Java to JavaScript (java2js)
java2js can translate simple Java programs to JavaScript and runs them using a JavaScript based JDK.
Try it out! The demo files are located in the docs folder of this repository, its a barebones implementation that shows what is possible with java2js.
Java classes included in the java2js 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 |
Features
The java2js transpiler supports:
- imports
- primitive type casting
- static classes
- static methods
- array literals
- arrays with initial size
- two dimensional arrays
- lambda arrow functions
- triple quote strings
API
await jdk.init(root)
This function imports the standard java.lang classes into the global scope. You must use it before translating or running files.
- root: (optional) path to the JS JDK folder, by default it is
./jdk(the java2js JS JDK), for online use on codepen or similar code sharing sites you can use this link as the root path: 'https://unpkg.com/java2js/jdk'
await jdk.transpile(javaFile)
Translates a Java class and loads it.
- javaFile: a String with a Java class in it
returns a String with the JavaScript transpilation of the Java class
jdk.run(jvmArgs)
Runs the main method
- jvmArgs: (optional) String array of JVM arguments.
Known limitations
-
not very good error reporting
-
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
-
no method can be named
.length()because it will be replaced with.lengthfor getting the length of Strings in JS
Why did you make this?
I created this package so intro level computer science students could write Java code but still use my QuintOS retro game engine library, which is web based.
Credits
This project builds upon the java-to-javascript transpiler by @wyattades. I also did a modern JS implementation of the fundamental classes in the JDK (Java Development Kit), which I got the inspiration to do from java2javascript by @BobHanson, @zhourenjian, @abego, and others.
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!
Commercial Use
This project is licensed under the copyleft GNU GENERAL PUBLIC LICENSE 3.0 (only) license. If you'd like to request legal permission to use this code in a commerical product or closed source project please email me (qashto@gmail.com) with a proposal of how you would like to use java2js.