# Proxy

public class **Proxy** extends [Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html)  
implements [Serializable](https://developers.google.com/j2objc/javadoc/jre/reference/java/io/Serializable.html) `Proxy` provides static methods for creating dynamic proxy
classes and instances, and it is also the superclass of all
dynamic proxy classes created by those methods.

To create a proxy for some interface `Foo`:

```
     InvocationHandler handler = new MyInvocationHandler(...);
     Class proxyClass = Proxy.getProxyClass(
         Foo.class.getClassLoader(), new Class[] { Foo.class });
     Foo f = (Foo) proxyClass.
         getConstructor(new Class[] { InvocationHandler.class }).
         newInstance(new Object[] { handler });
 
```
or more simply:

```
     Foo f = (Foo) Proxy.newProxyInstance(Foo.class.getClassLoader(),
                                          new Class[] { Foo.class },
                                          handler);
 
```

A *dynamic proxy class* (simply referred to as a *proxy class* below) is a class that implements a list of interfaces
specified at runtime when the class is created, with behavior as
described below.

A *proxy interface* is such an interface that is implemented
by a proxy class.

A *proxy instance* is an instance of a proxy class.

Each proxy instance has an associated *invocation handler*
object, which implements the interface `https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/reflect/InvocationHandler.html`.
A method invocation on a proxy instance through one of its proxy
interfaces will be dispatched to the `https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/reflect/InvocationHandler.html#invoke(java.lang.Object,%20java.lang.reflect.Method,%20java.lang.Object[])` method of the instance's invocation handler, passing the proxy
instance, a `java.lang.reflect.Method` object identifying
the method that was invoked, and an array of type `Object`
containing the arguments. The invocation handler processes the
encoded method invocation as appropriate and the result that it
returns will be returned as the result of the method invocation on
the proxy instance.

A proxy class has the following properties:

- Proxy classes are public, final, and not abstract.
- The unqualified name of a proxy class is unspecified. The space of class names that begin with the string `"$Proxy"` should be, however, reserved for proxy classes.
- A proxy class extends `java.lang.reflect.Proxy`.
- A proxy class implements exactly the interfaces specified at its creation, in the same order.
- If a proxy class implements a non-public interface, then it will be defined in the same package as that interface. Otherwise, the package of a proxy class is also unspecified. Note that package sealing will not prevent a proxy class from being successfully defined in a particular package at runtime, and neither will classes already defined by the same class loader and the same package with particular signers.
- Since a proxy class implements all of the interfaces specified at its creation, invoking `getInterfaces` on its `Class` object will return an array containing the same list of interfaces (in the order specified at its creation), invoking `getMethods` on its `Class` object will return an array of `Method` objects that include all of the methods in those interfaces, and invoking `getMethod` will find methods in the proxy interfaces as would be expected.
- The `https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/reflect/Proxy.html#isProxyClass(java.lang.Class<?>)` method will return true if it is passed a proxy class-- a class returned by `Proxy.getProxyClass` or the class of an object returned by `Proxy.newProxyInstance`-- and false otherwise.
- The `java.security.ProtectionDomain` of a proxy class is the same as that of system classes loaded by the bootstrap class loader, such as `java.lang.Object`, because the code for a proxy class is generated by trusted system code. This protection domain will typically be granted `java.security.AllPermission`.
- Each proxy class has one public constructor that takes one argument, an implementation of the interface `https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/reflect/InvocationHandler.html`, to set the invocation handler for a proxy instance. Rather than having to use the reflection API to access the public constructor, a proxy instance can be also be created by calling the `https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/reflect/Proxy.html#newProxyInstance(java.lang.ClassLoader,%20java.lang.Class<?>[],%20java.lang.reflect.InvocationHandler)` method, which combines the actions of calling `https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/reflect/Proxy.html#getProxyClass(java.lang.ClassLoader,%20java.lang.Class<?>...)` with invoking the constructor with an invocation handler.

A proxy instance has the following properties:

- Given a proxy instance `proxy` and one of the interfaces implemented by its proxy class `Foo`, the following expression will return true:

           proxy instanceof Foo
       
  and the following cast operation will succeed (rather than throwing a `ClassCastException`):

           (Foo) proxy
       
- Each proxy instance has an associated invocation handler, the one that was passed to its constructor. The static `https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/reflect/Proxy.html#getInvocationHandler(java.lang.Object)` method will return the invocation handler associated with the proxy instance passed as its argument.
- An interface method invocation on a proxy instance will be encoded and dispatched to the invocation handler's `https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/reflect/InvocationHandler.html#invoke(java.lang.Object,%20java.lang.reflect.Method,%20java.lang.Object[])` method as described in the documentation for that method.
- An invocation of the `hashCode`, `equals`, or `toString` methods declared in `java.lang.Object` on a proxy instance will be encoded and dispatched to the invocation handler's `invoke` method in the same manner as interface method invocations are encoded and dispatched, as described above. The declaring class of the `Method` object passed to `invoke` will be `java.lang.Object`. Other public methods of a proxy instance inherited from `java.lang.Object` are not overridden by a proxy class, so invocations of those methods behave like they do for instances of `java.lang.Object`.

### Methods Duplicated in Multiple Proxy Interfaces

When two or more interfaces of a proxy class contain a method with
the same name and parameter signature, the order of the proxy class's
interfaces becomes significant. When such a *duplicate method*
is invoked on a proxy instance, the `Method` object passed
to the invocation handler will not necessarily be the one whose
declaring class is assignable from the reference type of the interface
that the proxy's method was invoked through. This limitation exists
because the corresponding method implementation in the generated proxy
class cannot determine which interface it was invoked through.
Therefore, when a duplicate method is invoked on a proxy instance,
the `Method` object for the method in the foremost interface
that contains the method (either directly or inherited through a
superinterface) in the proxy class's list of interfaces is passed to
the invocation handler's `invoke` method, regardless of the
reference type through which the method invocation occurred.

If a proxy interface contains a method with the same name and
parameter signature as the `hashCode`, `equals`,
or `toString` methods of `java.lang.Object`,
when such a method is invoked on a proxy instance, the
`Method` object passed to the invocation handler will have
`java.lang.Object` as its declaring class. In other words,
the public, non-final methods of `java.lang.Object`
logically precede all of the proxy interfaces for the determination of
which `Method` object to pass to the invocation handler.

Note also that when a duplicate method is dispatched to an
invocation handler, the `invoke` method may only throw
checked exception types that are assignable to one of the exception
types in the `throws` clause of the method in *all* of
the proxy interfaces that it can be invoked through. If the
`invoke` method throws a checked exception that is not
assignable to any of the exception types declared by the method in one
of the proxy interfaces that it can be invoked through, then an
unchecked `UndeclaredThrowableException` will be thrown by
the invocation on the proxy instance. This restriction means that not
all of the exception types returned by invoking
`getExceptionTypes` on the `Method` object
passed to the `invoke` method can necessarily be thrown
successfully by the `invoke` method.

##### See Also

- `https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/reflect/InvocationHandler.html`

### Field Summary

|---|---|---|
| protected [InvocationHandler](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/reflect/InvocationHandler.html) | [h](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/reflect/Proxy.html#h) | the invocation handler for this proxy instance. |

### Protected Constructor Summary

|---|---|
|   | [Proxy](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/reflect/Proxy.html#Proxy(java.lang.reflect.InvocationHandler))([InvocationHandler](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/reflect/InvocationHandler.html) h) Constructs a new `Proxy` instance from a subclass (typically, a dynamic proxy class) with the specified value for its invocation handler. |

### Public Method Summary

|---|---|
| boolean | [equals](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/reflect/Proxy.html#equals(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) obj) Compares this instance with the specified object and indicates if they are equal. |
| static [InvocationHandler](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/reflect/InvocationHandler.html) | [getInvocationHandler](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/reflect/Proxy.html#getInvocationHandler(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) proxy) Returns the invocation handler for the specified proxy instance. |
| static [Class](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Class.html)\<?\> | [getProxyClass](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/reflect/Proxy.html#getProxyClass(java.lang.ClassLoader,%20java.lang.Class<?>...))([ClassLoader](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/ClassLoader.html) loader, [Class...](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Class.html)\<?\> interfaces) Returns the `java.lang.Class` object for a proxy class given a class loader and an array of interfaces. |
| int | [hashCode](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/reflect/Proxy.html#hashCode())() Returns an integer hash code for this object. |
| static boolean | [isProxyClass](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/reflect/Proxy.html#isProxyClass(java.lang.Class<?>))([Class](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Class.html)\<?\> cl) Returns true if and only if the specified class was dynamically generated to be a proxy class using the `getProxyClass` method or the `newProxyInstance` method. |
| static [Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) | [newProxyInstance](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/reflect/Proxy.html#newProxyInstance(java.lang.ClassLoader,%20java.lang.Class<?>[],%20java.lang.reflect.InvocationHandler))([ClassLoader](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/ClassLoader.html) loader, [Class\[\]](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Class.html)\<?\> interfaces, [InvocationHandler](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/reflect/InvocationHandler.html) h) Returns an instance of a proxy class for the specified interfaces that dispatches method invocations to the specified invocation handler. |
| [String](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/String.html) | [toString](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/reflect/Proxy.html#toString())() Returns a string containing a concise, human-readable description of this object. |

### Inherited Method Summary

From class [java.lang.Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html)

|---|---|
| [Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) | [clone](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#clone())() Creates and returns a copy of this `Object`. |
| boolean | [equals](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#equals(java.lang.Object))([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) obj) Compares this instance with the specified object and indicates if they are equal. |
| void | [finalize](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#finalize())() Invoked when the garbage collector has detected that this instance is no longer reachable. |
| final [Class](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Class.html)\<?\> | [getClass](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#getClass())() Returns the unique instance of `https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Class.html` that represents this object's class. |
| int | [hashCode](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#hashCode())() Returns an integer hash code for this object. |
| final void | [notify](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#notify())() Causes a thread which is waiting on this object's monitor (by means of calling one of the `wait()` methods) to be woken up. |
| final void | [notifyAll](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#notifyAll())() Causes all threads which are waiting on this object's monitor (by means of calling one of the `wait()` methods) to be woken up. |
| [String](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/String.html) | [toString](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#toString())() Returns a string containing a concise, human-readable description of this object. |
| final void | [wait](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#wait(long,%20int))(long timeout, int nanos) Causes the calling thread to wait until another thread calls the `notify()` or `notifyAll()` method of this object or until the specified timeout expires. |
| final void | [wait](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#wait(long))(long timeout) Causes the calling thread to wait until another thread calls the `notify()` or `notifyAll()` method of this object or until the specified timeout expires. |
| final void | [wait](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#wait())() Causes the calling thread to wait until another thread calls the `notify()` or `notifyAll()` method of this object. |

## Fields

#### protected [InvocationHandler](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/reflect/InvocationHandler.html)
**h**

the invocation handler for this proxy instance.

## Protected Constructors

#### protected
**Proxy**
([InvocationHandler](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/reflect/InvocationHandler.html) h)

Constructs a new `Proxy` instance from a subclass
(typically, a dynamic proxy class) with the specified value
for its invocation handler.

##### Parameters

| h | the invocation handler for this proxy instance |
|---|---|

## Public Methods

#### public boolean
**equals**
([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) obj)

Compares this instance with the specified object and indicates if they
are equal. In order to be equal, `o` must represent the same object
as this instance using a class-specific comparison. The general contract
is that this comparison should be reflexive, symmetric, and transitive.
Also, no object reference other than null is equal to null.

The default implementation returns `true` only if `this ==
o`. See [Writing a correct
`equals` method](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#writing_equals)
if you intend implementing your own `equals` method.

The general contract for the `equals` and `https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#hashCode()` methods is that if `equals` returns `true` for
any two objects, then `hashCode()` must return the same value for
these objects. This means that subclasses of `Object` usually
override either both methods or neither of them.

##### Parameters

| obj | the object to compare this instance with. |
|---|---|

##### Returns

- `true` if the specified object is equal to this `Object`; `false` otherwise.

#### public static [InvocationHandler](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/reflect/InvocationHandler.html)
**getInvocationHandler**
([Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html) proxy)

Returns the invocation handler for the specified proxy instance.

##### Parameters

| proxy | the proxy instance to return the invocation handler for |
|---|---|

##### Returns

- the invocation handler for the proxy instance

##### Throws

| [IllegalArgumentException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/IllegalArgumentException.html) | if the argument is not a proxy instance |
|---|---|

#### public static [Class](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Class.html)\<?\>
**getProxyClass**
([ClassLoader](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/ClassLoader.html) loader, [Class...](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Class.html)\<?\> interfaces)

Returns the `java.lang.Class` object for a proxy class
given a class loader and an array of interfaces. The proxy class
will be defined by the specified class loader and will implement
all of the supplied interfaces. If a proxy class for the same
permutation of interfaces has already been defined by the class
loader, then the existing proxy class will be returned; otherwise,
a proxy class for those interfaces will be generated dynamically
and defined by the class loader.

There are several restrictions on the parameters that may be
passed to `Proxy.getProxyClass`:

- All of the `Class` objects in the `interfaces` array must represent interfaces, not classes or primitive types.
- No two elements in the `interfaces` array may refer to identical `Class` objects.
- All of the interface types must be visible by name through the specified class loader. In other words, for class loader `cl` and every interface `i`, the following expression must be true:

  ```
       Class.forName(i.getName(), false, cl) == i
   
  ```
- All non-public interfaces must be in the same package; otherwise, it would not be possible for the proxy class to implement all of the interfaces, regardless of what package it is defined in.
- For any set of member methods of the specified interfaces that have the same signature:
  - If the return type of any of the methods is a primitive type or void, then all of the methods must have that same return type.
  - Otherwise, one of the methods must have a return type that is assignable to all of the return types of the rest of the methods.
- The resulting proxy class must not exceed any limits imposed on classes by the virtual machine. For example, the VM may limit the number of interfaces that a class may implement to 65535; in that case, the size of the `interfaces` array must not exceed 65535.

If any of these restrictions are violated,
`Proxy.getProxyClass` will throw an
`IllegalArgumentException`. If the `interfaces`
array argument or any of its elements are `null`, a
`NullPointerException` will be thrown.

Note that the order of the specified proxy interfaces is
significant: two requests for a proxy class with the same combination
of interfaces but in a different order will result in two distinct
proxy classes.

##### Parameters

| loader | the class loader to define the proxy class |
| interfaces | the list of interfaces for the proxy class to implement |
|---|---|

##### Returns

- a proxy class that is defined in the specified class loader and that implements the specified interfaces

##### Throws

| [IllegalArgumentException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/IllegalArgumentException.html) | if any of the restrictions on the parameters that may be passed to `getProxyClass` are violated |
| [NullPointerException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/NullPointerException.html) | if the `interfaces` array argument or any of its elements are `null` |
|---|---|

#### public int
**hashCode**
()

Returns an integer hash code for this object. By contract, any two
objects for which `https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#equals(java.lang.Object)` returns `true` must return
the same hash code value. This means that subclasses of `Object`
usually override both methods or neither method.

Note that hash values must not change over time unless information used in equals
comparisons also changes.

See [Writing a correct
`hashCode` method](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#writing_hashCode)
if you intend implementing your own `hashCode` method.

##### Returns

- this object's hash code.

#### public static boolean
**isProxyClass**
([Class](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Class.html)\<?\> cl)

Returns true if and only if the specified class was dynamically
generated to be a proxy class using the `getProxyClass`
method or the `newProxyInstance` method.

The reliability of this method is important for the ability
to use it to make security decisions, so its implementation should
not just test if the class in question extends `Proxy`.

##### Parameters

| cl | the class to test |
|---|---|

##### Returns

- `true` if the class is a proxy class and `false` otherwise

##### Throws

| [NullPointerException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/NullPointerException.html) | if `cl` is `null` |
|---|---|

#### public static [Object](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html)
**newProxyInstance**
([ClassLoader](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/ClassLoader.html) loader, [Class\[\]](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Class.html)\<?\> interfaces, [InvocationHandler](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/reflect/InvocationHandler.html) h)

Returns an instance of a proxy class for the specified interfaces
that dispatches method invocations to the specified invocation
handler. This method is equivalent to:

```
     Proxy.getProxyClass(loader, interfaces).
         getConstructor(new Class[] { InvocationHandler.class }).
         newInstance(new Object[] { handler });
 
```

`Proxy.newProxyInstance` throws
`IllegalArgumentException` for the same reasons that
`Proxy.getProxyClass` does.

##### Parameters

| loader | the class loader to define the proxy class |
| interfaces | the list of interfaces for the proxy class to implement |
| h | the invocation handler to dispatch method invocations to |
|---|---|

##### Returns

- a proxy instance with the specified invocation handler of a proxy class that is defined by the specified class loader and that implements the specified interfaces

##### Throws

| [IllegalArgumentException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/IllegalArgumentException.html) | if any of the restrictions on the parameters that may be passed to `getProxyClass` are violated |
| [NullPointerException](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/NullPointerException.html) | if the `interfaces` array argument or any of its elements are `null`, or if the invocation handler, `h`, is `null` |
|---|---|

#### public [String](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/String.html)
**toString**
()

Returns a string containing a concise, human-readable description of this
object. Subclasses are encouraged to override this method and provide an
implementation that takes into account the object's type and data. The
default implementation is equivalent to the following expression:

```
   getClass().getName() + '@' + Integer.toHexString(hashCode())
```

See [Writing a useful
`toString` method](https://developers.google.com/j2objc/javadoc/jre/reference/java/lang/Object.html#writing_toString)
if you intend implementing your own `toString` method.

##### Returns

- a printable representation of this object.