dk.rode.thesis.interpreter
Class TypedExpressionDecorator<E>

java.lang.Object
  dk.rode.thesis.interpreter.TypedExpressionDecorator<E>

Type Parameters:

E - The type of value the evaluation of the decorated expression produces.

All Implemented Interfaces:

Expression<E>, InitialisableExpression<E>, TypedExpression<E>, Copyable<Expression<E>>, StrictCopyable<Expression<E>>

public class TypedExpressionDecorator<E>
extends Object
implements TypedExpression<E>, InitialisableExpression<E>

A type expression decorator allows any expression to be explicitly associated with the type of the values the evaluation of it will produce.

In case the decorated expression is initialisable, it will be initialised by the initialise() method defined in this decorator. If the decorated expression is not initialisable, the initialise() and isInitialised() methods does nothing.

Implementation notes:
This is a fine example of the Decorator pattern at work.

Author:

Gunni Rode / rode.dk

Nested Class Summary

Nested classes/interfaces inherited from interface dk.rode.thesis.interpreter.Expression

Expression.SymbolIdiom

Field Summary

protected Expression<E>	expression The decorated expression.
protected boolean	includeTypeInfo True if the evaluation type of expression will be included in the symbolic representation of it, false if not.
protected Class<E>	type The type of values the evaluation of expression produces.

Constructor Summary

TypedExpressionDecorator(Expression<E> expression, Class<E> type)
Constructor, which decorates the expression supplied as expression having the type supplied as type.

TypedExpressionDecorator(Expression<E> expression, Class<E> type, boolean includeTypeInfo)
Constructor, which decorates the expression supplied as expression having the type supplied as type.

TypedExpressionDecorator(TypedExpression<E> expression)
Constructor, which decorates the typed expression supplied as expression.

TypedExpressionDecorator(TypedExpressionDecorator<E> expression)
Copy constructor.

Method Summary

String	asSymbol(Context context) Returns x, where x is the symbolic representation of the decorated expression, or if type information is included, Type{x}, where Type is the simple name of the type.
boolean	contains(Expression<?> expression) Returns true if this expression is or contains the expression supplied as expression, false if not.
TypedExpressionDecorator<E>	copy() Copies this typed expression.
boolean	equals(Object object) Returns true if object is a typed expression decorator decorating the same expressions as this decorator, tested using equals(Object), false if not.
E	evaluate(Context context) Evaluates this expression and returns the result.
int	hashCode() Returns the hash code of this expression.
TypedExpressionDecorator<E>	initialise() Initialises this expression before evaluation.
boolean	isInitialised() Returns true if this expression has been initialised, and hence ready to be evaluated, false if not.
String	name() The stand-alone symbol name for this expression.
List<Expression<?>>	operands() Returns the expression operands used by this expression, in order.
String	toString() Returns the string representation of this expression.
Class<E>	type() Return the type of value the evaluation of this expression produces.

Methods inherited from class java.lang.Object

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

Field Detail

expression

protected final Expression<E> expression

The decorated expression.

Never null.

includeTypeInfo

protected final boolean includeTypeInfo

True if the evaluation type of expression will be included in the symbolic representation of it, false if not.

Default false.

type

protected final Class<E> type

The type of values the evaluation of expression produces.

Never null.

Constructor Detail

TypedExpressionDecorator

public TypedExpressionDecorator(Expression<E> expression,
                                Class<E> type)

Constructor, which decorates the expression supplied as expression having the type supplied as type.

The symbolic representation of expression will include type information regarding type.

Parameters:

expression - The expression to decorate; cannot be null.

type - The actual type; cannot be null.

Throws:

NullPointerException - If either argument is null.

TypedExpressionDecorator

public TypedExpressionDecorator(Expression<E> expression,
                                Class<E> type,
                                boolean includeTypeInfo)

Constructor, which decorates the expression supplied as expression having the type supplied as type.

The symbolic representation of expression will include type information regarding type if includeTypeInfo is true, not if false.

Parameters:

expression - The expression to decorate; cannot be null.

type - The type of values the evaluation of expression produces.

includeTypeInfo - True to include type information in the symbolic representation of expression, false if not.

Throws:

NullPointerException - If expression or type is null.

TypedExpressionDecorator

public TypedExpressionDecorator(TypedExpression<E> expression)

Constructor, which decorates the typed expression supplied as expression.

The symbolic representation of expression will include type information regarding the type of expression.

Parameters:

expression - The typed expression to decorate; cannot be null.

Throws:

NullPointerException - If expression is null.

TypedExpressionDecorator

public TypedExpressionDecorator(TypedExpressionDecorator<E> expression)

Copy constructor.

Parameters:

expression - The expression to copy; cannot be null.

Throws:

NullPointerException - If expression is null.

Method Detail

asSymbol

public String asSymbol(Context context)
                throws ExpressionException

Returns x, where x is the symbolic representation of the decorated expression, or if type information is included, Type{x}, where Type is the simple name of the type.

Specified by:

asSymbol in interface Expression<E>

Parameters:

context - The context to use; never null.

Returns:

The symbolic representation; never null.

Throws:

ExpressionException - If the symbol cannot be generated.

See Also:

Expression.contains(Expression)

contains

public boolean contains(Expression<?> expression)

Description copied from interface: Expression

Returns true if this expression is or contains the expression supplied as expression, false if not.

The test is performed using identity (==).

Unlike Expression.asSymbol(Context), querying for containment cannot handle cyclic expression references!

Specified by:

contains in interface Expression<E>

Parameters:

expression - The expression to test; cannot be null.

Returns:

True if expression is this expression or contained within this expression, false if not.

See Also:

Expression.asSymbol(Context), Context.touch(Expression)

copy

public TypedExpressionDecorator<E> copy()

Description copied from interface: TypedExpression

Copies this typed expression.

Unlike Expression.asSymbol(Context), copying cannot handle cyclic expression references!

Specified by:

copy in interface Expression<E>

Specified by:

copy in interface InitialisableExpression<E>

Specified by:

copy in interface TypedExpression<E>

Specified by:

copy in interface Copyable<Expression<E>>

Returns:

A copy of this typed expression; never null.

equals

public boolean equals(Object object)

Returns true if object is a typed expression decorator decorating the same expressions as this decorator, tested using equals(Object), false if not.

Overrides:

equals in class Object

Parameters:

object - The object to test; can be null.

Returns:

True if equal, false if not.

evaluate

public E evaluate(Context context)
           throws ExpressionException

Description copied from interface: Expression

Evaluates this expression and returns the result.

There is no guarantee that the evaluation of this expression will terminate!

Specified by:

evaluate in interface Expression<E>

Parameters:

context - The context to use; cannot be null.

Returns:

The result of the evaluation; never null.

Throws:

ExpressionException - If the evaluation fails.

hashCode

public int hashCode()

Returns the hash code of this expression.

Overrides:

hashCode in class Object

Returns:

The hash code.

initialise

public TypedExpressionDecorator<E> initialise()
                                       throws ExpressionException

Description copied from interface: InitialisableExpression

Initialises this expression before evaluation.

Contained initialisable expressions are not initialised!

Specified by:

initialise in interface InitialisableExpression<E>

Returns:

This expression; never null.

Throws:

ExpressionException - If this expression has already been initialised.

isInitialised

public boolean isInitialised()

Description copied from interface: InitialisableExpression

Returns true if this expression has been initialised, and hence ready to be evaluated, false if not.

If this expression has not been initialised when evaluated, the evaluation will throw an exception.

Specified by:

isInitialised in interface InitialisableExpression<E>

Returns:

True if initialised, false if not.

name

public String name()

Description copied from interface: Expression

The stand-alone symbol name for this expression.

Specified by:

name in interface Expression<E>

Returns:

The symbol name; never null.

operands

public List<Expression<?>> operands()

Description copied from interface: Expression

Returns the expression operands used by this expression, in order.

Modifying the returned list will not affect this expression.

Specified by:

operands in interface Expression<E>

Returns:

The operands; never null, but can be empty.

toString

public String toString()

Description copied from interface: Expression

Returns the string representation of this expression.

Unlike Expression.asSymbol(Context), the string generation cannot handle cyclic expression references!

Specified by:

toString in interface Expression<E>

Overrides:

toString in class Object

Returns:

The string representation; never null.

type

public Class<E> type()

Description copied from interface: TypedExpression

Return the type of value the evaluation of this expression produces.

Specified by:

type in interface TypedExpression<E>

Returns:

The type. The only expression type allowed to return null is BreakExpression!