Content deleted Content added
| (14 intermediate revisions by 6 users not shown) | |||
Line 7:
{{Use dmy dates|date=January 2021}}
{{ProgLangCompare}}
[[Java (programming language)|Java]] and [[C++]] are two prominent [[Object-oriented programming|object-oriented]] [[programming language]]s. By many language popularity metrics, the two languages have dominated object-oriented and high-performance software development for much of the 21st century, and are often directly compared and contrasted. Java's syntax [[Java (software platform)#History|was based on C/C++]].
== Design aims ==
Line 28 ⟶ 27:
|-
| Compatible with [[C (programming language)|C]] source code, except for a few [[corner case]]s.
| Provides the [[Java Native Interface]] as well as [[Java Native Access]] and more recently [[Java Native
|-
| [[Write once, compile anywhere]] (WOCA).
Line 61 ⟶ 60:
|-
| [[Resource management (computing)|Resource management]] can be done manually or by automatic lifetime-based resource management ([[Resource Acquisition Is Initialization|RAII]]).
| Resource management must generally be done manually, or automatically via finalizers, though this is generally discouraged. Has try-with-resources for automatic scope-based resource management (version 7 onwards). Resources, such as memory, can be managed using [[Java Native Interface]] or the Java Foreign Function and Memory API (since Java 22), but requires calling external C/C++ code.
It can also be done using the internal API <code>sun.misc.Unsafe</code> but that usage is highly discouraged and will be replaced by a public API in an upcoming Java version.
|-
| Supports classes, structs ([[passive data structure]] (PDS) types), and unions, and can allocate them on the [[Dynamic memory allocation|heap]] or the [[Stack-based memory allocation|stack]].
| Classes are allocated on the [[Dynamic memory allocation|heap]]. [[Java version history#Java SE 6|Java SE 6]] optimizes with [[escape analysis]] to allocate some objects on the [[Stack-based memory allocation|stack]].
|-
| Allows explicitly overriding types, and some implicit narrowing conversions (for compatibility with C).
| Rigid [[type safety]] except for widening conversions.
|-
| The [[C++ Standard Library]] was designed to have a limited scope and functions, but includes language support, diagnostics, general utilities, strings, locales, containers, algorithms, [[Iterator#C++|iterators]], numerics, input/output, random number generators, regular expression parsing, threading facilities, type traits (for static type introspection) and Standard C Library. Networking is a planned feature but not finalized yet. The [[Boost (C++ libraries)|Boost library]]
A rich amount of third-party libraries exist for GUI and other functions like: [[Adaptive Communication Environment]] (ACE), [[Crypto++]], various [[XMPP]] [[Instant Messaging]] (IM) libraries,<ref name="XMPP Software » Libraries">{{cite web|title=XMPP Software » Libraries|url=http://xmpp.org/xmpp-software/libraries/|publisher=xmpp.org|access-date=13 June 2013}}</ref> [[OpenLDAP]], [[Qt (software)|Qt]], [[gtkmm]].
| The standard library has grown with each release. By version 1.6, the library included support for locales, logging, containers and iterators, algorithms, GUI programming (but not using the system GUI), graphics, multi-threading, networking, platform security, introspection, dynamic class loading, blocking and non-blocking I/O. It provided interfaces or support classes for [[XML]], [[XSLT]], [[MIDI]], database connectivity, naming services (e.g. [[LDAP]]), cryptography, security services (e.g. [[Kerberos (protocol)|Kerberos]]), print services, and web services. SWT offered an abstraction for platform-specific GUIs, but was superseded by [[JavaFX]] in the latest releases; allowing for graphics acceleration and CSS-themable UIs. Although it doesn't support any kind of "native platform look" support.
|-
| [[Operator overloading]] for most operators. Preserving meaning (semantics) is highly recommended.
| Operators are not overridable. The language overrides + and += for the <code>String</code> class.
|-
| Single and [[multiple inheritance]] of classes, including virtual inheritance.
| Only supports single inheritance of classes,{{sfn|Bloch|2018|loc=Foreword|pp=xi-xii}}
|-
| Compile-time templates. Allows for [[Turing complete]] meta-programming.
| [[Generics in Java|Generics]] are used to achieve basic type-parametrization, but they do not translate from source code to byte code due to the use of [[type erasure]] by the compiler. Java type-casts all generics to their lowest bound (<code>Object</code> if no such bound exists, otherwise <code>? extends T</code> is casted to <code>T</code>).
|-
| Function pointers, function objects, lambdas (in [[C++11]]), and interfaces (using abstract classes).
| Functions references, function objects and lambdas were added in [[Java 8]]. Classes (and interfaces, which are classes) can be passed as references as well through <code>SomeClass.class</code> and <code>someObject.getClass()</code>.
|-
| No standard inline documentation mechanism. Third-party software (e.g. [[Doxygen]]) exists. Standard library vendors may provide documentation comments, though it is not guaranteed.
| Extensive [[Javadoc]] documentation standard on all system classes and methods.
|-
Line 114 ⟶ 113:
| <syntaxhighlight lang="cpp">
class Foo { // Declares class Foo
private:
int x = 0; // Private Member variable. It will
// be initialized to 0, if the
Line 306:
* Java has both language and standard library support for [[Thread (computer science)|multi-threading]]. The <code>synchronized</code> [[Java keywords|keyword in Java]] provides [[mutual exclusion|mutex locks]] to support multi-threaded applications.{{sfn|Goetz|Peierls|Bloch|Bowbeer|2006|loc=§2.3.1 Intrinsic locks|pp=25-26}}{{sfn|Bloch|2018|loc=Chapter §11 Item 78: Synchronize access to shared mutable data|pp=126-129}} Java also provides libraries for more advanced multi-threading synchronizing. [[C++11]] has a defined memory model for multi-threading in C++, and library support for creating threads and for many synchronizing primitives. There are also many third-party libraries for this.
* C++ member functions can be declared as [[virtual function]]s, which means the method to be called is determined by the run-time type of the object (a.k.a. dynamic dispatching). By default, methods in C++ are not virtual (i.e., ''opt-in virtual''). In Java, methods are virtual by default, but can be made non-virtual by using the <code>[[final (Java)|final]]</code> keyword (i.e., ''opt-out virtual'').
* C and C++ enumerations are primitive types.
* Unary operators {{code|++}} and {{code|--}}: in C++ "The operand shall be a modifiable [[Value (computer science)|lvalue]]. [skipped] The result is the updated operand; it is an lvalue...",<ref>Standard for Programming Language C++ '11, 5.3.2 Increment and decrement [expr.pre.incr].</ref> but in Java "the binary numeric promotion mentioned above may include unboxing conversion and value set conversion. If necessary, value set conversion {and/or [...] boxing conversion} is applied to the sum prior to its being stored in the variable.",<ref>The Java™ Language Specification, Java SE 7 Edition, Chapters 15.14.2, 15.14.3, 15.15.1, 15.15.2, http://docs.oracle.com/javase/specs/</ref> i.e. in Java, after the initialization {{code|1=Integer i=2; ++i;|2=java}} changes the reference {{code|i}} by assigning new object, while in C++ the object is still the same.
Line 390:
* Java and C++ use different means to divide code into multiple source files.
** Java uses a [[Java package|package system]] that dictates the file name and path for all program definitions. Its compiler imports the executable [[class (file format)|class files]].
** Prior to [[C++20]], C++ used a [[header file]] [[source code]] inclusion system to share declarations between source files. Since C++20, however, [[
** Since [[C++23]], the C++ standard library can now be imported as a module, but must be imported in its entirety rather than importing specific packages of the library like in Java, with <syntaxhighlight lang="C++" inline>import std;</syntaxhighlight>. This may change in the future, with proposals to separate the standard library into more modules such as <code>std.
* The term "[[modular programming|module]]" refers to different things. In Java, a [[Java package#Modules|module]] is used to group several packages together, meanwhile in C++ a [[
** <code>import</code> in C++ imports a module by linking it at compilation, however in C++, modules do not dictate the namespace which a symbol belongs to. Meanwhile, <code>import</code> in Java does not actually "import" any code into a file, and is used to alias classes to avoid fully qualifying them
* A Java source file must match the namespace which of the public class it declares (it may be named anything if there are no public classes), and the package it belongs to must match the path it is located in. A package may only declare at most one public class (but may have multiple non-public classes).
* A C++ source file (whether a header or module) may have any arbitrary name, and may contain as many classes as the programmer desires. Modules have no requirement to match the path of its ___location.
| |||