org.ijsberg.iglu.util.logic
Class Expression

java.lang.Object
  org.ijsberg.iglu.util.logic.LogicalElement
      org.ijsberg.iglu.util.logic.Statement
          org.ijsberg.iglu.util.logic.Expression

public class Expression
extends Statement

Logical expression, composed of statements and subexpressions that may be evaluated.

An expression that has been analyzed fully, contains 1 operator and a number of elements that may be evaluated accordingly.

Field Summary

Fields inherited from class org.ijsberg.iglu.util.logic.Statement

statement

Fields inherited from class org.ijsberg.iglu.util.logic.LogicalElement

AND, NONE, NOT, operatorStr, OR

Constructor Summary

Expression(String expression)
Constructs an expression based on a logical expression defined in a string.

Expression(String expression, boolean useCache)
Constructs an expression based on a logical expression defined in a string.

Method Summary

static void	clearCache() Clears static expression cache.
static int	findEndOfSubExpression(String expression, int start) Finds the position of the end bracket ')' matching a start bracket '('.
int	getNrofElements()
String	getStatement() Performance optimizer: getStatement() in combination with isSingleStatement() isolates a single statement that can be evaluated immediately.
boolean	isSingleStatement()
boolean	match(Object[] statements) Answers questions like: does "r|w|x" match {"r","x"} (true). does "r|w&x" contain {"r","x"} (true). does "r|w&x" contain {"r"} (true). does "r|w&x" contain {"x"} (false).
boolean	match(String statement) Answers questions like: does "r|w|x" match "x" (true). does "r|w&x" match "x" (false).
String	toString()

Methods inherited from class java.lang.Object

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

Constructor Detail

Expression

public Expression(String expression)

Constructs an expression based on a logical expression defined in a string. The string may contain

• statements (which are not interpreted, just stored in Statement objects)
• logical operators '!'=NOT followed by an element,
• '|': OR inbetween 2 elements,
• '&': AND inbetween 2 elements,
• '(' and ')': group a subexpression

Parameters:

expression -

See Also:

Statement

Expression

public Expression(String expression,
                  boolean useCache)

Constructs an expression based on a logical expression defined in a string. The string may contain

• statements (which are not interpreted, just stored in Statement objects)
• logical operators '!'=NOT followed by statement,
• '|': OR inbetween 2 statements,
• '&': AND inbetween 2 statements,
• '(' and ')': group a subexpression

Using the cache is only recommended for expressions that are used as constants

Parameters:

expression -

useCache - expressions will be cached in a static cache if true

See Also:

Statement

Method Detail

findEndOfSubExpression

public static int findEndOfSubExpression(String expression,
                                         int start)

Finds the position of the end bracket ')' matching a start bracket '('.

Parameters:

expression -

start - position of the start bracket

Returns:

position of the matching end bracket or 0 if it can not be located

match

public boolean match(String statement)

Answers questions like:

• does "r|w|x" match "x" (true).
• does "r|w&x" match "x" (false).

Parameters:

statement -

Returns:

true if the expression logically matches the statement

match

public boolean match(Object[] statements)

Answers questions like:

• does "r|w|x" match {"r","x"} (true).
• does "r|w&x" contain {"r","x"} (true).
• does "r|w&x" contain {"r"} (true).
• does "r|w&x" contain {"x"} (false).

Overrides:

match in class Statement

Parameters:

statements -

Returns:

true if the expression logically matches the statement

toString

public String toString()

Overrides:

toString in class Statement

Returns:

a representation of the parsed expression tree

clearCache

public static void clearCache()

Clears static expression cache.

getNrofElements

public int getNrofElements()

Returns:

the number of logical elements this expression contains (not the grand total)

isSingleStatement

public boolean isSingleStatement()

Returns:

true if this expression contains one single statement (is therefor not composed)

getStatement

public String getStatement()

Performance optimizer: getStatement() in combination with isSingleStatement() isolates a single statement that can be evaluated immediately.

Overrides:

getStatement in class Statement

Returns:

the first statement string found