freemarker.template.expression
Interface Expression

All Known Subinterfaces:

Binary, Operator, Unary, Variable

All Known Implementing Classes:

AbstractBinary, And, BooleanLiteral, Constant, Divide, Dot, DynamicKeyName, EmptyLiteral, Equals, GreaterThan, GreaterThanOrEquals, HashLiteral, Identifier, LessThan, LessThanOrEquals, ListLiteral, ListRange, MethodCall, Minus, Modulo, Multiply, Not, NotEquals, NumberLiteral, Or, Plus, StringLiteral

public interface Expression

An Expression can return a TemplateModel value. An expression is used whenever we want to interact with the template models. An expression can be simple, such as an identifier, or more complex, such as a dynamic key name or a concatenation operator.

Expressions can be (in fact, usually are) nested. For instance, a comparison of two concatenation operations may be represented as follows:

                         Equals
                           |
          +----------------+---------------+
          |                                |
          |Plus                            | Plus
     +----+----+                     +-----+-----+
     |         |                     |           |
     |         |                     |           |
 identifier identifier           identifier      + dynamic-key-name
                                                 |
                                                 |
                                                 + identifier
 

Each node on the tree represents a different expression object.

Once complete (i.e. parsed), expressions should be considered immutable.

Method Summary

TemplateModel	getAsTemplateModel(TemplateWriteableHashModel modelRoot) The TemplateModel value of this Expression.
int	getType() Determine the type of result that can be calculated by this expression.
boolean	isComplete() Is the Expression complete?
boolean	isConstant() Determine whether result calculated by this expression is a constant value.
Expression	resolveExpression() Resolves the current expression, possibly into a different expression object.

Method Detail

getAsTemplateModel

TemplateModel getAsTemplateModel(TemplateWriteableHashModel modelRoot)
                                 throws TemplateException

The TemplateModel value of this Expression.

Parameters:

modelRoot - the template model that will be evaluated by the expression

Throws:

TemplateException - the expression could not be evaluated for some reason

isComplete

boolean isComplete()

Is the Expression complete?

Returns:

true if this Expression is complete, otherwise false

getType

int getType()

Determine the type of result that can be calculated by this expression. This is in the form of an integer constant ored together from values in the ExpressionUtils class.

isConstant

boolean isConstant()

Determine whether result calculated by this expression is a constant value.

resolveExpression

Expression resolveExpression()
                             throws TemplateException

Resolves the current expression, possibly into a different expression object. This is loosely equivalent to the serialization protocol's readResolve method. Situations where this may be used are:

• Caching frequently-used expression objects
• Evaluating constant expressions, and returning a constant reference

Throws:

TemplateException