GNU Compiler for Java

Template:Short description Template:Infobox software The GNU Compiler for Java (GCJ) is a discontinued free compiler for the Java programming language. It was part of the GNU Compiler Collection.<ref>Template:Cite web</ref><ref>Template:Cite book</ref>

GCJ compiles Java source code to Java virtual machine (JVM) bytecode or to machine code for a number of CPU architectures. It could also compile class files and whole JARs that contain bytecode into machine code.<ref>Template:Cite web</ref><ref>Template:Cite web</ref>

History

The GCJ runtime-libraries original source is from GNU Classpath project, but there is a code difference between the libgcj libraries. GCJ 4.3 uses the Eclipse Compiler for Java as a front-end.<ref> Template:Cite web </ref>

In 2007, a lot of work was done to implement support for Java's two graphical APIs in GNU Classpath: AWT and Swing. Software support for AWT is still in development. "Once AWT support is working then Swing support can be considered. There is at least one free-software partial implementations of Swing that may be usable.".<ref>The GCJ FAQ</ref> The GNU CLASSPATH was never completed to even Java 1.2 status and now appears to have been abandoned completely.

As of 2015, there were no new developments announced from GCJ and the product was in maintenance mode, with open-source Java toolchain development mostly happening within OpenJDK.<ref>GCC Looks To Turn Off Java, Replace With Go Or ADA</ref> GCJ was removed from the GCC trunk on September 30, 2016.<ref>Template:Cite web</ref><ref>Template:Cite web</ref> Announcement of its removal was made with the release of the GCC 7.1, which does not contain it.<ref>Template:Cite web</ref> GCJ remains part of GCC 6.

Performance

The compilation function in GCJ should have a faster start-up time than the equivalent bytecode launched in a JVM when compiling Java code into machine code.<ref>Template:Cite web</ref>

Compiled Native Interface (CNI)

The Compiled Native Interface (CNI), previously named "Cygnus Native Interface", is a software framework for the GCJ that allows Java code to call, and be called by, native applications (programs specific to a hardware and operating-system platform) and libraries written in C++.

CNI closely resembles the JNI (Java Native Interface) framework which comes as a standard with various Java virtual machines.

Comparison of language use

The authors of CNI claim for various advantages over JNI:<ref>The GCJ FAQ – GNU Project – Free Software Foundation (FSF)</ref>

CNI depends on Java classes appearing as C++ classes. For example,<ref>The example comes from: https://gcc.gnu.org/onlinedocs/gcj/Objects-and-Classes.html#Objects-and-Classes Template:Webarchive</ref> given a Java class,

<syntaxhighlight lang="java"> public class Int {

  public int i;
  public Int(int i) { this.i = i; }
  public static Int zero = new Int(0);

} </syntaxhighlight>

one can use the class thus:

<syntaxhighlight lang="cpp">

1. include <gcj/cni.h>
2. include <Int>

Int *mult(Int *p, int k) {

 if (k == 0)
   return Int::zero;  // Static member access.
 return new Int(p->i * k);

} </syntaxhighlight>

See also

• Excelsior JET (Excelsior Java native code compiler)
• IcedTea
• Kaffe
• SableVM
• JamVM
• Apache Harmony
• Jikes
• GraalVM - GraalVM's Native Image functionality is an ahead-of-time compilation technology that produces executable binaries of class files.
• Java virtual machine
• Free Java implementations
• Kotlin - Kotlin/Native is a technology for compiling Kotlin to native binaries that run without any JVM. It comprises a LLVM-based backend for the Kotlin compiler and a native implementation of the Kotlin runtime library.

External links

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