    001// Copyright 2006-2013 The Apache Software Foundation
    002//
    003// Licensed under the Apache License, Version 2.0 (the "License");
    004// you may not use this file except in compliance with the License.
    005// You may obtain a copy of the License at
    006//
    007//     http://www.apache.org/licenses/LICENSE-2.0
    008//
    009// Unless required by applicable law or agreed to in writing, software
    010// distributed under the License is distributed on an "AS IS" BASIS,
    011// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    012// See the License for the specific language governing permissions and
    013// limitations under the License.
    014
    015package org.apache.tapestry5;
    016
    017import org.apache.tapestry5.ioc.AnnotationProvider;
    018
    019/**
    020 * A binding is a connection between a component and its container (another component), that allows the embedded
    021 * component to gain access to <em>resources</em> defined by the container. Resources can represent any kind of value
    022 * that can be obtained from the parent component, but is often a JavaBean property that can be read and updated.
    023 * Different implementations of Binding are used to access different kinds of resources of the container.
    024 * <p/>
    025 * A binding ultimately must provide access to the underlying annotations. In most cases, there are no annotations, but
    026 * bindings that ultimate invoke methods or read and update fields must provide access to those annotations.
    027 */
    028public interface Binding extends AnnotationProvider
    029{
    030    /**
    031     * Reads the current value of the property (or other resource). When reading properties of objects that are
    032     * primitive types, this will return an instance of the wrapper type. In some cases, a binding is read only and this
    033     * method will throw a runtime exception.
    034     */
    035    Object get();
    036
    037    /**
    038     * Updates the current value. Most types of bindings are read-only, and this method will throw a runtime exception.
    039     * It is the caller's responsibility to ensure that the value passed in is of the appropriate type.
    040     *
    041     * @param value
    042     */
    043    void set(Object value);
    044
    045    /**
    046     * Returns true if the value of the binding does not ever change. Components will often cache such values
    047     * aggressively.
    048     */
    049    boolean isInvariant();
    050
    051    /**
    052     * Returns the type of the binding, either the type of resource exposed by the binding, or the type of the property
    053     * bound.
    054     */
    055    Class getBindingType();
    056}