Package: groovy.lang

## [Java] 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
  Authors:
    John Wilson
    Graeme Rocher

- - ### Methods Summary

    Methods
    Type Params | Return Type | Name and 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 meta class
    `` | `List<MetaProperty>` | `getProperties()` Obtain a list of all meta properties available on this meta class
    `` | `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)`
    `` | `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 arguments.
    `` | `Object` | `invokeMethod(Object object, String methodName, Object arguments)` Invokes a method on the given object, with the given name and single argument.
    `` | `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, Object[] argTypes)`
    `` | `List<MetaMethod>` | `respondsTo(Object obj, String name)`
    `` | `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 Detail

    - #### public 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.

      See Also:
        MetaClassImpl
      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

    - #### public 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

    - #### public 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

    - #### public List<MetaMethod> getMethods()

      Obtain a list of all the meta methods available on this meta class

      See Also:
        MetaMethod
      Returns:
        A list of MetaMethod instances

    - #### public List<MetaProperty> getProperties()

      Obtain a list of all meta properties available on this meta class

      See Also:
        MetaProperty
      Returns:
        A list of MetaProperty instances

    - #### public 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.

      See Also:
        MetaClassImpl
      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

    - #### public 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

    - #### public Class getTheClass()

      Retrieves that Java Class that the attached Meta behaviours apply to

      Returns:
        The java.lang.Class instance

    - #### public 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

    - #### public 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

    - #### public 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.

      See Also:
        MissingMethodException
      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

    - #### public Object invokeMethod(Object object, String methodName, Object arguments)

      Invokes a method on the given object, with the given name and single argument.

      See Also:
        invokeMethod(Object, String, Object[])
      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

    - #### public 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

      See Also:
        MissingMethodException
      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

    - #### public 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

    - #### public 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

    - #### public 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.

      See Also:
        MetaClassImpl
      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

    - #### public 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.

      See Also:
        MetaClassImpl
      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