uk.ac.sheffield.vtts.model

Class Assignment

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.Assignment

public class Assignment
extends Function

Assignment represents a single variable-binding expression. Assignment is both an initialisation operator and a re-assignment operator. It can be used to populate Input, Output and Variable parameters with their initial value; and it can also be used to re-assign a new value to a Variable. The Assignment operator name indicates whether the assigned value should be exactly equal to a given value, more or less than a given value, or not equal to a given value. The valid operator names include: equals, notEquals, moreThan, lessThan. The latter two operators may also be used with a single operand for unit increment or decrement operations.

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
Assignment() Creates a default Assignment.
Assignment(java.lang.String name) Creates a named Assignment.
Assignment(java.lang.String name, java.lang.String type) Creates a named and typed Assignment.

Method Summary

Methods

Modifier and Type	Method and Description
Assignment	addExpression(Expression expression) Adds an expression as an operand to this Assignment expression.
java.lang.Object	evaluate() Executes this Assignment on its operands.
protected void	nameCheck() Checks the operator name of this Assignment expression and sets the maximum number of operands to two.
void	rebind() Rebinds the unbound operands of this Assignment.
void	rebind(java.lang.Object result) Rebinds the unbound operands of this Assignment, so that it yields the given (null) result.
Assignment	setType(java.lang.String type) Sets the type of this Assignment.
protected void	typeCheck() Checks that the operand types of this Assignment are consistent, and the result type is Void.

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

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

Assignment

public Assignment()

Creates a default Assignment. Sets the type to "Void".

Assignment

public Assignment(java.lang.String name)

Creates a named Assignment. The operator name indicates what kind of assignment is intended, from: "equals, notEquals, moreThan, lessThan". Also sets the type to "Void".

Parameters:

name - the operator name.

Assignment

public Assignment(java.lang.String name,
          java.lang.String type)

Creates a named and typed Assignment. The operator name indicates the kind of assignment, from: "equals, notEquals, moreThan, lessThan". Always sets the type to "Void", no matter what type was supplied (fail-safe).

Parameters:

name - the assignment operator name.

type - the type of the assignment, "Void".

Method Detail

nameCheck

protected void nameCheck()

Checks the operator name of this Assignment expression and sets the maximum number of operands to two. The legal operator names include "equals, notEquals, moreThan, lessThan". The latter two may be used for unit increment and decrement with a single variable operand; the ModelFactory has a notion of what it means to increment or decrement a value of each model type.

Specified by:

nameCheck in class Function

typeCheck

protected void typeCheck()
                  throws SemanticError

Checks that the operand types of this Assignment are consistent, and the result type is Void. If this Assignment has one operand, then this could be any single type for an increment or decrement; otherwise both operands must be of the same type.

Specified by:

typeCheck in class Function

Throws:

SemanticError - if a type inconsistency is detected.

setType

public Assignment setType(java.lang.String type)

Sets the type of this Assignment. Always sets the type to "Void", no matter what type was supplied (fail-safe).

Overrides:

setType in class Expression

Parameters:

type - the type to set.

Returns:

this Parameter.

addExpression

public Assignment addExpression(Expression expression)

Adds an expression as an operand to this Assignment expression.

Overrides:

addExpression in class Function

Parameters:

expression - the operand expression.

Returns:

this functional expression.

evaluate

public java.lang.Object evaluate()

Executes this Assignment on its operands. Expects the first operand to be an assignable Parameter. Performs one of an assignment, a unit increment, or unit decrement operation. The notEquals operator is treated as a unit increment.

Specified by:

evaluate in class Expression

Returns:

the Java object denoting the value of this Expression.

rebind

public void rebind()

Rebinds the unbound operands of this Assignment. Degenerate version of this method, which does nothing.

Overrides:

rebind in class Function

rebind

public void rebind(java.lang.Object result)

Rebinds the unbound operands of this Assignment, so that it yields the given (null) result. Degenerate version of this method, which does nothing.

Specified by:

rebind in class Expression

Parameters:

result - the desired bound value.