# 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, 

```java=
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
```

## Library usage

A good usage example of `sdg-core` to obtain a slice from source code is available at [Slicer.java#slice()](/sdg-cli/src/main/java/tfm/cli/Slicer.java#L204), where the following steps are performed:

1. JavaParser is configured to (a) resolve calls in the JRE and the user-defined libraries, and to (b) ignore comments.
2. The user-defined Java files are parsed to build a list of `CompilationUnit`s.
3. The SDG is created based on that list. The kind of SDG created depends on a flag.
4. A `SlicingCriterion` is created, from the input arguments, and the slice is obtained.
5. The slice is converted to a list of `CompilationUnit` (each representing a file).
6. 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](/sdg-cli/src/main/java/tfm/cli/PHPSlice.java#L124) (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.