org.apache.commons.collections

Class ClosureUtils


public class ClosureUtils
extends java.lang.Object

ClosureUtils provides reference implementations and utilities for the Closure functor interface. The supplied closures are: All the supplied closures are Serializable.
Version:
$Revision: 1.9 $ $Date: 2004/05/26 21:50:52 $
Author:
Stephen Colebourne
Since:
Commons Collections 3.0

Constructor Summary

ClosureUtils()
This class is not normally instantiated.

Method Summary

static Closure
asClosure(Transformer transformer)
Creates a Closure that calls a Transformer each time it is called.
static Closure
chainedClosure(Collection closures)
Create a new Closure that calls each closure in turn, passing the result into the next closure.
static Closure
chainedClosure(Closure closure1, Closure closure2)
Create a new Closure that calls two Closures, passing the result of the first into the second.
static Closure
chainedClosure(Closure[] closures)
Create a new Closure that calls each closure in turn, passing the result into the next closure.
static Closure
doWhileClosure(Closure closure, Predicate predicate)
Creates a Closure that will call the closure once and then repeatedly until the predicate returns false.
static Closure
exceptionClosure()
Gets a Closure that always throws an exception.
static Closure
forClosure(int count, Closure closure)
Creates a Closure that will call the closure count times.
static Closure
ifClosure(Predicate predicate, Closure trueClosure, Closure falseClosure)
Create a new Closure that calls one of two closures depending on the specified predicate.
static Closure
invokerClosure(String methodName)
Creates a Closure that will invoke a specific method on the closure's input object by reflection.
static Closure
invokerClosure(String methodName, Class[] paramTypes, Object[] args)
Creates a Closure that will invoke a specific method on the closure's input object by reflection.
static Closure
nopClosure()
Gets a Closure that will do nothing.
static Closure
switchClosure(Map predicatesAndClosures)
Create a new Closure that calls one of the closures depending on the predicates.
static Closure
switchClosure(Predicate[] predicates, Closure[] closures)
Create a new Closure that calls one of the closures depending on the predicates.
static Closure
switchClosure(Predicate[] predicates, Closure[] closures, Closure defaultClosure)
Create a new Closure that calls one of the closures depending on the predicates.
static Closure
switchMapClosure(Map objectsAndClosures)
Create a new Closure that uses the input object as a key to find the closure to call.
static Closure
whileClosure(Predicate predicate, Closure closure)
Creates a Closure that will call the closure repeatedly until the predicate returns false.

Constructor Details

ClosureUtils

public ClosureUtils()
This class is not normally instantiated.

Method Details

asClosure

public static Closure asClosure(Transformer transformer)
Creates a Closure that calls a Transformer each time it is called. The transformer will be called using the closure's input object. The transformer's result will be ignored.
Parameters:
transformer - the transformer to run each time in the closure, null means nop
Returns:
the closure

chainedClosure

public static Closure chainedClosure(Collection closures)
Create a new Closure that calls each closure in turn, passing the result into the next closure. The ordering is that of the iterator() method on the collection.
Parameters:
closures - a collection of closures to chain
Returns:
the chained closure

chainedClosure

public static Closure chainedClosure(Closure closure1,
                                     Closure closure2)
Create a new Closure that calls two Closures, passing the result of the first into the second.
Parameters:
closure1 - the first closure
closure2 - the second closure
Returns:
the chained closure

chainedClosure

public static Closure chainedClosure(Closure[] closures)
Create a new Closure that calls each closure in turn, passing the result into the next closure.
Parameters:
closures - an array of closures to chain
Returns:
the chained closure

doWhileClosure

public static Closure doWhileClosure(Closure closure,
                                     Predicate predicate)
Creates a Closure that will call the closure once and then repeatedly until the predicate returns false.
Parameters:
closure - the closure to call repeatedly, not null
predicate - the predicate to use as an end of loop test, not null
Returns:
the do-while closure
See Also:
WhileClosure

exceptionClosure

public static Closure exceptionClosure()
Gets a Closure that always throws an exception. This could be useful during testing as a placeholder.
Returns:
the closure

forClosure

public static Closure forClosure(int count,
                                 Closure closure)
Creates a Closure that will call the closure count times.

A null closure or zero count returns the NOPClosure.

Parameters:
count - the number of times to loop
closure - the closure to call repeatedly
Returns:
the for closure
See Also:
ForClosure

ifClosure

public static Closure ifClosure(Predicate predicate,
                                Closure trueClosure,
                                Closure falseClosure)
Create a new Closure that calls one of two closures depending on the specified predicate.
Parameters:
predicate - the predicate to switch on
trueClosure - the closure called if the predicate is true
falseClosure - the closure called if the predicate is false
Returns:
the switch closure
See Also:
IfClosure

invokerClosure

public static Closure invokerClosure(String methodName)
Creates a Closure that will invoke a specific method on the closure's input object by reflection.
Parameters:
methodName - the name of the method
Returns:
the invoker closure

invokerClosure

public static Closure invokerClosure(String methodName,
                                     Class[] paramTypes,
                                     Object[] args)
Creates a Closure that will invoke a specific method on the closure's input object by reflection.
Parameters:
methodName - the name of the method
paramTypes - the parameter types
args - the arguments
Returns:
the invoker closure

nopClosure

public static Closure nopClosure()
Gets a Closure that will do nothing. This could be useful during testing as a placeholder.
Returns:
the closure
See Also:
NOPClosure

switchClosure

public static Closure switchClosure(Map predicatesAndClosures)
Create a new Closure that calls one of the closures depending on the predicates.

The Map consists of Predicate keys and Closure values. A closure is called if its matching predicate returns true. Each predicate is evaluated until one returns true. If no predicates evaluate to true, the default closure is called. The default closure is set in the map with a null key. The ordering is that of the iterator() method on the entryset collection of the map.

Parameters:
predicatesAndClosures - a map of predicates to closures
Returns:
the switch closure
See Also:
SwitchClosure

switchClosure

public static Closure switchClosure(Predicate[] predicates,
                                    Closure[] closures)
Create a new Closure that calls one of the closures depending on the predicates.

The closure at array location 0 is called if the predicate at array location 0 returned true. Each predicate is evaluated until one returns true.

Parameters:
predicates - an array of predicates to check, not null
closures - an array of closures to call, not null
Returns:
the switch closure
See Also:
SwitchClosure

switchClosure

public static Closure switchClosure(Predicate[] predicates,
                                    Closure[] closures,
                                    Closure defaultClosure)
Create a new Closure that calls one of the closures depending on the predicates.

The closure at array location 0 is called if the predicate at array location 0 returned true. Each predicate is evaluated until one returns true. If no predicates evaluate to true, the default closure is called.

Parameters:
predicates - an array of predicates to check, not null
closures - an array of closures to call, not null
defaultClosure - the default to call if no predicate matches
Returns:
the switch closure
See Also:
SwitchClosure

switchMapClosure

public static Closure switchMapClosure(Map objectsAndClosures)
Create a new Closure that uses the input object as a key to find the closure to call.

The Map consists of object keys and Closure values. A closure is called if the input object equals the key. If there is no match, the default closure is called. The default closure is set in the map using a null key.

Parameters:
objectsAndClosures - a map of objects to closures
Returns:
the closure
See Also:
SwitchClosure

whileClosure

public static Closure whileClosure(Predicate predicate,
                                   Closure closure)
Creates a Closure that will call the closure repeatedly until the predicate returns false.
Parameters:
predicate - the predicate to use as an end of loop test, not null
closure - the closure to call repeatedly, not null
Returns:
the while closure
See Also:
WhileClosure

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