# Class AlgorithmParameterGenerator

java.lang.Object
java.security.AlgorithmParameterGenerator

public class AlgorithmParameterGenerator extends Object
The `AlgorithmParameterGenerator` class is used to generate a set of parameters to be used with a certain algorithm. Parameter generators are constructed using the `getInstance` factory methods (static methods that return instances of a given class).

The object that will generate the parameters can be initialized in two different ways: in an algorithm-independent manner, or in an algorithm-specific manner:

- The algorithm-independent approach uses the fact that all parameter generators share the concept of a "size" and a source of randomness. The measure of size is universally shared by all algorithm parameters, though it is interpreted differently for different algorithms. For example, in the case of parameters for the DSA algorithm, "size" corresponds to the size of the prime modulus (in bits). When using this approach, algorithm-specific parameter generation values - if any - default to some standard values, unless they can be derived from the specified size.
- The other approach initializes a parameter generator object using algorithm-specific semantics, which are represented by a set of algorithm-specific parameter generation values. To generate Diffie-Hellman system parameters, for example, the parameter generation values usually consist of the size of the prime modulus and the size of the random exponent, both specified in number of bits.

In case the client does not explicitly initialize the `AlgorithmParameterGenerator` (via a call to an `init` method), each provider must supply (and document) a default initialization. See the Keysize Restriction sections of the JDK Providers document for information on the AlgorithmParameterGenerator defaults used by JDK providers. However, note that defaults may vary across different providers. Additionally, the default value for a provider may change in a future version. Therefore, it is recommended to explicitly initialize the `AlgorithmParameterGenerator` instead of relying on provider-specific defaults.

Every implementation of the Java platform is required to support the following standard `AlgorithmParameterGenerator` algorithms and keysizes in parentheses:

- `DiffieHellman` (1024, 2048)
- `DSA` (1024, 2048)

These algorithms are described in the AlgorithmParameterGenerator section of the Java Security Standard Algorithm Names Specification. Consult the release documentation for your implementation to see if any other algorithms are supported.

Since:
  1.2
External Specifications
  - Java Security Standard Algorithm Names
See Also:
  - `AlgorithmParameters`
  - `AlgorithmParameterSpec`

- ## Constructor Summary

  Constructors
  Modifier
  Constructor
  Description
  `protected`
  `AlgorithmParameterGenerator(AlgorithmParameterGeneratorSpi paramGenSpi, Provider provider, String algorithm)`
  Creates an `AlgorithmParameterGenerator` object.

- ## Method Summary

  Modifier and Type
  Method
  Description
  `final AlgorithmParameters`
  `generateParameters()`
  Generates the parameters.
  `final String`
  `getAlgorithm()`
  Returns the standard name of the algorithm this parameter generator is associated with.
  `static AlgorithmParameterGenerator`
  `getInstance(String algorithm)`
  Returns an `AlgorithmParameterGenerator` object for generating a set of parameters to be used with the specified algorithm.
  `static AlgorithmParameterGenerator`
  `getInstance(String algorithm, String provider)`
  Returns an `AlgorithmParameterGenerator` object for generating a set of parameters to be used with the specified algorithm.
  `static AlgorithmParameterGenerator`
  `getInstance(String algorithm, Provider provider)`
  Returns an `AlgorithmParameterGenerator` object for generating a set of parameters to be used with the specified algorithm.
  `final Provider`
  `getProvider()`
  Returns the provider of this algorithm parameter generator object.
  `final void`
  `init(int size)`
  Initializes this parameter generator for a certain size.
  `final void`
  `init(int size, SecureRandom random)`
  Initializes this parameter generator for a certain size and source of randomness.
  `final void`
  `init(AlgorithmParameterSpec genParamSpec)`
  Initializes this parameter generator with a set of algorithm-specific parameter generation values.
  `final void`
  `init(AlgorithmParameterSpec genParamSpec, SecureRandom random)`
  Initializes this parameter generator with a set of algorithm-specific parameter generation values.

  ### Methods declared in class Object

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

- ## Constructor Details

  - ### AlgorithmParameterGenerator

    protected AlgorithmParameterGenerator(AlgorithmParameterGeneratorSpi paramGenSpi, Provider provider, String algorithm)
    Creates an `AlgorithmParameterGenerator` object.
    Parameters:
      `paramGenSpi` - the delegate
      `provider` - the provider
      `algorithm` - the algorithm

- ## Method Details

  - ### getAlgorithm

    public final String getAlgorithm()
    Returns the standard name of the algorithm this parameter generator is associated with.
    Returns:
      the string name of the algorithm.

  - ### getInstance

    public static AlgorithmParameterGenerator getInstance(String algorithm) throws NoSuchAlgorithmException
    Returns an `AlgorithmParameterGenerator` object for generating a set of parameters to be used with the specified algorithm.

    This method traverses the list of registered security providers, starting with the most preferred provider. A new `AlgorithmParameterGenerator` object encapsulating the `AlgorithmParameterGeneratorSpi` implementation from the first provider that supports the specified algorithm is returned.

    Note that the list of registered providers may be retrieved via the `Security.getProviders()` method.

    Implementation Note:
      The JDK Reference Implementation additionally uses the `jdk.security.provider.preferred` `Security` property to determine the preferred provider order for the specified algorithm. This may be different from the order of providers returned by `Security.getProviders()`.
    Parameters:
      `algorithm` - the name of the algorithm this parameter generator is associated with. See the AlgorithmParameterGenerator section in the Java Security Standard Algorithm Names Specification for information about standard algorithm names.
    Returns:
      the new `AlgorithmParameterGenerator` object
    Throws:
      `NoSuchAlgorithmException` - if no `Provider` supports an `AlgorithmParameterGeneratorSpi` implementation for the specified algorithm
      `NullPointerException` - if `algorithm` is `null`
    External Specifications
      - Java Security Standard Algorithm Names
    See Also:
      - `Provider`

  - ### getInstance

    public static AlgorithmParameterGenerator getInstance(String algorithm, String provider) throws NoSuchAlgorithmException, NoSuchProviderException
    Returns an `AlgorithmParameterGenerator` object for generating a set of parameters to be used with the specified algorithm.

    A new `AlgorithmParameterGenerator` object encapsulating the `AlgorithmParameterGeneratorSpi` implementation from the specified provider is returned. The specified provider must be registered in the security provider list.

    Note that the list of registered providers may be retrieved via the `Security.getProviders()` method.

    Parameters:
      `algorithm` - the name of the algorithm this parameter generator is associated with. See the AlgorithmParameterGenerator section in the Java Security Standard Algorithm Names Specification for information about standard algorithm names.
      `provider` - the string name of the `Provider`.
    Returns:
      the new `AlgorithmParameterGenerator` object
    Throws:
      `IllegalArgumentException` - if the provider name is `null` or empty
      `NoSuchAlgorithmException` - if an `AlgorithmParameterGeneratorSpi` implementation for the specified algorithm is not available from the specified provider
      `NoSuchProviderException` - if the specified provider is not registered in the security provider list
      `NullPointerException` - if `algorithm` is `null`
    External Specifications
      - Java Security Standard Algorithm Names
    See Also:
      - `Provider`

  - ### getInstance

    public static AlgorithmParameterGenerator getInstance(String algorithm, Provider provider) throws NoSuchAlgorithmException
    Returns an `AlgorithmParameterGenerator` object for generating a set of parameters to be used with the specified algorithm.

    A new `AlgorithmParameterGenerator` object encapsulating the `AlgorithmParameterGeneratorSpi` implementation from the specified provider is returned. Note that the specified provider does not have to be registered in the provider list.

    Parameters:
      `algorithm` - the string name of the algorithm this parameter generator is associated with. See the AlgorithmParameterGenerator section in the Java Security Standard Algorithm Names Specification for information about standard algorithm names.
      `provider` - the `Provider` object.
    Returns:
      the new `AlgorithmParameterGenerator` object
    Throws:
      `IllegalArgumentException` - if the specified provider is `null`
      `NoSuchAlgorithmException` - if an `AlgorithmParameterGeneratorSpi` implementation for the specified algorithm is not available from the specified `Provider` object
      `NullPointerException` - if `algorithm` is `null`
    Since:
      1.4
    External Specifications
      - Java Security Standard Algorithm Names
    See Also:
      - `Provider`

  - ### getProvider

    public final Provider getProvider()
    Returns the provider of this algorithm parameter generator object.
    Returns:
      the provider of this algorithm parameter generator object

  - ### init

    public final void init(int size)
    Initializes this parameter generator for a certain size. To create the parameters, the `SecureRandom` implementation of the highest-priority installed provider is used as the source of randomness. (If none of the installed providers supply an implementation of `SecureRandom`, a system-provided source of randomness is used.)
    Parameters:
      `size` - the size (number of bits).

  - ### init

    public final void init(int size, SecureRandom random)
    Initializes this parameter generator for a certain size and source of randomness.
    Parameters:
      `size` - the size (number of bits).
      `random` - the source of randomness.

  - ### init

    public final void init(AlgorithmParameterSpec genParamSpec) throws InvalidAlgorithmParameterException
    Initializes this parameter generator with a set of algorithm-specific parameter generation values. To generate the parameters, the `SecureRandom` implementation of the highest-priority installed provider is used as the source of randomness. (If none of the installed providers supply an implementation of `SecureRandom`, a system-provided source of randomness is used.)
    Parameters:
      `genParamSpec` - the set of algorithm-specific parameter generation values.
    Throws:
      `InvalidAlgorithmParameterException` - if the given parameter generation values are inappropriate for this parameter generator.

  - ### init

    public final void init(AlgorithmParameterSpec genParamSpec, SecureRandom random) throws InvalidAlgorithmParameterException
    Initializes this parameter generator with a set of algorithm-specific parameter generation values.
    Parameters:
      `genParamSpec` - the set of algorithm-specific parameter generation values.
      `random` - the source of randomness.
    Throws:
      `InvalidAlgorithmParameterException` - if the given parameter generation values are inappropriate for this parameter generator.

  - ### generateParameters

    public final AlgorithmParameters generateParameters()
    Generates the parameters.
    Returns:
      the new `AlgorithmParameters` object.