2.1/user/src/com/google/gwt/user/client/ui/WidgetIterators.java

/*
 * Copyright 2007 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 java.util.Iterator;
import java.util.NoSuchElementException;

/**
 * A collection of convenience factories for creating iterators for widgets.
 * This mostly helps developers support {@link HasWidgets} without having to
 * implement their own {@link Iterator}.
 */
class WidgetIterators {

  private static Widget[] copyWidgetArray(final Widget[] widgets) {
    final Widget[] clone = new Widget[widgets.length];
    for (int i = 0; i < widgets.length; i++) {
      clone[i] = widgets[i];
    }
    return clone;
  }

  /**
   * Wraps an array of widgets to be returned during iteration.
   * <code>null</code> is allowed in the array and will be skipped during
   * iteration.
   * 
   * @param container the container of the widgets in <code>contained</code>
   * @param contained the array of widgets
   * @return the iterator
   */
  static final Iterator<Widget> createWidgetIterator(final HasWidgets container,
      final Widget[] contained) {
    return new Iterator<Widget>() {
      int index = -1, last = -1;
      boolean widgetsWasCopied = false;
      Widget[] widgets = contained;

      {
        gotoNextIndex();
      }

      private void gotoNextIndex() {
        ++index;
        while (index < contained.length) {
          if (contained[index] != null) {
            return;
          }
          ++index;
        }
      }

      public boolean hasNext() {
        return (index < contained.length);
      }

      public Widget next() {
        if (!hasNext()) {
          throw new NoSuchElementException();
        }
        last = index;
        final Widget w = contained[index];
        gotoNextIndex();
        return w;
      }

      public void remove() {
        if (last < 0) {
          throw new IllegalStateException();
        }

        if (!widgetsWasCopied) {
          widgets = copyWidgetArray(widgets);
          widgetsWasCopied = true;
        }

        container.remove(contained[last]);
        last = -1;
      }
    };
  }

  private WidgetIterators() {
    // Not instantiable.
  }
}