uk.ac.sheffield.vtts.model

Class Comparison

java.lang.Object

uk.ac.sheffield.vtts.model.Element

uk.ac.sheffield.vtts.model.Named

uk.ac.sheffield.vtts.model.Expression

uk.ac.sheffield.vtts.model.Function

uk.ac.sheffield.vtts.model.Predicate

uk.ac.sheffield.vtts.model.Comparison

public class Comparison
extends Predicate

Comparison represents an inequality expression, comparing two operands. A Comparison is a kind of boolean expression that directly compares its two operands. There are six comparison operations, whose names include: equals, notEquals, lessThan, moreThan, notLessThan, and notMoreThan.

Version:

Broker@Cloud 1.0

Author:

Anthony J H Simons

Field Summary

Fields inherited from class uk.ac.sheffield.vtts.model.Function

expressions, maxOperands

Fields inherited from class uk.ac.sheffield.vtts.model.Expression

factory, type

Fields inherited from class uk.ac.sheffield.vtts.model.Named

name

Constructor Summary

Constructors

Constructor and Description
Comparison() Creates a default Comparison.
Comparison(java.lang.String name) Creates a Comparison with the given name.

Method Summary

Methods

Modifier and Type	Method and Description
protected java.lang.Boolean	equals(java.lang.Object first, java.lang.Object second) Reports whether two values are equal.
java.lang.Boolean	evaluate() Executes this Comparison predicate on its operands.
boolean	isConsistent() Reports whether this Comparison is consistent.
protected java.lang.Boolean	lessThan(java.lang.Object first, java.lang.Object second) Reports whether the first value is less than the second value.
protected java.lang.Boolean	moreThan(java.lang.Object first, java.lang.Object second) Reports whether the first value is greater than the second value.
protected void	nameCheck() Checks the name of a Comparison predicate and sets the expected number of operands.
Predicate	negate() Returns the complement of this Comparison.
protected java.lang.Boolean	notEquals(java.lang.Object first, java.lang.Object second) Reports whether two values are not equal.
protected java.lang.Boolean	notLessThan(java.lang.Object first, java.lang.Object second) Reports whether the first value is greater than, or equal to the second value.
protected java.lang.Boolean	notMoreThan(java.lang.Object first, java.lang.Object second) Reports whether the first value is less than, or equal to the second value.
protected void	rebindFalse() Rebinds the unbound operands of this Comparison, so that it yields false.
protected void	rebindTrue() Rebinds the unbound operands of this Comparison, so that it yields true.
java.util.List<Predicate>	refine() Returns a list of refinements of this Comparison.
Predicate	reverse() Returns the symmetric reversal of this Comparison.
boolean	subsumes(Predicate other) Tests whether this Comparison subsumes the other Predicate.
protected boolean	subsumesComparison(Predicate other) Tests whether this comparison subsumes the other comparison.
protected void	typeCheck() Checks that the operand types are consistent, and the result type is Boolean.

Methods inherited from class uk.ac.sheffield.vtts.model.Predicate

isFalseConstant, normalise, rebind, rebind, setType, subsumesAllDisjunctsOf, subsumesOneConjunctOf, subsumesProposition

Methods inherited from class uk.ac.sheffield.vtts.model.Function

addExpression, assign, equals, getExpressions, getType, hashCode, isAssignable, isBound, operand, resolve, setName, toString, unbind

Methods inherited from class uk.ac.sheffield.vtts.model.Expression

getName, isBottom, isOrdered

Methods inherited from class uk.ac.sheffield.vtts.model.Named

setName

Methods inherited from class uk.ac.sheffield.vtts.model.Element

safeEquals, safeHashCode, semanticError

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Constructor Detail

Comparison

public Comparison()

Creates a default Comparison. The result type is automatically set to "Boolean".

Comparison

public Comparison(java.lang.String name)

Creates a Comparison with the given name. Checks that the name is one of the legal names for a Comparison. The result type is automatically set to "Boolean".

Parameters:

name - the name of this Comparison.

Method Detail

nameCheck

protected void nameCheck()

Checks the name of a Comparison predicate and sets the expected number of operands. All Comparisons expect two operands.

Specified by:

nameCheck in class Function

typeCheck

protected void typeCheck()

Checks that the operand types are consistent, and the result type is Boolean. Caches the operand valueType, which is used as a dispatching token during evaluation.

Specified by:

typeCheck in class Function

subsumes

public boolean subsumes(Predicate other)

Tests whether this Comparison subsumes the other Predicate. If the other Predicate is also a Comparison, tests whether this is a broader Comparison than the other. If the other Predicate is an AND-Proposition, tests whether this Comparison subsumes one of the other's conjuncts. Otherwise, returns false.

Specified by:

subsumes in class Predicate

Parameters:

other - the other Predicate.

Returns:

true if this Comparison subsumes the other Predicate.

subsumesComparison

protected boolean subsumesComparison(Predicate other)

Tests whether this comparison subsumes the other comparison. If the two conditions test the same operands, then if this condition is identical to, or broader than, the other condition, returns true; otherwise returns false.

Parameters:

other - the other comparison.

Returns:

true if this comparison subsumes the other one.

isConsistent

public boolean isConsistent()

Reports whether this Comparison is consistent. Returns false in the two cases of: lessThan(x, bottom) and moreThan(bottom, y). Otherwise returns true.

Overrides:

isConsistent in class Predicate

Returns:

true if this Comparison is consistent.

negate

public Predicate negate()

Returns the complement of this Comparison. Negates the inequality relationship, but keeps the same operands.

Overrides:

negate in class Predicate

Returns:

the complement of this Predicate.

reverse

public Predicate reverse()

Returns the symmetric reversal of this Comparison. Reverses the inequality relationship and reverses the order of operands.

Returns:

a symmetric Comparison expressing the same logical relationship, but with the order of operands reversed.

refine

public java.util.List<Predicate> refine()

Returns a list of refinements of this Comparison. If this Comparison can be broken down into more atomic Comparisons, breaks it down into its atomic Comparisons, returning these as a list. Otherwise, returns this Comparison as a singleton list.

Overrides:

refine in class Predicate

Returns:

the refinements of this Comparison.

evaluate

public java.lang.Boolean evaluate()
                           throws SemanticError

Executes this Comparison predicate on its operands. Checks the consistency of the operand types and then branches according to the name of this Comparison predicate.

Specified by:

evaluate in class Predicate

Returns:

true if the predicate holds between the operands.

Throws:

SemanticError

equals

protected java.lang.Boolean equals(java.lang.Object first,
                       java.lang.Object second)

Reports whether two values are equal. Uses Java's built-in equals() method to judge the equality of two values of the same type.

Parameters:

first - the first value.

second - the second value.

Returns:

true, if the values are equal.

notEquals

protected java.lang.Boolean notEquals(java.lang.Object first,
                          java.lang.Object second)

Reports whether two values are not equal. Returns the logical negation of the comparison: equals(first, second).

Parameters:

first - the first value.

second - the second value.

Returns:

true, if the values are not equal.

lessThan

protected java.lang.Boolean lessThan(java.lang.Object first,
                         java.lang.Object second)

Reports whether the first value is less than the second value. This is determined according to the value-type. String and Character values are compared lexicographically; Number values are compared by magnitude using Java's built-in compareTo(first, second).

Parameters:

first - the first value.

second - the second value.

Returns:

true, if the first value is less than the second value.

moreThan

protected java.lang.Boolean moreThan(java.lang.Object first,
                         java.lang.Object second)

Reports whether the first value is greater than the second value. Returns the result of the reverse comparison: lessThan(second, first).

Parameters:

first - the first value.

second - the second value.

Returns:

true, if the first value is greater than the second value.

notLessThan

protected java.lang.Boolean notLessThan(java.lang.Object first,
                            java.lang.Object second)

Reports whether the first value is greater than, or equal to the second value. Returns the result of the disjunction: equals(first, second) OR lessThan(second, first).

Parameters:

first - the first value.

second - the second value.

Returns:

true, if the first value is not less than the second value.

notMoreThan

protected java.lang.Boolean notMoreThan(java.lang.Object first,
                            java.lang.Object second)

Reports whether the first value is less than, or equal to the second value. Returns the result of the disjunction: equals(first, second) OR lessThan(first, second).

Parameters:

first - the first value.

second - the second value.

Returns:

true, if the first value is not greater than the second value.

rebindTrue

protected void rebindTrue()

Rebinds the unbound operands of this Comparison, so that it yields true. If either operand is unbound, binds it to a value satisfying the constraint with respect to the other operand. If both are unbound, first binds the second operand to a default value.

Specified by:

rebindTrue in class Predicate

rebindFalse

protected void rebindFalse()

Rebinds the unbound operands of this Comparison, so that it yields false. If either operand is unbound, binds it to a value violating the constraint with respect to the other operand. If both are unbound, first binds the second operand to a default value.

Specified by:

rebindFalse in class Predicate