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Java Operator Overloading

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Java Operator Overloading

Java-OO is a modular extension (plugin) to Java compilers and IDEs for (Scala-like) Operator Overloading support. Works with standard JavaC compiler, Netbeans IDE, Eclipse IDE, IntelliJ IDEA IDE and any build tools.

Example (see other examples at examples/ dir):

import java.math.*;
import java.util.*;
public class Test {
  public static void main(String[] args) {
    BigInteger a = BigInteger.valueOf(1), // without OO
               b = 2, // with OO

c1 = a.negate().add(b.multiply(b)).add(b.divide(a)), // without OO
c2 = -a + b*b + b/a; // with OO

if (c1.compareTo(c2)<0 || c1.compareTo(c2)>0) // without OO
if (c1<c2 c1>c2) // with OO

HashMap<string string> map = new HashMap&lt;&gt;();
if (!map.containsKey("qwe")) map.put("qwe", map.get("asd")); // without OO
if (map["qwe"]==null) map["qwe"] = map["asd"]; // with OO

} }


JavaC/Netbeans: 0.5
JavaC8:         0.5
Eclipse:        0.5
IntelliJ IDEA:  0.7

Note plugin versions are independent. If version for X > version for Y then it doesn't mean Y is behind feature wise.


16 Nov 2019. IntelliJ IDEA plugin v0.7 released with support of IDEA 2019.2+.

20 May 2017. IntelliJ IDEA plugin v0.6 released with support of IDEA 2017.

14 July 2016. As a workaround Eclipse plugin works fine on Eclipse 4.4+ if you install Scala IDE plugin first.

2 Feb 2016. IntelliJ IDEA plugin v0.5 released with support of IDEA 15. Requires Java8 to run the plugin.

10 April 2015. IntelliJ IDEA plugin v0.4.1 released with support of IDEA 14.1.

27 January 2015. Eclipse-oo-plugin version 0.5 released with support of reverse binary operator overload.

2 December 2014. New feature: Reverse binary operator overload via

Plugin versions updated:
JavaC7 & JavaC8: 0.5
IntelliJ IDEA: 0.4. Support of IDEA 14

31 May 2014. Javac8 plugin version 0.1.1 released. Removed runtime depencendy on nbjavac.

24 May 2014. IntelliJ IDEA plugin v0.3.1 released. Bugfixes for IDEA 13 Ultimate and for type resolution for binary expressions with primitives.

30 April 2014. IJPLA published a paper about Java-OO.

3 Feb 2014. New JavaC8 plugin version 0.1 for JDK8 was released. It has the same features as JavaC plugin for JDK7 but doesn't work in Netbeans yet.

12 Jan 2014. JavaC plugin version 0.4 and Eclipse plugin version 0.4 released. Now operator overloading perform autoboxing/autounboxing primitive to/from wrapper types where appropriate. Fixed javac plugin bug with index-set OO.

3 Jan 2014. JavaC plugin version 0.3 released. Fixed #10 javac: binary operator adds erroneous cast on 1st operand.

8 Sep 2013. Eclipse plugin version 0.3 released. Removed copypasta from Eclipse Compiler. Plugin should be more steady agains compiler changes.

14 May 2013. IntelliJ IDEA IDE plugin v0.2.1 with IDEA Ultimate Edition support.

17 Apr 2013. IntelliJ IDEA IDE plugin v0.2.

26 Nov 2012. Version 0.2 released. New feature: Assignment operator overloading via static #valueOf method.


javac, ant, etc

Just add to classpath: javac8-oo-plugin.jar for JDK8 or javac-oo-plugin.jar for JDK7.

javac -cp javac8-oo-plugin.jar 

Demo at examples/

Eclipse IDE update site

Click in menu:

Help - Install New Software
. Enter in
Work with

Tested on Eclipse Standard 4.3.2. Should work with older versions too.
To work on 4.4+ you need to install Scala IDE plugin (or similar plugin with Equanox weaving). You can find it in

Help -> Eclipse Marketplace
. This is workaround until normal solution will be found. Tested on 4.4 and 4.6.

Netbeans IDE

  1. Add javac-oo-plugin.jar as compile or processor library to Netbeans.
  2. Enable "Annotation Processing in Editor":
    Project Properties -> Build -> Compiling

Tested on 7.2.1


  1. Install Java Operator Overloading support plugin:
    File -> Settings -> Plugins -> Browse repositories
    . Mirror: idea-oo-plugin.jar)
    For Maven projects installation is done. IDEA should setup everything according to pom.xml.
    For other project types:
  2. Add javac8-oo-plugin.jar as compile or processor library.
  3. Enable Annotation Processing:
    Menu File -> Settings -> Compiler -> Annotation Processing -> Enable annotation processing
  4. Make sure you use
    compiler in
    Settings -> Java Compiler -> Use compiler
    Tested on IDEA 2019.2.4 Ultimate & Community editions. You can use earlier plugin versions for older IDEA releases.

Android project in IDEA 12

Add javac-oo-plugin.jar to

File - Settings - Compiler - Annotation Processors - Processor path

Android Studio (IDEA 13) / Gradle

add to

repositories {
    maven { url '' }
dependencies {
    compile 'java-oo:javac-oo-plugin:0.5'


Look at javac-oo-mvndemo/pom.xml


Read the paper to learn more. Supported operators (operator to method name map):


| +        | add        |
| -        | subtract   |
| *        | multiply   |
| /        | divide     |
| %        | remainder  |
| &        | and        |
| |        | or         |
| ^        | xor        |
| <<       | shiftLeft  |
| >>       | shiftRight |

If left operand has no such method then the plugin will try to use 'reverse' method

on right operand. So

will be transformed to
has such method.


| -        | negate     |
| ~        | not        |


| , >= | compareTo  | example: `a < b` <=> `a.compareTo(b)<0`
`==` and `!=` are not overloadable because it will break things


| []  | get       | `v = lst[i]` <=> `v = lst.get(i)`
| []= | set, put  | `map[s] = v` <=> `map.put(s,v)`,  `lst[i] = v` <=> `lst.set(i,v)`


| var = expr | var = VarClass.valueOf(expr) |


is not assignable to
is an instance of
has type
and there are static method

var = expr
is transformed to
var = VarClass.valueOf(expr)
. example:
BigInteger a = 1
is transformed to
BigInteger a = BigInteger.valueOf(1)

These methods exists in many java classes (example: BigInteger, BigDecimal) so you can use operators on them "out of the box". Or you can add these methods to your classes to use OO (see examples/

Subprojects / Implementation details

  • javac-oo-plugin

    • Plugin to JavaC 1.7 and Netbeans IDE for operator overloading. Based on javac-oo.
    • Building via maven at top level:
      cd java-oo; mvn clean install
      . Or import maven settings in your IDE.
  • eclipse-oo-plugin

  • idea-oo-plugin

    • IntelliJ IDEA IDE plugin for OO support.
    • Modify Java frontend in IDEA to allow OO. Need javac-oo-plugin to actually compile.
    • Build in IDEA. Run as IDEA plugin.
  • by-products:

    • javac-oo
      • Patched version of JavaC 1.7 for Operator Overloading support. If you need standalone javac compiler with OO.
      • Build via ant or netbeans:
    • eclipse-oo
      • Eclipse Java Developer Tools fork for Operator Overloading.
      • Use it if you need native Eclipse IDE support, or Eclipse Java Compiler support.
      • Build in Eclipse with PDE. Run as Eclipse application.


"Java Modular Extension for Operator Overloading", IJPLA, April 2014.

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