Comparison of Java and C++: Difference between revisions

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| 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 AccessInterface#Foreign Function and Memory API|Foreign Function and Memory API]] as a way to directly call C/C++ code. However, native languages are not safe and applications using native methods are susceptible to memory corruption.{{sfn|Bloch|2018|loc=Chapter §11 Item 66: Use native methods judiciously|p=285}} If the code is not carefully written, native methods can lower the performance of the system because the garbage collector is incapable of monitoring or maintaining native memory usage, and there is a cost context-switching between native and non-native code.{{sfn|Bloch|2018|loc=Chapter §11 Item 66: Use native methods judiciously|p=285}}

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| [[Write once, compile anywhere]] (WOCA).

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| <syntaxhighlight lang="cpp">

class Foo { // Declares class Foo

private:

int x = 0; // Private Member variable. It will

// be initialized to 0, if the

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* 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. andC enumerations (<code>enum</code>) support implicit conversion to integer types (but not from integer types), while C++ enumerations (<code>enum class</code>) do not. Java enumerations can be {{code|public static enum { enumName1, enumName2 }|java}} and are used like classes. Another way is to make another class that extends <code>java.lang.Enum<E></code>) and may therefore define constructors, fields, and methods as any other class. As of [[C++11]], C++ supports [[C++11#Strongly typed enumerations|strongly-typed enumerations]] which provide more type-safety and explicit specification of the storage type.

* 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.