Skip to content


Switch branches/tags

Name already in use

A tag already exists with the provided branch name. Many Git commands accept both tag and branch names, so creating this branch may cause unexpected behavior. Are you sure you want to create this branch?

Latest commit


Git stats


Failed to load latest commit information.

Nopol Build Status Coverage Status

Nopol is an automatic software repair tool for Java. This code is research code, released under the GPL licence.

If you use this code for academic research, please cite: Nopol: Automatic Repair of Conditional Statement Bugs in Java Programs (Jifeng Xuan, Matias Martinez, Favio Demarco, Maxime Clément, Sebastian Lamelas, Thomas Durieux, Daniel Le Berre, Daniel Le Berre, Martin Monperrus). IEEE Transactions on Software Engineering, 2016.

 title = {Nopol: Automatic Repair of Conditional Statement Bugs in Java Programs},
 author = {Xuan, Jifeng and Martinez, Matias and Demarco, Favio and Clément, Maxime and Lamelas, Sebastian and Durieux, Thomas and Le Berre, Daniel and Monperrus, Martin},
 journal = {IEEE Transactions on Software Engineering},
 doi = {10.1109/TSE.2016.2560811},
 year = {2016},

Others papers about Nopol:

Getting started

Nopol requires Java and an SMT solver installed on the machine (e.g. Z3)

Up to commit 80130c4c, Nopol required Java 8. Now it also works on Java 11, see #214

  1. Compile NoPol:
git clone
cd nopol/nopol
export JAVA_HOME=/usr/lib/jvm/java-8-openjdk-amd64

# -DskipTests is required, to run the tests one needs to compile ../test-projects/ (see below)
mvn package -DskipTests
  1. Locate the Nopol jar file produced at step 1)
$ ls target/*jar
target/nopol-0.2-SNAPSHOT-jar-with-dependencies.jar # we use this one

In the following, nopol.jar refers to the jar file with dependencies (target/nopol-<VERSION>-SNAPSHOT-jar-with-dependencies.jar)

  1. Compile the test-projects
$ cd ../test-projects/
# compiling app (in target/classes) and tests (in target/test-classes), but don't run the tests (they obviously fail, because the goal is to repair them)
$ mvn test -DskipTests 

3b) Optional: run the tests of Nopol to check your installation

$ cd ../nopol/
$ mvn test
  1. Execute Nopol (parameters explained below)

(Long commands are broken in several lines, separated by a backslash, which means an escaped linebreak in Unix shells.)

cd ../test-projects/
java -jar nopol.jar \
-s src/main/java/ \
-c target/classes:target/test-classes:/home/<user>/.m2/repository/junit/junit/4.11/junit-4.11.jar:/home/<user>/.m2/repository/org/hamcrest/hamcrest-core/1.3/hamcrest-core-1.3.jar \
-t symbolic_examples.symbolic_example_1.NopolExampleTest \
-p ../nopol/lib/z3/z3_for_linux

If you keep nopol.jar instead of the actual jar located at the previous step, you'll get Error: unable to access jarfile nopol.jar (see above). You should replace also <user> by your own username.

It should output something like:

Nb classes : 34
Nb methods : 53
Nb statements: 5
Nb statement executed by the passing tests of the patched line: 0
Nb statement executed by the failing tests of the patched line: 0
Nb unit tests : 9
Nb Statements Analyzed : 3
Nb Statements with Angelic Value Found : 1
Nb inputs in SMT : 8
Nb SMT level: 2
Nb SMT components: [4] [== of arity: 2, != of arity: 2, < of arity: 2, <= of arity: 2]
                  class java.lang.Boolean: 4
Nb variables in SMT : 13
Nb run failing test  : [2, 1]
Nb run passing test : [4, 18]
NoPol Execution time : 3262ms
symbolic_examples.symbolic_example_1.NopolExample:12: CONDITIONAL index < 1

NoPol (SMT and Dynamoth) returns also a unix code (integer):

  • 0 if a patch has been found
  • -1 otherwise

Parameter -c can be found with mvn dependency:build-classpath.

Minimal Usage

4 parameters are required

Usage: java -jar nopol.jar

  (-s|--source) source1:source2:...:sourceN 
        Define the path to the source code of the project. For instance `src/main/java`

  (-c|--classpath) <classpath>
        Define the classpath of the project separated by a path separator (`:` on Linux). 
        Must contain the application binary classes (`target/classes`)
        Must contain the application test classes (`target/test-classes`)
        Must contain the library classes (`lib/junit.jar` for instance)
  [(-t|--test) test1:test2:...:testN ]
        Define the tests of the project. For instance `symbolic_examples.symbolic_example_1.NopolExampleTest`

  [(-p|--solver-path) <solverPath>]
        Define the solver binary path (only used with smt synthesis). For instance `../nopol/lib/z3/z3_for_linux`

Advanced Usage

See also notes below.

Usage: java -jar nopol.jar

  [(-m|--mode) <repair|ranking>]
        Define the mode of execution. (default: repair)

  [(-e|--type) <pre_then_cond|condition|precondition>]
        The type of statement to analyze (only used with repair mode). (default: pre_then_cond)

  [(-o|--oracle) <angelic|symbolic>]
        Define the oracle (only used with repair mode). (default: angelic)

  [(-y|--synthesis) <smt|dynamoth>]
        Define the patch synthesis. (default: smt)

  [(-l|--solver) <z3|cvc4>]
        Define the solver (only used with smt synthesis). (default: z3)

  [--complianceLevel <complianceLevel>]
        The Java version of the project. (default: 7)

  [--maxTime <maxTime>]
        The maximum time execution in minute for the whole execution of Nopol.(default: 10)

  [--maxTimeType <maxTimeType>]
        The maximum time execution in minute for one type of patch per per suspicious statement (eg. 5 minutes max to find a precondition at line x). (default: 5)

  [(-z|--flocal) < cocospoon|dumb|gzoltar>]
        Define the fault localizer to be used. (default: cocospoon). 
          "cocospoon" means source code instrumentation plus ochiai metric.
          "dumb" means random fault localization. 
          "gzoltar" means binary code instrumentation with external library plus ochiai metric.

Notes: For using Dynamoth (-y dynamoth), you must add tools.jar in the classpath of Nopol, and use java with -cp (and not -jar):

java -cp $JAVA_HOME/lib/tools.jar:../nopol/target/nopol-SNAPSHOT-jar-with-dependencies.jar <nopol arguments>

Examples of Real Bugs Targeted by Nopol:

Apache Commons Math:

Apache Commons Lang:

Google GSON:


For questions and feedback , please contact @monperrus


Automatic program repair system for Java based on dynamic analysis and code synthesis with SMT. Also contains the code of Dynamoth.








No releases published


No packages published