prefuse.data.expression
Interface Expression

All Known Subinterfaces:

Function, Predicate

All Known Implementing Classes:

AbstractExpression, AbstractPredicate, AndPredicate, ArithmeticExpression, BinaryExpression, BooleanLiteral, ColumnExpression, ComparisonPredicate, CompositePredicate, FunctionExpression, GroupExpression, GroupSizeFunction, HoverPredicate, IfExpression, InGroupPredicate, Literal, NotPredicate, NumericLiteral, ObjectLiteral, OrPredicate, QueryExpression, RangePredicate, SearchPredicate, StartVisiblePredicate, ValidatedPredicate, ValidEdgePredicate, VisiblePredicate, XorPredicate

public interface Expression

An Expression is an arbitrary function that takes a single Tuple as an argument. Expressions support both Object-valued and primitive-valued (int, long, float, double, boolean) evaluation methods. The appropriate method to call depends on the particular Expression implementation. A getType(Schema) method provides mechanism for determining the return type of a given Expression instance. A Predicate is an Expression which is guaranteed to support the getBoolean(Tuple) method, is often used to filter tuples.

Expressions also support a listener interface, allowing clients to monitor changes to expressions, namely rearrangements or modification of contained sub-expressions. The Expression interface also supports visitors, which can be used to visit every sub-expression in an expression tree.

Using the various Expression implementations in the Expression package, clients can programatically construct a tree of expressions for use as complex query predicates or as functions for computing a derived data column (see Table.addColumn(String, Expression). Often it is more convenient to write expressions in the prefuse expression language, a SQL-like data manipulation language, and compile the Expression tree using the ExpressionParser. The documentation for the ExpressionParser class includes a full reference for the textual expression language.

Author:

jeffrey heer

Method Summary

void	addExpressionListener(ExpressionListener lstnr) Add a listener to this Expression.
java.lang.Object	get(Tuple t) Evaluate the Expression on the given input Tuple.
boolean	getBoolean(Tuple t) Evaluate the Expression on the given input Tuple.
double	getDouble(Tuple t) Evaluate the Expression on the given input Tuple.
float	getFloat(Tuple t) Evaluate the Expression on the given input Tuple.
int	getInt(Tuple t) Evaluate the Expression on the given input Tuple.
long	getLong(Tuple t) Evaluate the Expression on the given input Tuple.
java.lang.Class	getType(Schema s) Returns the type that this expression evaluates to when tuples with the given Schema are provided as input.
void	removeExpressionListener(ExpressionListener lstnr) Remove a listener to this Expression.
void	visit(ExpressionVisitor v) Passes the visitor through this expression and any sub expressions

Method Detail

getType

java.lang.Class getType(Schema s)

Returns the type that this expression evaluates to when tuples with the given Schema are provided as input.

visit

void visit(ExpressionVisitor v)

Passes the visitor through this expression and any sub expressions

Parameters:

v - the ExpressionVisitor

get

java.lang.Object get(Tuple t)

Evaluate the Expression on the given input Tuple.

Parameters:

t - the input Tuple

Returns:

the Expression return value, as an Object

getInt

int getInt(Tuple t)

Evaluate the Expression on the given input Tuple.

Parameters:

t - the input Tuple

Returns:

the Expression return value, as an int

getLong

long getLong(Tuple t)

Evaluate the Expression on the given input Tuple.

Parameters:

t - the input Tuple

Returns:

the Expression return value, as a long

getFloat

float getFloat(Tuple t)

Evaluate the Expression on the given input Tuple.

Parameters:

t - the input Tuple

Returns:

the Expression return value, as a float

getDouble

double getDouble(Tuple t)

Evaluate the Expression on the given input Tuple.

Parameters:

t - the input Tuple

Returns:

the Expression return value, as a double

getBoolean

boolean getBoolean(Tuple t)

Evaluate the Expression on the given input Tuple.

Parameters:

t - the input Tuple

Returns:

the Expression return value, as a boolean

addExpressionListener

void addExpressionListener(ExpressionListener lstnr)

Add a listener to this Expression.

Parameters:

lstnr - the expression listener to add

removeExpressionListener

void removeExpressionListener(ExpressionListener lstnr)

Remove a listener to this Expression.

Parameters:

lstnr - the expression listener to remove