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## org.apache.commons.collections
Class ClosureUtils

    java.lang.Object
      |
      +--org.apache.commons.collections.ClosureUtils

public class ClosureUtils
extends Object

`ClosureUtils` provides reference implementations and utilities for the Closure functor interface. The supplied closures are:

- Invoker - invokes a method on the input object
- For - repeatedly calls a closure for a fixed number of times
- While - repeatedly calls a closure while a predicate is true
- DoWhile - repeatedly calls a closure while a predicate is true
- Chained - chains two or more closures together
- Switch - calls one closure based on one or more predicates
- SwitchMap - calls one closure looked up from a Map
- Transformer - wraps a Transformer as a Closure
- NOP - does nothing
- Exception - always throws an exception

All the supplied closures are Serializable.

Since:
  Commons Collections 3.0
Version:
  $Revision: 1.9 $ $Date: 2004/05/26 21:50:52 $
Author:
  Stephen Colebourne

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(Closure[] 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(Collection 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.

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Constructor Detail

### ClosureUtils

    public ClosureUtils()

  This class is not normally instantiated.

Method Detail

### 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
  See Also:
    `ExceptionClosure`

### 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`

### 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
  See Also:
    `TransformerClosure`

### 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`

### 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
  Throws:
    `IllegalArgumentException` - if either argument is null
  See Also:
    `WhileClosure`

### 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
  Throws:
    `IllegalArgumentException` - if either argument is null
  See Also:
    `WhileClosure`

### 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
  Throws:
    `IllegalArgumentException` - if the method name is null
  See Also:
    `InvokerTransformer`, `TransformerClosure`

### 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
  Throws:
    `IllegalArgumentException` - if the method name is null
    `IllegalArgumentException` - if the paramTypes and args don't match
  See Also:
    `InvokerTransformer`, `TransformerClosure`

### 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
  Throws:
    `IllegalArgumentException` - if either closure is null
  See Also:
    `ChainedClosure`

### 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
  Throws:
    `IllegalArgumentException` - if the closures array is null
    `IllegalArgumentException` - if any closure in the array is null
  See Also:
    `ChainedClosure`

### 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
  Throws:
    `IllegalArgumentException` - if the closures collection is null
    `IllegalArgumentException` - if the closures collection is empty
    `IllegalArgumentException` - if any closure in the collection is null
  See Also:
    `ChainedClosure`

### 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
  Throws:
    `IllegalArgumentException` - if the predicate is null
    `IllegalArgumentException` - if either closure is null
  See Also:
    `IfClosure`

### 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
  Throws:
    `IllegalArgumentException` - if the either array is null
    `IllegalArgumentException` - if any element in the arrays is null
    `IllegalArgumentException` - if the arrays are different sizes
  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
  Throws:
    `IllegalArgumentException` - if the either array is null
    `IllegalArgumentException` - if any element in the arrays is null
    `IllegalArgumentException` - if the arrays are different sizes
  See Also:
    `SwitchClosure`

### 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
  Throws:
    `IllegalArgumentException` - if the map is null
    `IllegalArgumentException` - if the map is empty
    `IllegalArgumentException` - if any closure in the map is null
    `ClassCastException` - if the map elements are of the wrong type
  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
  Throws:
    `IllegalArgumentException` - if the map is null
    `IllegalArgumentException` - if the map is empty
    `IllegalArgumentException` - if any closure in the map is null
  See Also:
    `SwitchClosure`

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