/* * Copyright 1999-2005 The Apache Software Foundation. *  * 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 org.apache.log4j.lf5.viewer;import java.awt.*;import java.awt.event.AdjustmentEvent;import java.awt.event.AdjustmentListener;/** * An AdjustmentListener which ensures that an Adjustable (e.g. a Scrollbar) * will "track" when the Adjustable expands. * For example, when a vertical scroll bar is at its bottom anchor, * the scrollbar will remain at the bottom.  When the vertical scroll bar * is at any other location, then no tracking will happen. * An instance of this class should only listen to one Adjustable as * it retains state information about the Adjustable it listens to. * * @author Richard Wan */// Contributed by ThoughtWorks Inc.public class TrackingAdjustmentListener implements AdjustmentListener {  //--------------------------------------------------------------------------  //   Constants:  //--------------------------------------------------------------------------  //--------------------------------------------------------------------------  //   Protected Variables:  //--------------------------------------------------------------------------  protected int _lastMaximum = -1;  //--------------------------------------------------------------------------  //   Private Variables:  //--------------------------------------------------------------------------  //--------------------------------------------------------------------------  //   Constructors:  //--------------------------------------------------------------------------  //--------------------------------------------------------------------------  //   Public Methods:  //--------------------------------------------------------------------------  public void adjustmentValueChanged(AdjustmentEvent e) {    Adjustable bar = e.getAdjustable();    int currentMaximum = bar.getMaximum();    if (bar.getMaximum() == _lastMaximum) {      return; // nothing to do, the adjustable has not expanded    }    int bottom = bar.getValue() + bar.getVisibleAmount();    if (bottom + bar.getUnitIncrement() >= _lastMaximum) {      bar.setValue(bar.getMaximum()); // use the most recent maximum    }    _lastMaximum = currentMaximum;  }  //--------------------------------------------------------------------------  //   Protected Methods:  //--------------------------------------------------------------------------  //--------------------------------------------------------------------------  //   Private Methods:  //--------------------------------------------------------------------------  //--------------------------------------------------------------------------  //   Nested Top-Level Classes or Interfaces  //--------------------------------------------------------------------------}