Evaluating Software Design Patterns
— the "Gang of Four" patterns implemented in Java 6

dk.rode.thesis.interpreter
Class EqualExpression

java.lang.Object
  extended by dk.rode.thesis.interpreter.AbstractExpression<E>
      extended by dk.rode.thesis.interpreter.BinaryExpression<Object,Boolean>
          extended by dk.rode.thesis.interpreter.EqualExpression
All Implemented Interfaces:
Expression<Boolean>, NonTerminalExpression<Boolean>, Copyable<Expression<Boolean>>, StrictCopyable<Expression<Boolean>>

@Participant(value="NonTerminalExpression")
public class EqualExpression
extends BinaryExpression<Object,Boolean>
implements NonTerminalExpression<Boolean>

An equal expression can determine if the result of evaluating two expressions is equal or not, regardless of types.

Author:
Gunni Rode / rode.dk
See Also:
CompareExpression, NotExpression, AndExpression, OrExpression

Nested Class Summary
 
Nested classes/interfaces inherited from interface dk.rode.thesis.interpreter.Expression
Expression.SymbolIdiom
 
Field Summary
 
Fields inherited from class dk.rode.thesis.interpreter.BinaryExpression
first, second
 
Constructor Summary
EqualExpression(EqualExpression expression)
          Copy constructor.
EqualExpression(Expression<?> first, Expression<?> second)
          Constructor.
 
Method Summary
 String asSymbol(Context context)
          Returns x == y, where x is the symbolic representation of the first expression operand and y of the the second.
 EqualExpression copy()
          Copies this expression.
 Boolean evaluate(Context context)
          Evaluates this expression and returns the result.
 String name()
          The stand-alone symbol name for this expression.
 
Methods inherited from class dk.rode.thesis.interpreter.BinaryExpression
asSymbol, asSymbol, operands, toString
 
Methods inherited from class dk.rode.thesis.interpreter.AbstractExpression
contains, equals, hashCode
 
Methods inherited from class java.lang.Object
clone, finalize, getClass, notify, notifyAll, wait, wait, wait
 
Methods inherited from interface dk.rode.thesis.interpreter.Expression
contains, operands, toString
 

Constructor Detail

EqualExpression

public EqualExpression(EqualExpression expression)
Copy constructor.

Parameters:
expression - The expression to copy; cannot be null.
Throws:
NullPointerException - If expression is null.

EqualExpression

public EqualExpression(Expression<?> first,
                       Expression<?> second)
Constructor.

Parameters:
first - The first expression operand; cannot be null.
second - The second expression operand; cannot be null.
Throws:
NullPointerException - If either expression is null.
Method Detail

asSymbol

public String asSymbol(Context context)
                throws ExpressionException
Returns x == y, where x is the symbolic representation of the first expression operand and y of the the second.

Specified by:
asSymbol in interface Expression<Boolean>
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)

copy

public EqualExpression copy()
Description copied from interface: Expression
Copies this expression.

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

Specified by:
copy in interface Expression<Boolean>
Specified by:
copy in interface Copyable<Expression<Boolean>>
Returns:
A copy of this expression; never null.

evaluate

public Boolean 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<Boolean>
Parameters:
context - The context to use; cannot be null.
Returns:
The result of the evaluation; never null.
Throws:
ExpressionException - If the evaluation fails.

name

public final String name()
Description copied from interface: Expression
The stand-alone symbol name for this expression.

Specified by:
name in interface Expression<Boolean>
Returns:
equal

Gunni Rode / rode.dk

Feel free to use and/or modify the Java 6 source code developed for this thesis AT YOUR OWN RISK, but note that the source code comes WITHOUT ANY — and I do mean WITHOUT ANY — form of warranty WHAT SO EVER!

The original thesis and source code are available at rode.dk/thesis.