Java SDG Slicer

A program slicer for Java, based on the system dependence graph (SDG). Program slicing is a software analysis technique to extract the subset of statements that are relevant to the value of a variable in a specific statement (the slicing criterion). The subset of statements is called a slice, and it can be used for debugging, parallelization, clone detection, etc. This repository contains two modules:

sdg-core, a library that obtains slices from Java source code via the SDG, a data structure that represents statements as nodes and their dependencies as arcs.
sdg-cli, a command line client for sdg-core, which takes as input a Java program and the slicing criterion, and outputs the corresponding slice.

Warning: all method calls must resolve to a method declaration. If your Java program requires additional libraries, their source code must be available and included in the analysis with the -i option. Any method call that cannot be resolved will result in a runtime error.

Quick start

Build the project

JavaSDGSlicer manages its dependencies through maven, so you need to have the JDK (≥11) and Maven installed, then run

mvn package

A fat jar containing all the project's dependencies can be then located at ./sdg-cli/target/sdg-cli-{version}-jar-with-dependencies.jar.

Slice a Java program

The slicing criterion can be specified with the flag -c {file}#{line}:{var}[!{occurrence}, where the file, line and variable can be specified. If the variable appears multiple times in the given line, an occurrence can be set (append :2 to select the second occurrence).

If we wish to slice following program with respect to variable sum in line 11,

public class Example {
    public static void main(String[] args) {
        int sum = 0;
        int prod = 0;
        int i;
        int n = 10;
        for (i = 0; i < 10; i++) {
            sum += 1;
            prod += n;
        }
        System.out.println(sum);
        System.out.println(prod);
    }
}

The program can be saved to Example.java, and the slicer run with:

java -jar sdg-cli.jar -c Example.java#11:sum -t SDG

A more detailed description of the available options can be seen with:

java -jar sdg-cli.jar --help

A note on third party libraries

Our slicer requires the input Java program to be compilable, so all libraries must be provided using the -i flag. For the cases where the source code is not available, you may include the required libraries in the Java classpath by using the following call:

java -cp sdg-cli.jar:your-libraries.jar es.upv.slicing.cli.Slicer -c Example.java#11:sum -t SDG

This approach produces lower quality slices, as the contents of the library calls are unknown.

Library usage

A good usage example of sdg-core to obtain a slice from source code is available at Slicer.java#slice(), where the following steps are performed:

JavaParser is configured to (a) resolve calls in the JRE and the user-defined libraries, and to (b) ignore comments.
The user-defined Java files are parsed to build a list of CompilationUnits.
The SDG is created based on that list. The kind of SDG created depends on a flag.
A SlicingCriterion is created, from the input arguments, and the slice is obtained.
The slice is converted to a list of CompilationUnit (each representing a file).
The contents of each CompilationUnit are dumped to their corresponding file.

If the graph is of interest, it can be outputted in dot or PDF format via SDGLog#generateImages(), as can be seen in PHPSlice.java#124 (this class presents a frontend for an unreleased web Java slicer).

Missing Java features

Object-oriented features: abstract classes, interfaces, class, method and field inheritance, anonymous classes, lambdas.
Parallel features: threads, shared memory, synchronized methods, etc.
Exception handling: finally, try with resources.