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https://github.com/quinton-ashley/java2js
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110 lines
4.5 KiB
Markdown
110 lines
4.5 KiB
Markdown
# Java to JavaScript (java2js)
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java2js can translate simple Java programs to JavaScript and runs them using a JavaScript based JDK in the browser without the use of a VM on a server.
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[Try it out!](https://quinton-ashley.github.io/java2js/) The demo files are located in the docs folder of this repository, its a barebones implementation that shows what is possible with java2js.
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## Java classes included in the java2js JDK
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| `java.io` | | |
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| :-------- | ----------- | ----------- |
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| File | InputStream | PrintStream |
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| `java.lang` | | |
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| :---------- | ------------- | --------- |
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| Boolean | Byte | Character |
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| Double | Exception | Float |
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| Integer | Long | Short |
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| String | StringBuilder | System |
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| Thread | | |
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| `java.security` |
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| :-------------- |
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| MessageDigest |
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| `java.time` |
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| :---------- |
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| Instant |
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| `java.util` | | |
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| :----------------- | ---------------------- | ----------- |
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| AbstractCollection | AbstractList | AbstractMap |
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| AbstractSet | ArrayList | Arrays |
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| Collections | Formatter | HashMap |
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| HashSet | IllegalFormatException | Itr |
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| LinkedList | Random | Scanner |
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| Set | Stack | |
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## Features
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The java2js transpiler supports:
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- imports
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- primitive type casting
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- static classes
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- static methods
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- array literals
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- arrays with initial size
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- two dimensional arrays
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- lambda arrow functions
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- triple quote strings
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- try/catch blocks
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## API
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### await jdk.init(root)
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This function imports the standard java.lang classes into the global scope. You must use it before translating or running files.
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- 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://quinton-ashley.github.io/java2js/jdk'
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### await jdk.transpile(javaFile)
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Translates a Java class and loads it.
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- javaFile: a String with a Java class in it
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returns a String with the JavaScript transpilation of the Java class
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### jdk.run(jvmArgs)
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Runs the main method
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- jvmArgs: (optional) String array of JVM arguments.
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### jdk.workerPath
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java2js might cause the main thread to stall when transpiling a large Java file. This can cause your website to appear unresponsive/frozen. You can (optionally) utilize the java2js worker script to transpile Java asynchronously in a seperate JS thread. However due to CORS security 'jav2js_worker.js' must be hosted on your own domain, define 'jdk.workerPath' to be the location of that file.
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By default workerPath is undefined unless you are using java2js on a local server, in that case workerPath is the path to 'jav2js_worker.js' in the parent folder of jdk.root
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## Known limitations
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- not very good error reporting
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- 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
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- no support for private/public methods yet, though this could be done since they are included in modern JavaScript classes
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- no three dimensional arrays
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- no third level static classes
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- no method can be named `.length()` because it will be replaced with `.length` for getting the length of Strings in JS
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## Why did you make this?
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I created this package so intro level computer science students could write Java code but still use my [QuintOS](https://quintos.org) retro game engine library, which is web based.
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## Credits
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This project builds upon the [java-to-javascript](https://github.com/wyattades/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](https://github.com/java2script/java2script) by @BobHanson, @zhourenjian, @abego, and others.
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## Contribute
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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!
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## Commercial Use
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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`.
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