JDK8/Java8源码在线阅读

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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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 */
package javax.swing.text;

import java.awt.Shape;

/**
 * <code>NavigationFilter</code> can be used to restrict where the cursor can
 * be positioned. When the default cursor positioning actions attempt to
 * reposition the cursor they will call into the
 * <code>NavigationFilter</code>, assuming
 * the <code>JTextComponent</code> has a non-null
 * <code>NavigationFilter</code> set. In this manner
 * the <code>NavigationFilter</code> can effectively restrict where the
 * cursor can be positioned. Similarly <code>DefaultCaret</code> will call
 * into the <code>NavigationFilter</code> when the user is changing the
 * selection to further restrict where the cursor can be positioned.
 * <p>
 * Subclasses can conditionally call into supers implementation to restrict
 * where the cursor can be placed, or call directly into the
 * <code>FilterBypass</code>.
 *
 * @see javax.swing.text.Caret
 * @see javax.swing.text.DefaultCaret
 * @see javax.swing.text.View
 *
 * @since 1.4
 */
public class NavigationFilter {
    /**
     * Invoked prior to the Caret setting the dot. The default implementation
     * calls directly into the <code>FilterBypass</code> with the passed
     * in arguments. Subclasses may wish to conditionally
     * call super with a different location, or invoke the necessary method
     * on the <code>FilterBypass</code>
     *
     * @param fb FilterBypass that can be used to mutate caret position
     * @param dot the position &gt;= 0
     * @param bias Bias to place the dot at
     */
    public void setDot(FilterBypass fb, int dot, Position.Bias bias) {
        fb.setDot(dot, bias);
    }

    /**
     * Invoked prior to the Caret moving the dot. The default implementation
     * calls directly into the <code>FilterBypass</code> with the passed
     * in arguments. Subclasses may wish to conditionally
     * call super with a different location, or invoke the necessary
     * methods on the <code>FilterBypass</code>.
     *
     * @param fb FilterBypass that can be used to mutate caret position
     * @param dot the position &gt;= 0
     * @param bias Bias for new location
     */
    public void moveDot(FilterBypass fb, int dot, Position.Bias bias) {
        fb.moveDot(dot, bias);
    }

    /**
     * Returns the next visual position to place the caret at from an
     * existing position. The default implementation simply forwards the
     * method to the root View. Subclasses may wish to further restrict the
     * location based on additional criteria.
     *
     * @param text JTextComponent containing text
     * @param pos Position used in determining next position
     * @param bias Bias used in determining next position
     * @param direction the direction from the current position that can
     *  be thought of as the arrow keys typically found on a keyboard.
     *  This will be one of the following values:
     * <ul>
     * <li>SwingConstants.WEST
     * <li>SwingConstants.EAST
     * <li>SwingConstants.NORTH
     * <li>SwingConstants.SOUTH
     * </ul>
     * @param biasRet Used to return resulting Bias of next position
     * @return the location within the model that best represents the next
     *  location visual position
     * @exception BadLocationException
     * @exception IllegalArgumentException if <code>direction</code>
     *          doesn't have one of the legal values above
     */
    public int getNextVisualPositionFrom(JTextComponent text, int pos,
                                         Position.Bias bias, int direction,
                                         Position.Bias[] biasRet)
                                           throws BadLocationException {
        return text.getUI().getNextVisualPositionFrom(text, pos, bias,
                                                      direction, biasRet);
    }


    /**
     * Used as a way to circumvent calling back into the caret to
     * position the cursor. Caret implementations that wish to support
     * a NavigationFilter must provide an implementation that will
     * not callback into the NavigationFilter.
     * @since 1.4
     */
    public static abstract class FilterBypass {
        /**
         * Returns the Caret that is changing.
         *

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