j2swift

A Java to Swift syntax converter (still a work in progress).

Table of Contents

• Why?
• Versions
• Install
• General Process
• When It Crashes
• Ignored Code
• Covered Syntax
  • Classes
  • Interfaces
  • Enums
  • Fields
  • Methods
  • Constructors

Why?

When you're writing giant Android apps, you really don't want to spend time going through the trouble of converting your non-Android-API code into non-iOS-API code line by laborious line. In this process, you not only waste enormous effort, you also waste an enormous amount of time that you could be using to add even more functionality to your app! Thus, a tool is desperately needed to make this process quicker and virtually painless so that you can go back to more important matters. Google already began working on a solution to this problem in 2012 with j2objc. However, with the release of the Swift language in 2014, another tool is now needed to translate Java code to Swift code. j2swift hopes to accomplish this task through the use of the antlr4 parser generator. Since semantics is a matter that should be left mostly to the user, j2swift focuses mostly on syntax conversion.

Versions

For now, j2swift converts Java 8 syntax (https://github.com/antlr/grammars-v4/blob/master/java8/Java8.g4) to Swift 1.2 syntax.

Install

First follow these instructions on installing the antlr4 library. Then, you can install and run the tool on the test file as follows:

$ git clone https://github.com/eyob--/j2swift.git
$ cd j2swift/src/
$ javac com/j2swift/*.java
$ java com.j2swift.J2Swift ../Test.java

General Process

The program accepts a single java file as the argument for the program and writes the converted program into a file with name "[original filename].swift"

When It Crashes

If there is no Swift equivalent of an important section of code, the program will tell the user so in stderr and exit with a status of 1. This is the list of things which will cause a crash:

• Non-translatable modifiers
  • abstract
  • strictfp
  • transient
  • volatile
  • native
  • synchronized
  • default
• Type Parameter Quirks
  • additional bound "&"
  • wildcard "?"
• C-Style array declaration
• Receiver parameter
• Enum discrepancies
  • Any body declaration other than the constant list

Ignored Code

Sometimes, it may be more reasonable to simply skip a section of code instead of terminating the entire translation process so that the user can delete just those lines and feed the program back into the translator. This is the list of things which will be ignored and skipped by the translator:

• Annotations
  • declarations
  • regular usage

Covered Syntax

For an actual example of what j2swift covers for now, check Test.java and Test.java.swift

Classes

• Class modifiers
  • protected -> internal or private (user is asked)
• Type parameters
• Superclass and implemented interfaces

Interfaces

• Interface modifiers
• Type parameters
• Parent interfaces

Enums

• Enum (class) modifiers
• Implemented interfaces
• Constant list

Fields

• Field modifiers (class and interface)
  • the "final" modifier will cause the variable to be declared with "let"
• Variable declaration list
  • without initialization of variables
  • type declarations included (e.g. "var a: Int32")

Methods

• Method modifiers (class and interface)
• Type parameters
• Return value
• Formal Parameters
  • regular parameters
  • constant parameters
  • varargs
• Throws declaration

Constructors

• Constructor modifiers
• Type parameters
• Formal Parameters
  • regular parameters
  • constant parameters
  • varargs
• Throws declaration