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    1   /*
    2    * Copyright (c) 2005, Oracle and/or its affiliates. All rights reserved.
    3    * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
    4    *
    5    * This code is free software; you can redistribute it and/or modify it
    6    * under the terms of the GNU General Public License version 2 only, as
    7    * published by the Free Software Foundation.  Oracle designates this
    8    * particular file as subject to the "Classpath" exception as provided
    9    * by Oracle in the LICENSE file that accompanied this code.
   10    *
   11    * This code is distributed in the hope that it will be useful, but WITHOUT
   12    * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   13    * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   14    * version 2 for more details (a copy is included in the LICENSE file that
   15    * accompanied this code).
   16    *
   17    * You should have received a copy of the GNU General Public License version
   18    * 2 along with this work; if not, write to the Free Software Foundation,
   19    * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   20    *
   21    * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
   22    * or visit www.oracle.com if you need additional information or have any
   23    * questions.
   24    */
   25   package javax.swing;
   26   
   27   import java.awt.Container;
   28   import javax.swing.plaf.ComponentUI;
   29   import sun.awt.AppContext;
   30   
   31   /**
   32    * <code>LayoutStyle</code> provides information about how to position
   33    * components.  This class is primarily useful for visual tools and
   34    * layout managers.  Most developers will not need to use this class.
   35    * <p>
   36    * You typically don't set or create a
   37    * <code>LayoutStyle</code>.  Instead use the static method
   38    * <code>getInstance</code> to obtain the current instance.
   39    *
   40    * @since 1.6
   41    */
   42   public abstract class LayoutStyle {
   43       /**
   44        * Sets the shared instance of <code>LayoutStyle</code>.  Specifying
   45        * <code>null</code> results in using the <code>LayoutStyle</code> from
   46        * the current <code>LookAndFeel</code>.
   47        *
   48        * @param style the <code>LayoutStyle</code>, or <code>null</code>
   49        * @see #getInstance
   50        */
   51       public static void setInstance(LayoutStyle style) {
   52           synchronized(LayoutStyle.class) {
   53               if (style == null) {
   54                   AppContext.getAppContext().remove(LayoutStyle.class);
   55               }
   56               else {
   57                   AppContext.getAppContext().put(LayoutStyle.class, style);
   58               }
   59           }
   60       }
   61   
   62       /**
   63        * Returns the shared instance of <code>LayoutStyle</code>.  If an instance
   64        * has not been specified in <code>setInstance</code>, this will return
   65        * the <code>LayoutStyle</code> from the current <code>LookAndFeel</code>.
   66        *
   67        * @see LookAndFeel#getLayoutStyle
   68        * @return the shared instance of <code>LayoutStyle</code>
   69        */
   70       public static LayoutStyle getInstance() {
   71           LayoutStyle style;
   72           synchronized(LayoutStyle.class) {
   73               style = (LayoutStyle)AppContext.getAppContext().
   74                       get(LayoutStyle.class);
   75           }
   76           if (style == null) {
   77               return UIManager.getLookAndFeel().getLayoutStyle();
   78           }
   79           return style;
   80       }
   81   
   82   
   83       /**
   84        * <code>ComponentPlacement</code> is an enumeration of the
   85        * possible ways two components can be placed relative to each
   86        * other.  <code>ComponentPlacement</code> is used by the
   87        * <code>LayoutStyle</code> method <code>getPreferredGap</code>.  Refer to
   88        * <code>LayoutStyle</code> for more information.
   89        *
   90        * @see LayoutStyle#getPreferredGap(JComponent,JComponent,
   91        *      ComponentPlacement,int,Container)
   92        * @since 1.6
   93        */
   94       public enum ComponentPlacement {
   95           /**
   96            * Enumeration value indicating the two components are
   97            * visually related and will be placed in the same parent.
   98            * For example, a <code>JLabel</code> providing a label for a
   99            * <code>JTextField</code> is typically visually associated
  100            * with the <code>JTextField</code>; the constant <code>RELATED</code>
  101            * is used for this.
  102            */
  103           RELATED,
  104   
  105           /**
  106            * Enumeration value indicating the two components are
  107            * visually unrelated and will be placed in the same parent.
  108            * For example, groupings of components are usually visually
  109            * separated; the constant <code>UNRELATED</code> is used for this.
  110            */
  111           UNRELATED,
  112   
  113           /**
  114            * Enumeration value indicating the distance to indent a component
  115            * is being requested.  For example, often times the children of
  116            * a label will be horizontally indented from the label.  To determine
  117            * the preferred distance for such a gap use the
  118            * <code>INDENT</code> type.
  119            * <p>
  120            * This value is typically only useful with a direction of
  121            * <code>EAST</code> or <code>WEST</code>.
  122            */
  123           INDENT;
  124       }
  125   
  126   
  127       /**
  128        * Creates a new <code>LayoutStyle</code>.  You generally don't
  129        * create a <code>LayoutStyle</code>.  Instead use the method
  130        * <code>getInstance</code> to obtain the current
  131        * <code>LayoutStyle</code>.
  132        */
  133       public LayoutStyle() {
  134       }
  135   
  136       /**
  137        * Returns the amount of space to use between two components.
  138        * The return value indicates the distance to place
  139        * <code>component2</code> relative to <code>component1</code>.
  140        * For example, the following returns the amount of space to place
  141        * between <code>component2</code> and <code>component1</code>
  142        * when <code>component2</code> is placed vertically above
  143        * <code>component1</code>:
  144        * <pre>
  145        *   int gap = getPreferredGap(component1, component2,
  146        *                             ComponentPlacement.RELATED,
  147        *                             SwingConstants.NORTH, parent);
  148        * </pre>
  149        * The <code>type</code> parameter indicates the relation between
  150        * the two components.  If the two components will be contained in
  151        * the same parent and are showing similar logically related
  152        * items, use <code>RELATED</code>.  If the two components will be
  153        * contained in the same parent but show logically unrelated items
  154        * use <code>UNRELATED</code>.  Some look and feels may not
  155        * distinguish between the <code>RELATED</code> and
  156        * <code>UNRELATED</code> types.
  157        * <p>
  158        * The return value is not intended to take into account the
  159        * current size and position of <code>component2</code> or
  160        * <code>component1</code>.  The return value may take into
  161        * consideration various properties of the components.  For
  162        * example, the space may vary based on font size, or the preferred
  163        * size of the component.
  164        *
  165        * @param component1 the <code>JComponent</code>
  166        *               <code>component2</code> is being placed relative to
  167        * @param component2 the <code>JComponent</code> being placed
  168        * @param position the position <code>component2</code> is being placed
  169        *        relative to <code>component1</code>; one of
  170        *        <code>SwingConstants.NORTH</code>,
  171        *        <code>SwingConstants.SOUTH</code>,
  172        *        <code>SwingConstants.EAST</code> or
  173        *        <code>SwingConstants.WEST</code>
  174        * @param type how the two components are being placed
  175        * @param parent the parent of <code>component2</code>; this may differ
  176        *        from the actual parent and it may be <code>null</code>
  177        * @return the amount of space to place between the two components
  178        * @throws NullPointerException if <code>component1</code>,
  179        *         <code>component2</code> or <code>type</code> is
  180        *         <code>null</code>
  181        * @throws IllegalArgumentException if <code>position</code> is not
  182        *         one of <code>SwingConstants.NORTH</code>,
  183        *         <code>SwingConstants.SOUTH</code>,
  184        *         <code>SwingConstants.EAST</code> or
  185        *         <code>SwingConstants.WEST</code>
  186        * @see LookAndFeel#getLayoutStyle
  187        * @since 1.6
  188        */
  189       public abstract int getPreferredGap(JComponent component1,
  190                                           JComponent component2,
  191                                           ComponentPlacement type, int position,
  192                                           Container parent);
  193   
  194       /**
  195        * Returns the amount of space to place between the component and specified
  196        * edge of its parent.
  197        *
  198        * @param component the <code>JComponent</code> being positioned
  199        * @param position the position <code>component</code> is being placed
  200        *        relative to its parent; one of
  201        *        <code>SwingConstants.NORTH</code>,
  202        *        <code>SwingConstants.SOUTH</code>,
  203        *        <code>SwingConstants.EAST</code> or
  204        *        <code>SwingConstants.WEST</code>
  205        * @param parent the parent of <code>component</code>; this may differ
  206        *        from the actual parent and may be <code>null</code>
  207        * @return the amount of space to place between the component and specified
  208        *         edge
  209        * @throws IllegalArgumentException if <code>position</code> is not
  210        *         one of <code>SwingConstants.NORTH</code>,
  211        *         <code>SwingConstants.SOUTH</code>,
  212        *         <code>SwingConstants.EAST</code> or
  213        *         <code>SwingConstants.WEST</code>
  214        */
  215       public abstract int getContainerGap(JComponent component, int position,
  216                                           Container parent);
  217   }

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