Each proxy instance has an associated invocation handler. + * When a method is invoked on a proxy instance, the method + * invocation is encoded and dispatched to the {@code invoke} + * method of its invocation handler. + * + * @author Peter Jones + * @see Proxy + * @since 1.3 + */ +public interface InvocationHandler { + + /** + * 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. + * + * @param proxy the proxy instance that the method was invoked on + * + * @param method the {@code Method} instance corresponding to + * the interface method invoked on the proxy instance. The declaring + * class of the {@code 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. + * + * @param args an array of objects containing the values of the + * arguments passed in the method invocation on the proxy instance, + * or {@code null} if interface method takes no arguments. + * Arguments of primitive types are wrapped in instances of the + * appropriate primitive wrapper class, such as + * {@code java.lang.Integer} or {@code java.lang.Boolean}. + * + * @return 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 + * {@code null} and the interface method's return type is + * primitive, then a {@code 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 {@code 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 + * {@code throws} clause of the interface method or to the + * unchecked exception types {@code java.lang.RuntimeException} + * or {@code 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 {@code throws} clause of + * the interface method, then an + * {@link UndeclaredThrowableException} containing the + * exception that was thrown by this method will be thrown by the + * method invocation on the proxy instance. + * + * @see UndeclaredThrowableException + */ + public Object invoke(Object proxy, Method method, Object[] args) + throws Throwable; +}