JDK14/Java14源码在线阅读

/*
 * Copyright (c) 2006, Oracle and/or its affiliates. All rights reserved.
 * 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
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package javax.swing.filechooser;

import java.io.File;
import java.util.Locale;

/**
 * An implementation of {@code FileFilter} that filters using a
 * specified set of extensions. The extension for a file is the
 * portion of the file name after the last ".". Files whose name does
 * not contain a "." have no file name extension. File name extension
 * comparisons are case insensitive.
 * <p>
 * The following example creates a
 * {@code FileNameExtensionFilter} that will show {@code jpg} files:
 * <pre>
 * FileFilter filter = new FileNameExtensionFilter("JPEG file", "jpg", "jpeg");
 * JFileChooser fileChooser = ...;
 * fileChooser.addChoosableFileFilter(filter);
 * </pre>
 *
 * @see FileFilter
 * @see javax.swing.JFileChooser#setFileFilter
 * @see javax.swing.JFileChooser#addChoosableFileFilter
 * @see javax.swing.JFileChooser#getFileFilter
 *
 * @since 1.6
 */
public final class FileNameExtensionFilter extends FileFilter {
    // Description of this filter.
    private final String description;
    // Known extensions.
    private final String[] extensions;
    // Cached ext
    private final String[] lowerCaseExtensions;

    /**
     * Creates a {@code FileNameExtensionFilter} with the specified
     * description and file name extensions. The returned {@code
     * FileNameExtensionFilter} will accept all directories and any
     * file with a file name extension contained in {@code extensions}.
     *
     * @param description textual description for the filter, may be
     *                    {@code null}
     * @param extensions the accepted file name extensions
     * @throws IllegalArgumentException if extensions is {@code null}, empty,
     *         contains {@code null}, or contains an empty string
     * @see #accept
     */
    public FileNameExtensionFilter(String description, String... extensions) {
        if (extensions == null || extensions.length == 0) {
            throw new IllegalArgumentException(
                    "Extensions must be non-null and not empty");
        }
        this.description = description;
        this.extensions = new String[extensions.length];
        this.lowerCaseExtensions = new String[extensions.length];
        for (int i = 0; i < extensions.length; i++) {
            if (extensions[i] == null || extensions[i].length() == 0) {
                throw new IllegalArgumentException(
                    "Each extension must be non-null and not empty");
            }
            this.extensions[i] = extensions[i];
            lowerCaseExtensions[i] = extensions[i].toLowerCase(Locale.ENGLISH);
        }
    }

    /**
     * Tests the specified file, returning true if the file is
     * accepted, false otherwise. True is returned if the extension
     * matches one of the file name extensions of this {@code
     * FileFilter}, or the file is a directory.
     *
     * @param f the {@code File} to test
     * @return true if the file is to be accepted, false otherwise
     */
    public boolean accept(File f) {
        if (f != null) {
            if (f.isDirectory()) {
                return true;
            }
            // NOTE: we tested implementations using Maps, binary search
            // on a sorted list and this implementation. All implementations
            // provided roughly the same speed, most likely because of
            // overhead associated with java.io.File. Therefor we've stuck
            // with the simple lightweight approach.
            String fileName = f.getName();
            int i = fileName.lastIndexOf('.');
            if (i > 0 && i < fileName.length() - 1) {
                String desiredExtension = fileName.substring(i+1).
                        toLowerCase(Locale.ENGLISH);
                for (String extension : lowerCaseExtensions) {
                    if (desiredExtension.equals(extension)) {
                        return true;
                    }
                }
            }
        }
        return false;
    }

    /**
     * The description of this filter. For example: "JPG and GIF Images."
     *
     * @return the description of this filter
     */
    public String getDescription() {
        return description;
    }

    /**
     * Returns the set of file name extensions files are tested against.
     *
     * @return the set of file name extensions files are tested against
     */
    public String[] getExtensions() {
        String[] result = new String[extensions.length];

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