To help you identify problems early, your code is checked against the JRE emulation library whenever you run in development mode. Tip: You will save yourself a lot of frustration if you make sure that you use only translatable classes in your client-side code from the very beginning. To find out exactly which classes and methods are supported for core Java runtime packages, see the GWT JRE Emulation Reference. GWT supports only a small subset of the classes available in the Java 2 Standard and Enterprise Edition libraries, as these libraries are quite large and rely on functionality that is unavailable within web browsers. GWT does not support the strictfp keyword and can not ensure any particular degree of floating-point precision in translated code, so you may want to avoid calculations in client-side code that require a guaranteed level of floating-point precision. Strict Floating-Point: The Java language specification precisely defines floating-point support, including single-precision and double-precision numbers as well as the strictfp keyword. getName().įinalization: JavaScript does not support object finalization during garbage collection, so GWT is not able to be honor Java finalizers in production mode. However, it is possible to query an object for its class name using Object.getClass(). This and other optimizations preclude general support for reflection. Reflection: For maximum efficiency, GWT compiles your Java source into a monolithic script, and does not support subsequent dynamic loading of classes. The compiler will ignore the synchronized keyword but will refuse to compile your code if the Object’s related synchronization methods are invoked. Synchronization-related library methods are not available, including Object.wait(), Object.notify(), and Object.notifyAll(). Multithreading and Synchronization: JavaScript interpreters are single-threaded, so while GWT silently accepts the synchronized keyword, it has no real effect.
The GWT compiler removes and ignores all assertions by default, but you can enable them in production mode by specifying the -ea flag to Compiler. This is because the nature of the underlying JavaScript exception cannot be reliably mapped onto the appropriate Java exception type.Īssertions: assert statements are always active in development mode because it’s a great way for GWT libraries to provide lots of helpful error checking while you’re debugging. Instead, a JavaScriptException is produced for any implicitly generated exceptions. Note: Several fundamental exceptions implicitly produced by the Java VM, most notably NullPointerException, StackOverflowError, and OutOfMemoryError, do not occur in production mode as such. Additionally, long primitives cannot be used in JSNI code because they are not a native JavaScript numeric type.Įxceptions: try, catch, finally and user-defined exceptions are supported as normal, although Throwable.getStackTrace() is not meaningfully supported in production mode. Heavy use of long operations will have a performance impact due to the underlying emulation. Overflow is emulated to match the expected behavior. As of GWT 1.5, long primitives are emulated as a pair of 32-bit integers, and work reliably over the entire 64-bit range.
#LATEST JRE FULL#
Prior to GWT 1.5, the long type was was simply mapped to the integral range of a 64-bit JavaScript floating-point value, giving long variables an actual range less than the full 64 bits. long: JavaScript has no 64-bit integral type, so long needs special consideration.Integer division is implemented to explicitly round to the correct value. Operations on float are performed as double and will result in more-than-expected precision. Instead, the resulting value will outside of the legal range for that data type. Primarily, that means overflowing an integral data type ( byte, char, short, int) will not wrap the underlying value as Java specifies. All Java primitive numeric types (except for long, see below), are therefore implemented in production mode as if on doubles. Arithmetic: In JavaScript, the only available numeric type is a 64-bit floating point value.are all supported, with a couple of caveats. Intrinsic types: Primitive types ( boolean, byte, char, short, int, long, float, and double), Object, String, arrays, user-defined classes, etc. It is important to remember that the target language of your GWT application is ultimately JavaScript, so there are some differences between running your application in development mode and production mode (previously known as hosted mode and web mode, respectively): (Previous versions supported lower Java versions, see the Release Notes for more information.) GWT supports most of the core Java language syntax and semantics, but there are a few differences you will want to be aware of. Classes that provide similar functionality.Differences between JRE and emulated classes.
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