Java to JavaScript (java2js)
java2js
can translate simple Java programs to JavaScript and runs them using a JavaScript based JDK.
I made significant improvements to the 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 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 retro game engine library, which is web based.
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
await jdk.init(root)
- 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'
This function imports much of the standard Java lang classes into the global scope. You must use it before translating or running files.
await 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.
Features
- imports
- static classes
- static methods
- array literals
- arrays with initial size
- two dimensional arrays
- lambda arrow functions
- triple quotes
Known limitations
-
not very good error reporting
-
casting to int (truncation) 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
-
no method can be named
.length()
because it will be replaced with.length
for getting the length of Strings in JS
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!