A complete parser and interpreter for a subset of the Java language, written in Python. This was produced as a deliverable for my final year project for my degree in Computer Science from the University of Leicester - it is barely commented, and was written under deadlines without much aim for particularly excellent code. It was a project aimed at being interesting over all else - performance is no doubt abysmal.

This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.

You should have received a copy of the GNU General Public License along with this program. If not, see http://www.gnu.org/licenses/.

• Python 3.3

• Tokenizer (Lexical analysis).
• Parser (Syntax analysis).
• Semantic Analyser
• Interpreter
• Graphical Debugger
• Compiler (Targeting Python bytecode)

• init.py
• classes.py
• compiler.py
• debug.py
• exceptions.py
• interpreter.py
• library.py
• LICENSE
• parser.py
• README.md
• semantics.py
• tokenizer.py
• examples
  • Generics.java
  • Inheritance.java
  • MergeSorter.java
  • OperatorPrecedence.java
  • Simple.java
• mjast
  • init.py
  • components.py
  • core.py
  • expressions.py
  • node.py
  • primitive_types.py
  • promotable.py
  • statements.py
• stdlib
  • init.py
  • io.py
  • lang.py
  • util.py

The interpreter supports the full Middlewieght Java language, as defined in the the paper MJ: An imperative core calculus for Java and Java with effects, and some extensions, listed below:

• for loops.
• while loops.
• Operators.
• Multiple constructors.
• Empty blocks.
• Declaration with assignment.
• import statements (albeit with different behaviour to full Java).
• Using generic types/methods.
• if blocks without else blocks.
• else if blocks.
• Implied extends Object.
• Empty super() can be left out.
• Static classes & methods.
• Strings & string literals.
• Brackets for operation grouping.

Most of the Java standard library is unsupported. Some small parts have been implemented, and these are listed below:

• lang.Integer
• lang.String
• lang.System.out
• util.List
• io.PrintStream

Note that all of these implementations are partial (even skeletal).

Do note, however, that the interpreter does include a full system to allow the implementation of Python libraries for use in the interpreted code. This would allow full implementation of the standard library, given the time and effort.

The interpreter can be used simply as a command line application. Given Python 3.3 is installed, simply run python interpreter.py some_code.java (on some platforms, it may be necessary to use python3 to differentiate between Python 2.x and 3.x, which can be installed simultaneously. On Unix platforms, ./interpreter.py some_code.java should also work, given the code is set as executable.

Also included is a graphical debugger that allows stepping through code, and viewing the execution state. This is debug.py.

The compiler should work with python compiler.py some_code.java - note that it only handles an extremely small subset of the language.

The interpreter can be used as a library from other software, and the parser could also be used independantly to produce an abstract syntax tree that could be worked with as desired.

Written by Gareth Latty gareth@lattyware.co.uk as a deliverable for CO3016 Computer Science Project, part of a Computer Science degree at the Unversity of Leicester.