org.apache.commons.collections4

## Class FactoryUtils

- java.lang.Object
- - org.apache.commons.collections4.FactoryUtils

-     public class FactoryUtils
      extends Object

  `FactoryUtils` provides reference implementations and utilities for the Factory functor interface. The supplied factories are:
  - Prototype - clones a specified object
  - Instantiate - creates objects using reflection
  - Constant - always returns the same object
  - Null - always returns null
  - Exception - always throws an exception

  Since v4.1 only factories which are considered to be unsafe are Serializable. Factories considered to be unsafe for serialization are:

  - Prototype
  - Instantiate
  Since:
    3.0
  Version:
    $Id: FactoryUtils.java 1714362 2015-11-14 20:38:02Z tn $

- - ### Method Summary

    Methods
    Modifier and Type | Method and Description
    --- | ---
    `static <T> Factory<T>` | `constantFactory(T constantToReturn)` Creates a Factory that will return the same object each time the factory is used.
    `static <T> Factory<T>` | `exceptionFactory()` Gets a Factory that always throws an exception.
    `static <T> Factory<T>` | `instantiateFactory(Class<T> classToInstantiate)` Creates a Factory that can create objects of a specific type using a no-args constructor.
    `static <T> Factory<T>` | `instantiateFactory(Class<T> classToInstantiate, Class<?>[] paramTypes, Object[] args)` Creates a Factory that can create objects of a specific type using the arguments specified to this method.
    `static <T> Factory<T>` | `nullFactory()` Gets a Factory that will return null each time the factory is used.
    `static <T> Factory<T>` | `prototypeFactory(T prototype)` Creates a Factory that will return a clone of the same prototype object each time the factory is used.

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

- - ### Method Detail

    - #### exceptionFactory

          public static <T> Factory<T> exceptionFactory()

      Gets a Factory that always throws an exception. This could be useful during testing as a placeholder.
      Type Parameters:
        `T` - the type that the factory creates
      Returns:
        the factory
      See Also:
        `ExceptionFactory`

    - #### nullFactory

          public static <T> Factory<T> nullFactory()

      Gets a Factory that will return null each time the factory is used. This could be useful during testing as a placeholder.
      Type Parameters:
        `T` - the "type" of null object the factory should return.
      Returns:
        the factory
      See Also:
        `ConstantFactory`

    - #### constantFactory

          public static <T> Factory<T> constantFactory(T constantToReturn)

      Creates a Factory that will return the same object each time the factory is used. No check is made that the object is immutable. In general, only immutable objects should use the constant factory. Mutable objects should use the prototype factory.
      Type Parameters:
        `T` - the type that the factory creates
      Parameters:
        `constantToReturn` - the constant object to return each time in the factory
      Returns:
        the `constant` factory.
      See Also:
        `ConstantFactory`

    - #### prototypeFactory

          public static <T> Factory<T> prototypeFactory(T prototype)

      Creates a Factory that will return a clone of the same prototype object each time the factory is used. The prototype will be cloned using one of these techniques (in order):
      - public clone method
      - public copy constructor
      - serialization clone
      Type Parameters:
        `T` - the type that the factory creates
      Parameters:
        `prototype` - the object to clone each time in the factory
      Returns:
        the `prototype` factory, or a `ConstantFactory.NULL_INSTANCE` if the `prototype` is `null`
      Throws:
        `IllegalArgumentException` - if the prototype cannot be cloned
      See Also:
        `PrototypeFactory`

    - #### instantiateFactory

          public static <T> Factory<T> instantiateFactory(Class<T> classToInstantiate)

      Creates a Factory that can create objects of a specific type using a no-args constructor.
      Type Parameters:
        `T` - the type that the factory creates
      Parameters:
        `classToInstantiate` - the Class to instantiate each time in the factory
      Returns:
        the `reflection` factory
      Throws:
        `NullPointerException` - if the classToInstantiate is null
      See Also:
        `InstantiateFactory`

    - #### instantiateFactory

          public static <T> Factory<T> instantiateFactory(Class<T> classToInstantiate,
                                          Class<?>[] paramTypes,
                                          Object[] args)

      Creates a Factory that can create objects of a specific type using the arguments specified to this method.
      Type Parameters:
        `T` - the type that the factory creates
      Parameters:
        `classToInstantiate` - the Class to instantiate each time in the factory
        `paramTypes` - parameter types for the constructor, can be null
        `args` - the arguments to pass to the constructor, can be null
      Returns:
        the `reflection` factory
      Throws:
        `NullPointerException` - if the classToInstantiate is null
        `IllegalArgumentException` - if the paramTypes and args don't match
        `IllegalArgumentException` - if the constructor doesn't exist
      See Also:
        `InstantiateFactory`

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