# 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 safe are Serializable. Factories considered to be unsafe for serialization are:

- Prototype
- Instantiate

Since:
  3.0

- ## Method Summary

  Modifier and Type
  Method
  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 Details

  - ### 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`

  - ### 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`

  - ### 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`

  - ### 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`

  - ### 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`