mirror of
https://github.com/quinton-ashley/java2js
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94 lines
3.4 KiB
Markdown
94 lines
3.4 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.
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I made significant improvements to 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), inspired by [java2javascript](https://github.com/java2script/java2script) by @BobHanson, @zhourenjian, @abego, and others.
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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.
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## Java Classes Included in the JS 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 | Throwable | |
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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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## API
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### await jdk.init(root)
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- root (optional) path to the parent folder of the JS `jdk` folder, by default it is `./` you could also link to this package online 'https://unpkg.com/java2js'
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This function imports much of the standard Java lang classes into the global scope. You must use it before translating or running files.
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### await jdk.translate(javaFile)
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- javaFile is a string with contents of a Java file
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returns the Java file translated into JavaScript
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### jdk.load(translatedJSFile)
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- translatedJSFile is the translated JS class to run
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Loads the JS class file but doesn't run the main method.
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### jdk.run(jvmArgs)
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Runs the main method with optional JVM arguments.
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## Features
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- imports
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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 quotes
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## Known limitations
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- not very good error reporting
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- casting to int (truncation) requires parenthesis around the number being cast `int x = (int) (Math.random() * 100);`
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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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## 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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