Package groovy.lang

# Interface MetaObjectProtocol

All Known Subinterfaces:
  `AdaptingMetaClass`, `MetaClass`, `MutableMetaClass`

All Known Implementing Classes:
  `ClosureMetaClass`, `DelegatingMetaClass`, `ExpandoMetaClass`, `HandleMetaClass`, `MetaClassImpl`, `MixedInMetaClass`, `MockProxyMetaClass`, `OwnedMetaClass`, `ProxyMetaClass`

public interface MetaObjectProtocol

An interface that defines the API usable by clients of Groovy's Meta Object Protocol (MOP). These methods are implemented by the reference implementation of the `MetaClass` interface.

See Also:
  - `MetaClassImpl`

- ## Method Summary

  Modifier and Type
  Method
  Description
  `Object`
  `getAttribute(Object object, String attribute)`
  Retrieves an attribute of an instance of the class returned by the getTheClass() method.
  `MetaMethod`
  `getMetaMethod(String name, Object[] args)`
  Retrieves an instance MetaMethod for the given name and argument values, using the types of the argument values to establish the chosen MetaMethod
  `MetaProperty`
  `getMetaProperty(String name)`
  Returns a MetaProperty for the given name or null if it doesn't exist
  `List<MetaMethod>`
  `getMethods()`
  Obtain a list of all the meta methods available on this metaclass
  `List<MetaProperty>`
  `getProperties()`
  Obtain a list of all meta properties available on this metaclass
  `Object`
  `getProperty(Object object, String property)`
  Retrieves a property of an instance of the class returned by the getTheClass() method.
  `MetaMethod`
  `getStaticMetaMethod(String name, Object[] args)`
  Retrieves a static MetaMethod for the given name and argument values, using the types of the arguments to establish the chosen MetaMethod
  `Class`
  `getTheClass()`
  Retrieves that Java Class that the attached Meta behaviours apply to
  `MetaProperty`
  `hasProperty(Object obj, String name)`
  Returns true of the implementing MetaClass has a property of the given name
  `Object`
  `invokeConstructor(Object[] arguments)`
  Invokes a constructor for the given arguments.
  `Object`
  `invokeMethod(Object object, String methodName, Object arguments)`
  Invokes a method on the given object, with the given name and single argument.
  `Object`
  `invokeMethod(Object object, String methodName, Object[] arguments)`
  Invokes a method on the given Object with the given name and arguments.
  `Object`
  `invokeStaticMethod(Object object, String methodName, Object[] arguments)`
  Invokes a static method on the given Object with the given name and arguments.
  `List<MetaMethod>`
  `respondsTo(Object obj, String name)`
  Returns an object satisfying Groovy truth if the implementing MetaClass responds to a method with the given name regardless of arguments.
  `List<MetaMethod>`
  `respondsTo(Object obj, String name, Object[] argTypes)`
  Returns an object satisfying Groovy truth if the implementing MetaClass responds to a method with the given name and arguments types.
  `void`
  `setAttribute(Object object, String attribute, Object newValue)`
  Sets an attribute of an instance of the class returned by the getTheClass() method.
  `void`
  `setProperty(Object object, String property, Object newValue)`
  Sets a property of an instance of the class returned by the getTheClass() method.

- ## Method Details

  - ### getProperties

    List<MetaProperty> getProperties()
    Obtain a list of all meta properties available on this metaclass
    Returns:
      A list of MetaProperty instances
    See Also:
      - `MetaProperty`

  - ### getMethods

    List<MetaMethod> getMethods()
    Obtain a list of all the meta methods available on this metaclass
    Returns:
      A list of MetaMethod instances
    See Also:
      - `MetaMethod`

  - ### respondsTo

    List<MetaMethod> respondsTo(Object obj, String name, Object[] argTypes)

    Returns an object satisfying Groovy truth if the implementing MetaClass responds to a method with the given name and arguments types.

    Note that this method's return value is based on realised methods and does not take into account objects or classes that implement invokeMethod or methodMissing

    This method is "safe" in that it will always return a value and never throw an exception

    Parameters:
      `obj` - The object to inspect
      `name` - The name of the method of interest
      `argTypes` - The argument types to match against
    Returns:
      A List of MetaMethods matching the argument types which will be empty if no matching methods exist

  - ### respondsTo

    List<MetaMethod> respondsTo(Object obj, String name)

    Returns an object satisfying Groovy truth if the implementing MetaClass responds to a method with the given name regardless of arguments. In other words this method will return for foo() and foo(String).

    Note that this method's return value is based on realised methods and does not take into account objects or classes that implement invokeMethod or methodMissing

    This method is "safe" in that it will always return a value and never throw an exception

    Parameters:
      `obj` - The object to inspect
      `name` - The name of the method of interest
    Returns:
      A List of MetaMethods which will be empty if no methods with the given name exist

  - ### hasProperty

    MetaProperty hasProperty(Object obj, String name)

    Returns true of the implementing MetaClass has a property of the given name

    Note that this method will only return true for realised properties and does not take into account implementation of getProperty or propertyMissing

    Parameters:
      `obj` - The object to inspect
      `name` - The name of the property
    Returns:
      The MetaProperty or null if it doesn't exist

  - ### getMetaProperty

    MetaProperty getMetaProperty(String name)
    Returns a MetaProperty for the given name or null if it doesn't exist
    Parameters:
      `name` - The name of the MetaProperty
    Returns:
      A MetaProperty or null

  - ### getStaticMetaMethod

    MetaMethod getStaticMetaMethod(String name, Object[] args)
    Retrieves a static MetaMethod for the given name and argument values, using the types of the arguments to establish the chosen MetaMethod
    Parameters:
      `name` - The name of the MetaMethod
      `args` - The argument types
    Returns:
      A MetaMethod or null if it doesn't exist

  - ### getMetaMethod

    MetaMethod getMetaMethod(String name, Object[] args)
    Retrieves an instance MetaMethod for the given name and argument values, using the types of the argument values to establish the chosen MetaMethod
    Parameters:
      `name` - The name of the MetaMethod
      `args` - Array containing - 1) the argument values (using which their types are then inferred), or 2) the corresponding argument types
    Returns:
      A MetaMethod or null if it doesn't exist

  - ### getTheClass

    Class getTheClass()
    Retrieves that Java Class that the attached Meta behaviours apply to
    Returns:
      The java.lang.Class instance

  - ### invokeConstructor

    Object invokeConstructor(Object[] arguments)
    Invokes a constructor for the given arguments. The MetaClass will attempt to pick the best argument which matches the types of the objects passed within the arguments array
    Parameters:
      `arguments` - The arguments to the constructor
    Returns:
      An instance of the java.lang.Class that this MetaObjectProtocol object applies to

  - ### invokeMethod

    Object invokeMethod(Object object, String methodName, Object[] arguments)
    Invokes a method on the given Object with the given name and arguments. The MetaClass will attempt to pick the best method for the given name and arguments. If a method cannot be invoked a MissingMethodException will be thrown.
    Parameters:
      `object` - The instance which the method is invoked on
      `methodName` - The name of the method
      `arguments` - The arguments to the method
    Returns:
      The return value of the method which is null if the return type is void
    See Also:
      - `MissingMethodException`

  - ### invokeMethod

    Object invokeMethod(Object object, String methodName, Object arguments)
    Invokes a method on the given object, with the given name and single argument.
    Parameters:
      `object` - The Object to invoke the method on
      `methodName` - The name of the method
      `arguments` - The argument to the method
    Returns:
      The return value of the method which is null if the return type is void
    See Also:
      - `invokeMethod(Object, String, Object[])`

  - ### invokeStaticMethod

    Object invokeStaticMethod(Object object, String methodName, Object[] arguments)
    Invokes a static method on the given Object with the given name and arguments.

    The Object can either be an instance of the class that this MetaObjectProtocol instance applies to or the java.lang.Class instance itself. If a method cannot be invoked a MissingMethodException is will be thrown

    Parameters:
      `object` - An instance of the class returned by the getTheClass() method or the class itself
      `methodName` - The name of the method
      `arguments` - The arguments to the method
    Returns:
      The return value of the method which is null if the return type is void
    See Also:
      - `MissingMethodException`

  - ### getProperty

    Object getProperty(Object object, String property)
    Retrieves a property of an instance of the class returned by the getTheClass() method.

    What this means is largely down to the MetaClass implementation, however the default case would result in an attempt to invoke a JavaBean getter, or if no such getter exists a public field of the instance.

    Parameters:
      `object` - An instance of the class returned by the getTheClass() method
      `property` - The name of the property to retrieve the value for
    Returns:
      The properties value
    See Also:
      - `MetaClassImpl`

  - ### setProperty

    void setProperty(Object object, String property, Object newValue)
    Sets a property of an instance of the class returned by the getTheClass() method.

    What this means is largely down to the MetaClass implementation, however the default case would result in an attempt to invoke a JavaBean setter, or if no such setter exists to set a public field of the instance.

    Parameters:
      `object` - An instance of the class returned by the getTheClass() method
      `property` - The name of the property to set
      `newValue` - The new value of the property
    See Also:
      - `MetaClassImpl`

  - ### getAttribute

    Object getAttribute(Object object, String attribute)
    Retrieves an attribute of an instance of the class returned by the getTheClass() method.

    What this means is largely down to the MetaClass implementation, however the default case would result in attempt to read a field of the instance.

    Parameters:
      `object` - An instance of the class returned by the getTheClass() method
      `attribute` - The name of the attribute to retrieve the value for
    Returns:
      The attribute value
    See Also:
      - `MetaClassImpl`

  - ### setAttribute

    void setAttribute(Object object, String attribute, Object newValue)
    Sets an attribute of an instance of the class returned by the getTheClass() method.

    What this means is largely down to the MetaClass implementation, however the default case would result in an attempt to set a field of the instance.

    Parameters:
      `object` - An instance of the class returned by the getTheClass() method
      `attribute` - The name of the attribute to set
      `newValue` - The new value of the attribute
    See Also:
      - `MetaClassImpl`