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