Comparison of Java and C++: Difference between revisions

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** 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, [[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.fundamentalcore</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]].

** <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. 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.