JevaES: Java Evaluator --- Expressions & Statements

prerelease version of 1998.12.2
Copyright (c) 1997, 1998 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.

JevaES accepts Java 1.1 source code expressions and statements (but not class declarations) and evaluates (interprets) them. JevaES uses the reflective capabilities included in Java 1.1 (java.lang.reflect) so it can be useful for exploring with and/or debugging an existing compiled system (in case your development environment doesn't provide this capability). The reflection API restricts access to public fields and methods, so it may not be able to access everything a debugging evaluator can.

JevaESUI is a user interface to JevaES. JevaESUI's window contains a scrolling pane of results and a field to type or paste in new expression or statements. A button starts evaluating the field as a Java expression (another just parses the expression); similar buttons do the same for Java statements.

The results can be examined using a Java Examiner, Jexa, which uses the Java 1.1 reflection capabilities and the JavaBeans introspector to access the public fields and properties of objects and display them in an outline tree for browsing. Objects found through navigation can be used to set the value of Jexa.mousedObject, so that they are accessible for use in method calls.

Applet: If you're viewing this page in a fully Java 1.1 capable browser such as Communicator 4.06, IE 4.01, or HotJava, pressing the button applet below should start up JevaESUI's window. If your browser does not support Java 1.1, loading the applet will cause an error and no button will appear. (It may take a few minutes to load the files over the network and start the applet.) [On MIT Athena Suns, add javadev, then hotjava.] You can also point the Sun's JDK appletviewer at the URL of this page to run the applet button
(appletviewer http://www.ai.mit.edu/people/caroma/tools/JevaESUI.html);
appletviewer won't display this surrounding text.

Type or paste expressions or statements in the lower pane; results will appear in the upper pane. Variables declared at top level (not inside a { } block) extend the environment used for evaluating later expressions and statements. You can try complex (or ridiculous) parses like "~1*2+3^4%5|6&7>>>8" and examine the resulting parse tree to see if you understand the precedence order. You can Print to the result pane with:

  import edu.mit.ai.psg.jevaESUI.JevaESUI;
  JevaESUI.out.println("Hello.");

(If used in an application rather than from an applet's security box, JevaESUI redirects System.out to the result pane as well.) Previous results are in: JevaESUI.results.elementAt(n)

Use from programs: To use JevaESUI for your own Java1.1 experiments (e.g., loaded along with your own programs so you can experiment with them directly without compiling), download the Jar files at the end of this page and list them in your classpath. (JevaES requires Java 1.1.) At a point in your program where you want to experiment you can just import edu.mit.ai.psg.jevaESUI.JevaESUI and then call it:

  JevaESUI.main(null);

Alternatively, you can add insepection points into your program, where you can experiment with values of program variables using a read-eval-print-loop (REPL) window as shown in the brief example below. (To run example, copy text below and save it to DemoJevaESUIInspectPoint.java, then compile and run.)

  // DemoInspectPoint.java
  import java.awt.*;
  import edu.mit.ai.psg.jevaESUI.JevaESUI;
  import edu.mit.ai.psg.jevaES.JevaES;

  public class DemoInspectPoint {
    public static void main(String[] args) {

      Frame frame = new java.awt.Frame("DemoInspectPoint Frame");
      frame.add(new Label("Resize Me, then try frame.getSize()"));
      frame.setSize(500, 100);
      Dimension dim = frame.getSize();
      frame.show();

      JevaESUI.replWindow // inspectPoint
        (true, false, true,
         ("InspectPoint: \n"+
          "  frame: "+frame+"\n"+
          "  dim: "+dim+"\n"),
         JevaES.extendEnv
         (Frame.class, "frame", frame,
          JevaES.extendEnv
          (Dimension.class, "dim", dim,
           JevaES.makeDefaultEnv())));
    }
  }

Jar files: The current jar files can be downloaded here:

Prerelease JevaESUI1998-12-02.jar (or via ftp) (browse javadoc) (requires JevaES, Jexa)
Prerelease JevaES1998-12-02.jar (or via ftp) (browse javadoc)
Prerelease Jexa1998-12-02.jar (or via ftp) (browse javadoc)

Update Notes --- 1998-08-01: JevaES supports import, which makes working with programs in packages much easier. JevaESUI can be started with an environment parameter, which makes it more useful as a breakpoint. Jexa uses bean introspection in addition to reflection, which makes some nonpublic properties browsable through accessor methods. Jexa can set Jexa.mousedObject to a browsed object, so objects found through navigation can be used in method calls. Jexa can regenerate an outline for an object using any of the outline component generators that apply to the object. Packages were renamed using lowercase. Improvements to documentation. Miscellaneous bug fixes. 1998-08-07: JevaESUI leaves remainder of string after parsed expression or statement in lower pane, so it's possible to paste multiple statements or expressions into buffer and evaluate them one by one. When parse exceptions occur, JevaESUI highlights first erroneous token in pane. 1998-12-02: Bug fixes: Fixed bug in evaluating nested array initializers; import may now catch package name typos by checking directories in classpath (but feature is disabled in applet security sandbox) ; adjusted parser to parse semicolons with preceding expression statements; etc. 1998-12-02: JevaESUI.repl(..) allows the user to return values and throw exceptions, so it can be used in stubs to pop up a window for the user to implement.

Platform Notes: Using Netscape Communicator 4.06 enhances security which prevents the Java bean Introspector from doing its analysis, so when called from an applet in Communicator 4.06, Jexa will only display public fields of objects. Note that for some versions of Communicator, "Save Link As" may not download jar files correctly from the via http link, so try the via ftp link instead.

Prior version of this page with prior platform notes and prior versons of software is available here.

Bugs to jeva-bugs@ai.mit.edu

CarlManning

caroma@ai.mit.edu

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This page describes research done at the Artificial Intelligence Laboratory of the Massachusetts Institute of Technology. Support for this research was provided in part by the Advanced Research Projects Agency of the Department of Defense under contracts MDA972-95-1-0018 (North East Regional Consortium Grant) and N66001-95-C-8611 (Computer Aided Education and Training Initiative), and the MIT Department of Electrical Engineering and Computer Science. Support for this research has also been received from IBM, which has generously donated Thinkpad pen computers, and from Microsoft, which has generously donated software.