why PHP5 has operators like === and !==. Java's implicit type conversion is primarily limited to auto-boxing of primitive types (PHP has no primitive types). This often comes up.
  • PHP进行了大量隐式类型转换,这实际上是有问题的,这也是为什么PHP5中有=== =和!=这样的操作符。Java的隐式类型转换主要局限于基本类型的自动装箱(PHP没有基本类型)。这经常出现。



$val = 'a';
if (strpos('abcdefghij', $val)) {
  // do stuff

which is incorrect and will have the block not executed because the return index of 0 is converted to false. The correct version is:


$val = 'a';
if (strpos('abcdefghij', $val) !== false) {
  // do stuff

Java conditional statements require an explicit boolean;


  • PHP variables and arrays are all prepended by $ and otherwise indistinguishable;
  • PHP变量和数组都以$开头,否则无法区分;
  • The equivalent of PHP associative arrays is PHP Maps (eg HashMap). Associative arrays are ordered on insertion order and can be used like ordinary arrays (on the values). Theres one Map implementation that maintains insertion order in Java but this is the exception rather than the norm;
  • PHP关联数组的等效值是PHP映射(如HashMap)。关联数组是按插入顺序排列的,可以像普通数组一样使用(在值上)。在Java中有一个维护插入顺序的映射实现,但这是一个例外,而不是规范;
  • $arr['foo'] = 'bar' insert or update an element in an associative array. Java must use Map.put() and Map.get();
  • $arr['foo'] = 'bar'插入或更新关联数组中的元素。Java必须使用Map.put()和Map.get();
  • PHP5 has the equivalent of function pointers and anonymous functions (using create_function()); 5.3 introduces closures at the language level. Java must use inner classes for both, which is somewhat more verbose. Moreover, inner classes are limited in how they can access variables from the outer scope (read Java Closures on JavaPapers), making them not as powerful as true closures.
  • PHP5具有等价的函数指针和匿名函数(使用create_function()));5.3在语言级别引入闭包。Java必须同时使用内部类,这有点冗长。此外,内部类在如何从外部范围(在javapap上读取Java闭包)访问变量方面受到限制,这使得它们不如真正的闭包强大。
  • Variable declaration is optional in PHP;
  • PHP中变量声明是可选的;
  • Use of global variables within functions requires explicit use of the global keyword in PHP;
  • 在函数中使用全局变量需要在PHP中显式地使用全局关键字;
  • POST/GET parameters are, unless configured otherwise (register_globals()) automatically result in global variables of the same name. They can alternatively be accessed via the $_POST global variable (and $_SESSION for session variables) whereas support for these things comes from a JEE add-on called the servlets API via objects like HttpServletRequest and HttpSession;
  • POST/GET参数是,除非配置其他参数(register_globals())),否则会自动生成同名的全局变量。它们也可以通过$_POST全局变量(以及会话变量$_SESSION)进行访问,而对这些内容的支持来自于一个名为servlets API的JEE扩展,其对象包括HttpServletRequest和HttpSession;
  • Function declaration in PHP uses the function keyword whereas in Java you declare return types and parameter types;
  • PHP中的函数声明使用Function关键字,而Java中声明返回类型和参数类型;
  • PHP function names can't normally clash whereas Java allows method overloading as long as the different method signatures aren't ambiguous;
  • PHP函数名通常不会冲突,而Java允许方法重载,只要不同的方法签名没有歧义;
  • PHP has default values for function arguments. Java doesn't. In Java this is implemented using method overloading.
  • PHP具有函数参数的默认值。Java没有。在Java中,这是通过方法重载实现的。
  • PHP supports the missing-method pattern, which is confusingly called "overloading" in the PHP docs.
  • PHP支持缺失方法模式,这在PHP文档中被混淆地称为“重载”。



function do_stuff($name = 'Foo') {
  // ...


void doStuff() {

void doStuff(String what) {
  // ...
  • String constants in PHP are declared using single or double quotes, much like Perl. Double quotes will evaluate variables embedded in the text. All Java String constants use double quotes and have no such variable evaluation;
  • PHP中的字符串常量使用单引号或双引号进行声明,这很像Perl。双引号将计算嵌入文本中的变量。所有Java字符串常量使用双引号,没有这样的变量评估;
  • PHP object method calls use the -> operator. Java uses the . operator;
  • PHP对象方法调用使用->操作符。Java使用。运营商;
  • Constructors in Java are named after the class name. In PHP they are called __construct();
  • Java中的构造函数以类名命名。在PHP中,它们被称为__construct();
  • In Java objects, this is implicit and only used to be explicit about scope and in certain cases with inner classes. In PHP5, $this is explicit;
  • 在Java对象中,这是隐式的,只用于显示范围,在某些情况下使用内部类。在PHP5中,这是显性的;
  • Static methods in Java can be called with either the . operator on an instance (although this is discouraged it is syntactically valid) but generally the class name is used instead.
  • Java中的静态方法可以用实例上的操作符(虽然不建议这样做,但语法上是有效的),但是通常使用类名。

These two are equivalent:


float f = 9.35f;
String s1 = String.valueOf(f);
String s2 = "My name is Earl".valueOf(f);

but the former is preferred. PHP uses the :: scope resolution operator for statics;


  • Method overriding and overloading is quite natural in Java but a bit of a kludge in PHP;
  • 方法重写和重载在Java中是很自然的,但在PHP中就有点复杂了;
  • PHP code is embedded in what is otherwise largely an HTML document, much like how JSPs work;
  • PHP代码嵌入到其他大部分HTML文档中,就像jsp是如何工作的;
  • PHP uses the . operator to append strings. Java uses +;
  • PHP使用。操作符添加字符串。Java使用+;
  • Java 5+ methods must use the ellipsis (...) to declare variable length argument lists explicitly. All PHP functions are variable length;
  • Java 5+方法必须使用省略号(…)显式地声明变量长度参数列表。所有PHP函数都是可变长度;
  • Variable length argument lists are treated as arrays inside method bodies. In PHP you have to use func_get_args(), func_get_arg() and/or func_num_args();
  • 变量长度参数列表被视为方法体中的数组。在PHP中,必须使用func_get_args()、func_get_arg()和/或func_num_args();
  • and no doubt more but thats all that springs to mind for now.
  • 毫无疑问还有更多,但这就是我现在想到的。



  • you could use JavaDoc tool to autogenerate documentation on your software. But you need to write comments in specific way.


  • you can't run PHP on mobile phones :) There are a lot of run time environments and platforms. That means you need to think in advance which libraries there could be missing or which limitations there could be (screen size, memory limits, file path delimiter "/" or "\" e.g).




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