java2js/README.md

# Java to Javascript

I've built on top of the [java-to-javascript](https://github.com/wyattades/java-to-javascript) transpiler by @wyattades and got inspiration from the barebones JDK (Java Development Kit) implementation in [java2javascript](https://github.com/java2script/java2script) by @BobHanson, @zhourenjian, @abego, and others.

I created this project so intro level computer science students could write Java code but still use my [QuintOS](https://github.com/quinton-ashley/quintos) retro game engine library, which is web based. Yes, I went to all this trouble just so my students don't have to run their programs in a boring Java console! To achieve this I've been working on a JDK implementation in modern Javascript.

## Java Classes Included in the JS JDK

| java.io |             |             |
| ------- | ----------- | ----------- |
| File    | InputStream | PrintStream |

| java.lang |               |           |
| --------- | ------------- | --------- |
| Boolean   | Byte          | Character |
| Double    | Exception     | Float     |
| Integer   | Long          | Short     |
| String    | StringBuilder | System    |
| Thread    | Throwable     |           |

| java.security |     |     |
| ------------- | --- | --- |
| MessageDigest |     |     |

| java.time |     |     |
| --------- | --- | --- |
| Instant   |     |     |

| java.util          |                        |             |
| ------------------ | ---------------------- | ----------- |
| AbstractCollection | AbstractList           | AbstractMap |
| AbstractSet        | ArrayList              | Arrays      |
| Collections        | Formatter              | HashMap     |
| HashSet            | IllegalFormatException | Itr         |
| LinkedList         | Random                 | Scanner     |
| Set                | Stack                  |             |

## API

### jdk.init(root)

- root (optional) can be a local path or url to the parent folder of the JS `jdk` folder, by default it links to 'https://unpkg.com/java2js' (this package) so you don't need to change it

This function imports much of the standard Java lang classes into the global scope. You must use it before translating or running files.

### jdk.translate(javaFile)

- javaFile is a string with contents of a Java file

returns the Java file translated into JavaScript

### jdk.load(translatedJSFile)

- translatedJSFile is the translated JS class to run

Loads the JS class file but doesn't run the main method.

### jdk.run(jvmArgs)

Runs the main method with optional JVM arguments.

## Known limitations

- casting to int truncation workaround requires parenthesis around the number being cast `int x = (int) (Math.random() * 100);`

- no support for method overloading, though a workaround might be possible by making a function with the og name route to each of the variations of the overloaded function

- no support for private/public methods yet, though this could be done since they are included in modern JavaScript classes

- no three dimensional arrays

- no third level static classes

- not much error checking

## Contribute

I've only done a partial implementation of the Java 17 JDK in JavaScript, so if you're interested in adding more please go for it and submit a pull request!