Comparison of Java and C++: Difference between revisions

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** Prior to [[C++20]], C++ used a [[header file]] [[source code]] inclusion system to share declarations between source files. Since C++20, however, [[precompiled header#Modules|modules]] were introduced offering similar functionality to Java packages, however C++ modules do not have the same granularity of Java packages which allowing for importing individual classes - rather, in C++, all symbols marked <code>export</code> are accessible after importing a module, making it akin to a wildcard import in Java.

** 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.core</code>, <code>std.math</code>, and <code>std.io</code>.<ref name="P0581R1">C++ Standards Committee. (2018). ''P0581R1 - Modules for C++''. Retrieved from [https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0581r1.pdf https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p0581r1.pdf]</ref><ref name="P2412R0">C++ Standards Committee. (2021). ''P2412R0 - Further refinements to the C++ Modules Design''. Retrieved from [https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2021/p2412r0.pdf https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2021/p2412r0.pdf]</ref>

* 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 [[precompiled header#Modules|module]] represents a single [[translation unit]] that is declared as a module.

** <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 (more similar to <code>using</code> in C++). This is because all classes are handled as needed during runtime by the [[Java class loader]] on demand, and can be invoked even without "importing", simply by fully qualifying the class.

* 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.