Package net.sourceforge.templat.expr

Lexes and parses an expression.

See:
Description

Interface Summary

Selector

Class Summary

ArraySubscript
ExprActions	Actions for ExprParser and IncludeParser.
Expression	Contains static methods to evaluate an expression within a template statement.
ExprLexer	Splits a string into tokens.
ExprLexer.Token	Represents a token returned by the enclosing ExprLexer.
ExprParser	Parses an expression.
MethodCall

Package net.sourceforge.templat.expr Description

Lexes and parses an expression.

This package is responsible for lexing and parsing an expression used in some template tags. An expression is a complicated structure to parse, so this task is offloaded from the TemplateLexer and the tokens into this package. The main entry point of this package is the Expression class.

The heart of this package is the expr.yacc source file (available in the source download, in src/net/sourceforge/templat/expr/expr.yacc). This is a standard yacc file, except it contains Java source instead of C source. This file is processed by BYACC/J, an open-source yacc implementation that produces parsers written in Java instead of parsers written in C. The output of this process is the ExprParser Java source file.

An expression is primarily just a variable, literal number, or class name, possibly with method calls and/or array subscripts. The expr.yacc file defines the exact grammar.

The parser (produced from the expr.yacc file) calls ExprLexer to get a stream of tokens representing the entire input expression string being parsed. Then each applicable rule in the expr.yacc grammar is applied; these rules call actions defined in the ExprActions class. The two actions of method call and array subscript are handled by the classes MethodCall and ArraySubscript.