JevaES: Java Evaluator --- Expressions & Statements

prerelease version of 1999.10.11
Copyright (c) 1997, 1998, 1999 Massachusetts Institute of Technology.
This software is provided "as is" without express or implied warranty.
Contains parser generated by Sun's JavaCC/JJTree from a modified version of the example Java grammar.

JevaESCLI is a command line interface to JevaES. It can optionally be used within a Gnu Emacs M-! or M-x shell as shown at right. (By default it reads from System.in, which cannot be used by multiple threads simultaneously, including debugger threads in jdb).

JevaESGUI is a graphical (windowed) user interface to JevaES. It creates a window for each invocation so it is possible to interact with multiple threads concurrently. It also highlights syntax errors. Editing is via mouse cut and paste. JevaESGUI can also be used as an applet; try the examples on its applet page.

The results of expressions can be examined using Jexa, the Java Examiner. In turn, objects found through navigation can be used to set the value of Jexa.mousedObject, so that they are accessible for use in method calls. (See applet page.)

Used as Applet: JevaESGUI can be used as an applet on a page. If there are other applets on the page, it can be used to interact with those applets. (See applet page.)

Called from programs: JevaES can be used to experiment with your own programs. The JevaESGUI read-eval-print-loop (REPL) can be invoked from programs which provide values of variables to inspect or manipulate. A JevaESGUI REPL can return values (or throw exceptions) back to programs, so it can be used in a program stub which asks the user to type in code to compute the result. JevaES can also be called directly (without either UI) to evaluate program-generated java expressions and statements.

See the jevaESUI package javadoc and jevaES package javadoc for more details.

Jeva (experimental)

1999-10-11: JevaES/Jeva docs: added example DemoEvalWithEnv.java demonstrating that parsing expressions takes an order of magnitude longer than evaluating, and illustrating how programs can evaluate the same expression many times without reparsing by using an environment to bind identifiers to different values. JevaES/Jeva: made error messages more consistent. Jeva: fixed inheritance of interface fields; fixed array parameter type in call to super method; fixed initialization when running from a class name (e.g., Jeva.runClass, Jeva.main) an interpreted class with interfaces; fixed initialization bug in an interpreted class which is also needed as its own method parameter type; to diagnose common installation bug, CompileUnit now issues a one-time warning to when javac class is not found in classpath and it has to fall back on slower out-of-process calls.

1999-07-05: Jeva: Fixed infinite loop bug reading java files that crept into the 1999-06-09 release.

1999-06-09: Jeva: Jeva's eval hook has been extended to be called after a construct's subexpressions have been evaluated, just before the construct is 'applied', for recording call traces; this required making the parse tree less flat for operators. CompileUnit.setTempRoot(..) can now be used to enable compiled proxy classes to be reused between sessions. Added Jeva.runClass(..). Shortened names of option bits in Jeva and JevaGUI. Bound localOut and localErr to the local output pane PrintWriters; bound localResults to access the results in JevaCLI, JevaESCLI, JevaGUI, and JevaESGUI. Fixed bugs in interpreted constructors with parameters of interpreted type, explicit constructor calls, method synchronization. JevaES and Jeva: Fixed bugs in casting, == (between reference values including null == ...), || and &&, accessibility of members of non-public classes; import by name now correctly overrides import on demand. Localization: JevaESUI and JevaUI may be localized; button and prompt strings are properties that may be overridden according to language of default locale for international use (however, JevaES error messages are not localizeable in this version).

1999-02-28: Package statements can be used to change the current package for access to package protected fields and methods. Java1.2 reflection permits access to non-public fields and methods (may require ReflectPermission). Jeva adds interpreted classes, evalhook to JevaES.

1998-12-02: compatible with Java 1.1.

Related Systems:

• Interpreting Java Source Code
  • Metamata Debug: a commercial Java debugger, implements Java 1.2 inside a debugger.
  • DynamicJava: A Java 1.2 source code interpreter in development. As in Jeva, it does not permit classes to be redefined. In addition, it implements top level procedure (static method) definitions.
  • BeanShell: a Java 1.0-like scripting language for developing JavaBeans; implements many Java expressions and statements, and adds its own dynamically typed script procedure objects.
• Protocol hooks for extending/modifying Java program behavior
  • OpenJava: Provides object-oriented mechanisms for implementing Java extensions by transforming the Java source code. "Compile-time reflection" enables extension transformations to introspect the classes involved (types, superclasses, interfaces, etc.). Via meta-classes, extension transformations can be customized on a per-class basis as well as a per-syntactic-construct basis.
  • metaXa (MetaJava): extends the Java Virtual Machine to provide events such as entering methods, reading fields, acquiring and releasing locks, etc., which are processed by meta-objects. Includes methods for binding meta-objects to objects, and for replacing method bytecodes.
• Parsing Java Source Code
  • JavaCC/JJTree by Sun's test division (now maintained by the spin off Metamata along with a redesigned version, MParse) was among the first Java parsers in Java available, and is used in Jeva/JevaES. It has some features not available in others, such as the ability to preserve comments. It is free, but not yet open-source.
  • JTB, a Java Tree Builder that works with JavaCC in place of JJTree. It is less flexible about what tree gets built from the grammar, but may provide cleaner access to nodes.
  • ANTLR, an open-source parser generator with a less Java-like grammar syntax.
  • SableCC builds parse trees with type-safe accessors for each child node. It generates LALR parsers, which some have reported are much harder to debug than recursive descent parsers such as JavaCC or ANTLR.
• Catalog of tools for Compiler construction with Java
• List of non-Java Programming languages for the Java Virtual Machine