edu.sdsc.inca.util
Class ExprEvaluator

java.lang.Object
  edu.sdsc.inca.util.ExprEvaluator

public class ExprEvaluator

extends java.lang.Object

A simple top-down boolean expression evaluator. Supports the boolean binary operators <, <=, >, >=, ==, !=, <>, &&, and ||, as well as perl's pattern match (=~) and mismatch (!~) operators. Supports parenthesized sub-expressions. Operands may be any of: a quoted string literal; a numeric literal; a pattern literal enclosed in slashes; an identifier defined in the report body by an ID tag; a version literal composed of digits, letters, underscores and dots.

Author:

jhayes

Field Summary

static java.lang.String	FAIL_EXPR_FAILED Failure result values from eval.
static java.lang.String	FAIL_INVALID_OPERATOR
static java.lang.String	FAIL_MISSING_OPERAND
static java.lang.String	FAIL_MISSING_OPERATOR
static java.lang.String	FAIL_MISSING_RPAREN
static java.lang.String	FAIL_UNDEFINED_SYMBOL
protected static java.util.regex.Pattern	OPERAND_PATTERN Operands: a quoted or slash-surrounded literal or a symbol.

Constructor Summary

ExprEvaluator()

Method Summary

protected static java.lang.String	binary(java.lang.StringBuffer expr, java.util.Properties symbols, java.lang.String valueIfUndef) Part of a simple top-down expression evaluator.
protected static java.lang.String	conjunction(java.lang.StringBuffer expr, java.util.Properties symbols, java.lang.String valueIfUndef) Part of a simple top-down expression evaluator.
static java.lang.String	eval(java.lang.String expr, java.util.Properties symbols, java.lang.String valueIfUndef) Evaluate a boolean expression given a set of symbols.
protected static java.lang.String	getOperand(java.lang.StringBuffer expr) Part of a simple top-down expression evaluator.
protected static java.lang.String	parenthesized(java.lang.StringBuffer expr, java.util.Properties symbols, java.lang.String valueIfUndef) Part of a simple top-down expression evaluator.
protected static void	skipSpaces(java.lang.StringBuffer sb) Removes leading spaces from a StringBuffer.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

FAIL_EXPR_FAILED

public static java.lang.String FAIL_EXPR_FAILED

Failure result values from eval.

FAIL_INVALID_OPERATOR

public static java.lang.String FAIL_INVALID_OPERATOR

FAIL_MISSING_OPERAND

public static java.lang.String FAIL_MISSING_OPERAND

FAIL_MISSING_OPERATOR

public static java.lang.String FAIL_MISSING_OPERATOR

FAIL_MISSING_RPAREN

public static java.lang.String FAIL_MISSING_RPAREN

FAIL_UNDEFINED_SYMBOL

public static java.lang.String FAIL_UNDEFINED_SYMBOL

OPERAND_PATTERN

protected static java.util.regex.Pattern OPERAND_PATTERN

Operands: a quoted or slash-surrounded literal or a symbol.

Constructor Detail

ExprEvaluator

public ExprEvaluator()

Method Detail

eval

public static java.lang.String eval(java.lang.String expr,
                                    java.util.Properties symbols,
                                    java.lang.String valueIfUndef)

Evaluate a boolean expression given a set of symbols.

Parameters:

expr - the expression to evaluate

symbols - a table that associates symbol names with values

valueIfUndef - the value to use for identifiers encountered in the expression that have no value in the symbol table. If null, the method throws an exception when it encounters an undefined symbol.

Returns:

null if the expression is true; otherwise, a failure message that consists of one of the result values above optionally followed by a colon and a space-delimited set of symbols participating in the failure

conjunction

protected static java.lang.String conjunction(java.lang.StringBuffer expr,
                                              java.util.Properties symbols,
                                              java.lang.String valueIfUndef)

Part of a simple top-down expression evaluator. This precedence level strips and evaluates the left-associative && and || operators.

Parameters:

expr - the expression to evaluate

symbols - a table that associates symbol names with values

valueIfUndef - the value to use for identifiers encountered in the expression that have no value in the symbol table. If null, the method throws an exception when it encounters an undefined symbol.

Returns:

null if the expression is true; otherwise, a failure message that consists of one of the result values above optionally followed by a colon and a space-delimited set of symbols participating in the failure

parenthesized

protected static java.lang.String parenthesized(java.lang.StringBuffer expr,
                                                java.util.Properties symbols,
                                                java.lang.String valueIfUndef)

Part of a simple top-down expression evaluator. This precedence level strips and evaluates parenthesized sub-expressions.

Parameters:

expr - the expression to evaluate

symbols - a table that associates symbol names with values

valueIfUndef - the value to use for identifiers encountered in the expression that have no value in the symbol table. If null, the method throws an exception when it encounters an undefined symbol.

Returns:

null if the expression is true; otherwise, a failure message that consists of one of the result values above optionally followed by a colon and a space-delimited set of symbols participating in the failure

binary

protected static java.lang.String binary(java.lang.StringBuffer expr,
                                         java.util.Properties symbols,
                                         java.lang.String valueIfUndef)

Part of a simple top-down expression evaluator. This precedence level strips and evaluates the binary operations <, <=, >, >=, ==, !=, <>, =~, and !~.

Parameters:

expr - the expression to evaluate

symbols - a table that associates symbol names with values

valueIfUndef - the value to use for identifiers encountered in the expression that have no value in the symbol table. If null, the method throws an exception when it encounters an undefined symbol.

Returns:

null if the expression is true; otherwise, a failure message that consists of one of the result values above optionally followed by a colon and a space-delimited set of symbols participating in the failure

getOperand

protected static java.lang.String getOperand(java.lang.StringBuffer expr)

Part of a simple top-down expression evaluator. This precedence level strips and returns operands.

Parameters:

expr - the expression to evaluate

Returns:

the operand at the beginning of the expression; null if none

skipSpaces

protected static void skipSpaces(java.lang.StringBuffer sb)

Removes leading spaces from a StringBuffer.

Parameters:

sb - the string buffer to trim