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## Package com.bea.p13n.expression

This package provides interfaces and classes for constructing and executing runtime interpreted expression trees.

See
Description

Interface Summary
Evaluator | An interface that is implemented by the classes that can evaluate an `Expression`.
Executor | The Executor interface is implemented by a class that can perform the Unification-Validation-Evaluation cycle on an Expression.
Expression | An interface implemented by all simple and complex expressions.
ExpressionList | Simple wrapper interface for List for storing sub-components of an expression.
Optimizer | The `Optimizer` interface is implemented by the class that can optimize an `Expression`.
ProxyExpression | An interface implemented by the class that need to act as a proxy to the original expression.
UnificationList | An interface for a class that maps variable names to the variable values.
Unifier | An interface implemented by classes that can unify (replace occurrences of a variable with a value) an expression.
Validator | An interface that is implemented by a class that can validate various types of expressions.

Class Summary
ExpressionFactory | A factory class to create instances of the various implementation classes in the expression package.

Exception Summary
ComparisonException | An Exception class for Comparison related exceptions.
ExpressionException | Base class for all `Exception`s in the expression package.
IntrospectionException | Exception class for Java reflection introspection errors.
InvalidExpressionException | Exception class to signal Expression validation errors.
MethodCallException | Exception class for MethodCall related exceptions.
UnboundVariableException | An Exception class to signal that a variable in an expression has not been unified with a value.

## Package com.bea.p13n.expression Description

This package provides interfaces and classes for constructing and executing runtime interpreted expression trees. Expression trees can contain variables, common operators, Java literals and arbitrary method calls. This package also provides various services such as validation for validating an expression, unification for unifying an expression, and evaluation for evaluating an expression. These service can be constructed and used through the `ExpressionFactory`.

The expression package includes the following classes of operators:

- Logical
- Math
- Collection
- String
- Comparative
- Miscellaneous

Note: There is a special Expression class called `ProxyExpression` that acts as a proxy to an embedded expression.

See Also
  `ExpressionFactory`, `Evaluator`, `Validator`, `Unifier`, `Executor`, `Expression`, `ProxyExpression`

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