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## org.apache.commons.lang3.reflect
Class ConstructorUtils

    java.lang.Object
      org.apache.commons.lang3.reflect.ConstructorUtils

    public class ConstructorUtils

extends Object

Utility reflection methods focussed on constructors, modelled after `MethodUtils`.

### Known Limitations

#### Accessing Public Constructors In A Default Access Superclass

There is an issue when invoking public constructors contained in a default access superclass. Reflection locates these constructors fine and correctly assigns them as public. However, an `IllegalAccessException` is thrown if the constructors is invoked.

`ConstructorUtils` contains a workaround for this situation. It will attempt to call `setAccessible` on this constructor. If this call succeeds, then the method can be invoked as normal. This call will only succeed when the application has sufficient security privilages. If this call fails then a warning will be logged and the method may fail.

Since:
  2.5
Version:
  $Id: ConstructorUtils.java 925970 2010-03-22 06:22:28Z bayard $
Author:
  Apache Software Foundation, Craig R. McClanahan, Ralph Schaer, Chris Audley, Rey Francois, Gregor Rayman, Jan Sorensen, Robert Burrell Donkin, Rodney Waldhoff

Constructor Summary
`ConstructorUtils()` ConstructorUtils instances should NOT be constructed in standard programming.

Method Summary
`static
`<T> Constructor<T>`
` | `getAccessibleConstructor(Class<T> cls, Class<?>... parameterTypes)` Returns a constructor given a class and signature.
`static
`<T> Constructor<T>`
` | `getAccessibleConstructor(Constructor<T> ctor)` Returns accessible version of the given constructor.
`static
`<T> Constructor<T>`
` | `getMatchingAccessibleConstructor(Class<T> cls, Class<?>... parameterTypes)` Find an accessible constructor with compatible parameters.
`static
`<T> T`
` | `invokeConstructor(Class<T> cls, Object... args)` Returns new instance of `klazz` created using the actual arguments `args`.
`static
`<T> T`
` | `invokeConstructor(Class<T> cls, Object[] args, Class<?>[] parameterTypes)` Returns new instance of `klazz` created using constructor with signature `parameterTypes` and actual arguments `args`.
`static
`<T> T`
` | `invokeExactConstructor(Class<T> cls, Object... args)` Returns new instance of `klazz` created using the actual arguments `args`.
`static
`<T> T`
` | `invokeExactConstructor(Class<T> cls, Object[] args, Class<?>[] parameterTypes)` Returns new instance of `klazz` created using constructor with signature `parameterTypes` and actual arguments `args`.

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

Constructor Detail

### ConstructorUtils

    public ConstructorUtils()

  ConstructorUtils instances should NOT be constructed in standard programming. Instead, the class should be used as `ConstructorUtils.invokeConstructor(cls, args)`.

  This constructor is public to permit tools that require a JavaBean instance to operate.

Method Detail

### invokeConstructor

    public static <T> T invokeConstructor(Class<T> cls,
                                          Object... args)
                               throws NoSuchMethodException,
                                      IllegalAccessException,
                                      InvocationTargetException,
                                      InstantiationException

  Returns new instance of `klazz` created using the actual arguments `args`. The formal parameter types are inferred from the actual values of `args`. See `invokeExactConstructor(Class, Object[], Class[])` for more details.

  The signatures should be assignment compatible.

  Parameters:
    `cls` - the class to be constructed.
    `args` - actual argument array
  Returns:
    new instance of `klazz`
  Throws:
    `NoSuchMethodException` - If the constructor cannot be found
    `IllegalAccessException` - If an error occurs accessing the constructor
    `InvocationTargetException` - If an error occurs invoking the constructor
    `InstantiationException` - If an error occurs instantiating the class
  See Also:
    `invokeConstructor(java.lang.Class, java.lang.Object[], java.lang.Class[])`

### invokeConstructor

    public static <T> T invokeConstructor(Class<T> cls,
                                          Object[] args,
                                          Class<?>[] parameterTypes)
                               throws NoSuchMethodException,
                                      IllegalAccessException,
                                      InvocationTargetException,
                                      InstantiationException

  Returns new instance of `klazz` created using constructor with signature `parameterTypes` and actual arguments `args`.

  The signatures should be assignment compatible.

  Parameters:
    `cls` - the class to be constructed.
    `args` - actual argument array
    `parameterTypes` - parameter types array
  Returns:
    new instance of `klazz`
  Throws:
    `NoSuchMethodException` - if matching constructor cannot be found
    `IllegalAccessException` - thrown on the constructor's invocation
    `InvocationTargetException` - thrown on the constructor's invocation
    `InstantiationException` - thrown on the constructor's invocation
  See Also:
    `Constructor.newInstance(java.lang.Object...)`

### invokeExactConstructor

    public static <T> T invokeExactConstructor(Class<T> cls,
                                               Object... args)
                                    throws NoSuchMethodException,
                                           IllegalAccessException,
                                           InvocationTargetException,
                                           InstantiationException

  Returns new instance of `klazz` created using the actual arguments `args`. The formal parameter types are inferred from the actual values of `args`. See `invokeExactConstructor(Class, Object[], Class[])` for more details.

  The signatures should match exactly.

  Parameters:
    `cls` - the class to be constructed.
    `args` - actual argument array
  Returns:
    new instance of `klazz`
  Throws:
    `NoSuchMethodException` - If the constructor cannot be found
    `IllegalAccessException` - If an error occurs accessing the constructor
    `InvocationTargetException` - If an error occurs invoking the constructor
    `InstantiationException` - If an error occurs instantiating the class
  See Also:
    `invokeExactConstructor(java.lang.Class, java.lang.Object[], java.lang.Class[])`

### invokeExactConstructor

    public static <T> T invokeExactConstructor(Class<T> cls,
                                               Object[] args,
                                               Class<?>[] parameterTypes)
                                    throws NoSuchMethodException,
                                           IllegalAccessException,
                                           InvocationTargetException,
                                           InstantiationException

  Returns new instance of `klazz` created using constructor with signature `parameterTypes` and actual arguments `args`.

  The signatures should match exactly.

  Parameters:
    `cls` - the class to be constructed.
    `args` - actual argument array
    `parameterTypes` - parameter types array
  Returns:
    new instance of `klazz`
  Throws:
    `NoSuchMethodException` - if matching constructor cannot be found
    `IllegalAccessException` - thrown on the constructor's invocation
    `InvocationTargetException` - thrown on the constructor's invocation
    `InstantiationException` - thrown on the constructor's invocation
  See Also:
    `Constructor.newInstance(java.lang.Object...)`

### getAccessibleConstructor

    public static <T> Constructor<T> getAccessibleConstructor(Class<T> cls,
                                                              Class<?>... parameterTypes)

  Returns a constructor given a class and signature.

  Parameters:
    `cls` - the class to be constructed
    `parameterTypes` - the parameter array
  Returns:
    null if matching accessible constructor can not be found
  See Also:
    `Class.getConstructor(java.lang.Class...)`, `getAccessibleConstructor(java.lang.reflect.Constructor)`

### getAccessibleConstructor

    public static <T> Constructor<T> getAccessibleConstructor(Constructor<T> ctor)

  Returns accessible version of the given constructor.

  Parameters:
    `ctor` - prototype constructor object.
  Returns:
    `null` if accessible constructor can not be found.
  See Also:
    `SecurityManager`

### getMatchingAccessibleConstructor

    public static <T> Constructor<T> getMatchingAccessibleConstructor(Class<T> cls,
                                                                      Class<?>... parameterTypes)

  Find an accessible constructor with compatible parameters. Compatible parameters mean that every method parameter is assignable from the given parameters. In other words, it finds constructor that will take the parameters given.

  First it checks if there is constructor matching the exact signature. If no such, all the constructors of the class are tested if their signatures are assignment compatible with the parameter types. The first matching constructor is returned.

  Parameters:
    `cls` - find constructor for this class
    `parameterTypes` - find method with compatible parameters
  Returns:
    a valid Constructor object. If there's no matching constructor, returns `null`.

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