com.google.common.reflect

Class AbstractInvocationHandler

java.lang.Object

com.google.common.reflect.AbstractInvocationHandler

All Implemented Interfaces:

InvocationHandler

@Beta
public abstract class AbstractInvocationHandler
extends Object
implements InvocationHandler

Abstract implementation of InvocationHandler that handles Object.equals(java.lang.Object), Object.hashCode() and Object.toString(). For example:

 class Unsupported extends AbstractInvocationHandler {
   protected Object handleInvocation(Object proxy, Method method, Object[] args) {
     throw new UnsupportedOperationException();
   }
 }

 CharSequence unsupported = Reflection.newProxy(CharSequence.class, new Unsupported());
 

Since:

12.0

Author:

Ben Yu

Constructor Summary

Constructors

Constructor and Description
AbstractInvocationHandler()

Method Summary

Modifier and Type	Method and Description
boolean	equals(Object obj) By default delegates to Object.equals(java.lang.Object) so instances are only equal if they are identical.
protected abstract Object	handleInvocation(Object proxy, Method method, Object[] args) invoke(java.lang.Object, java.lang.reflect.Method, java.lang.Object[]) delegates to this method upon any method invocation on the proxy instance, except Object.equals(java.lang.Object), Object.hashCode() and Object.toString().
int	hashCode() By default delegates to Object.hashCode().
Object	invoke(Object proxy, Method method, Object[] args) Processes a method invocation on a proxy instance and returns the result.
String	toString() By default delegates to Object.toString().

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Constructor Detail

AbstractInvocationHandler

public AbstractInvocationHandler()

Method Detail

invoke

public final Object invoke(Object proxy,
                           Method method,
                           @NullableDecl
                           Object[] args)
                    throws Throwable

Processes a method invocation on a proxy instance and returns the result. This method will be invoked on an invocation handler when a method is invoked on a proxy instance that it is associated with.

• proxy.hashCode() delegates to hashCode()
• proxy.toString() delegates to toString()
• proxy.equals(argument) returns true if:
  • proxy and argument are of the same type
  • and equals(java.lang.Object) returns true for the InvocationHandler of argument
• other method calls are dispatched to handleInvocation(java.lang.Object, java.lang.reflect.Method, java.lang.Object[]).

Specified by:

invoke in interface InvocationHandler

Parameters:

proxy - the proxy instance that the method was invoked on

method - the Method instance corresponding to the interface method invoked on the proxy instance. The declaring class of the Method object will be the interface that the method was declared in, which may be a superinterface of the proxy interface that the proxy class inherits the method through.

args - an array of objects containing the values of the arguments passed in the method invocation on the proxy instance, or null if interface method takes no arguments. Arguments of primitive types are wrapped in instances of the appropriate primitive wrapper class, such as java.lang.Integer or java.lang.Boolean.

Returns:

the value to return from the method invocation on the proxy instance. If the declared return type of the interface method is a primitive type, then the value returned by this method must be an instance of the corresponding primitive wrapper class; otherwise, it must be a type assignable to the declared return type. If the value returned by this method is null and the interface method's return type is primitive, then a NullPointerException will be thrown by the method invocation on the proxy instance. If the value returned by this method is otherwise not compatible with the interface method's declared return type as described above, a ClassCastException will be thrown by the method invocation on the proxy instance.

Throws:

Throwable - the exception to throw from the method invocation on the proxy instance. The exception's type must be assignable either to any of the exception types declared in the throws clause of the interface method or to the unchecked exception types java.lang.RuntimeException or java.lang.Error. If a checked exception is thrown by this method that is not assignable to any of the exception types declared in the throws clause of the interface method, then an UndeclaredThrowableException containing the exception that was thrown by this method will be thrown by the method invocation on the proxy instance.

See Also:

UndeclaredThrowableException

handleInvocation

protected abstract Object handleInvocation(Object proxy,
                                           Method method,
                                           Object[] args)
                                    throws Throwable

invoke(java.lang.Object, java.lang.reflect.Method, java.lang.Object[]) delegates to this method upon any method invocation on the proxy instance, except Object.equals(java.lang.Object), Object.hashCode() and Object.toString(). The result will be returned as the proxied method's return value.

Unlike invoke(java.lang.Object, java.lang.reflect.Method, java.lang.Object[]), args will never be null. When the method has no parameter, an empty array is passed in.

Throws:

Throwable

equals

public boolean equals(Object obj)

By default delegates to Object.equals(java.lang.Object) so instances are only equal if they are identical. proxy.equals(argument) returns true if:

• proxy and argument are of the same type
• and this method returns true for the InvocationHandler of argument

Subclasses can override this method to provide custom equality.

Overrides:

equals in class Object

Parameters:

obj - the reference object with which to compare.

Returns:

true if this object is the same as the obj argument; false otherwise.

See Also:

Object.hashCode(), HashMap

hashCode

public int hashCode()

By default delegates to Object.hashCode(). The dynamic proxies' hashCode() will delegate to this method. Subclasses can override this method to provide custom equality.

Overrides:

hashCode in class Object

Returns:

a hash code value for this object.

See Also:

Object.equals(java.lang.Object), System.identityHashCode(java.lang.Object)

toString

public String toString()

By default delegates to Object.toString(). The dynamic proxies' toString() will delegate to this method. Subclasses can override this method to provide custom string representation for the proxies.

Overrides:

toString in class Object

Returns:

a string representation of the object.