Java tutorial
/* * Copyright 2008 Google Inc. * * Licensed under the Apache License, Version 2.0 (the "License"); you may not * use this file except in compliance with the License. You may obtain a copy of * the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the * License for the specific language governing permissions and limitations under * the License. */ package com.google.gwt.user.client.ui; import com.google.gwt.event.logical.shared.HasValueChangeHandlers; import com.google.gwt.user.client.TakesValue; /** * Extends {@link TakesValue} to allow the value to be pulled back out, and to * throw {@link com.google.gwt.event.logical.shared.ValueChangeEvent * ValueChangeEvent} events. * <p> * An object that implements this interface should be a user input widget, where * the user and programmer can both set and get the object's value. It is * intended to provide a unified interface to widgets with "atomic" values, like * Strings and Dates. * * @param <T> the type of value */ public interface HasValue<T> extends TakesValue<T>, HasValueChangeHandlers<T> { /** * Gets this object's value. * * @return the object's value */ T getValue(); /** * Sets this object's value without firing any events. This should be * identical to calling setValue(value, false). * <p> * It is acceptable to fail assertions or throw (documented) unchecked * exceptions in response to bad values. * <p> * Widgets must accept null as a valid value. By convention, setting a widget to * null clears value, calling getValue() on a cleared widget returns null. Widgets * that can not be cleared (e.g. {@link CheckBox}) must find another valid meaning * for null input. * * @param value the object's new value */ void setValue(T value); /** * Sets this object's value. Fires * {@link com.google.gwt.event.logical.shared.ValueChangeEvent} when * fireEvents is true and the new value does not equal the existing value. * <p> * It is acceptable to fail assertions or throw (documented) unchecked * exceptions in response to bad values. * * @param value the object's new value * @param fireEvents fire events if true and value is new */ void setValue(T value, boolean fireEvents); }