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 * Copyright (c) 2003, 2017, 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
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 */

package java.lang;

import java.io.IOException;
import java.nio.CharBuffer;
import java.util.Objects;

/**
 * A {@code Readable} is a source of characters. Characters from
 * a {@code Readable} are made available to callers of the read
 * method via a {@link java.nio.CharBuffer CharBuffer}.
 *
 * @since 1.5
 */
public interface Readable {

    /**
     * Attempts to read characters into the specified character buffer.
     * The buffer is used as a repository of characters as-is: the only
     * changes made are the results of a put operation. No flipping or
     * rewinding of the buffer is performed.
     *
     * @param cb the buffer to read characters into
     * @return The number of {@code char} values added to the buffer,
     *                 or -1 if this source of characters is at its end
     * @throws IOException if an I/O error occurs
     * @throws NullPointerException if cb is null
     * @throws java.nio.ReadOnlyBufferException if cb is a read only buffer
     */
    public int read(java.nio.CharBuffer cb) throws IOException;

    /**
     * Reads all characters from this source and appends them to a destination
     * in the order in which they are read. On return, the source of characters
     * will be at its end.
     * <p>
     * This method may block indefinitely while reading from the source or
     * writing to the destination. If the source or destination is
     * {@link AutoCloseable closeable}, then the behavior when either is
     * <i>asynchronously closed</i>, or the thread is interrupted during the
     * transfer, is highly implementation-dependent and hence unspecified.
     * <p>
     * If an I/O error occurs during the operation, then not all characters
     * might have been transferred and the source or destination could be
     * left in an inconsistent state. The caller of this method should therefore
     * ensure in such a case that measures are taken to release any resources
     * held by the source and destination.
     *
     * @implSpec
     * The default implementation invokes the read method to read all characters
     * from this source and invokes the {@link Appendable#append(CharSequence, int, int)}
     * method to write all characters to the appendable.
     * The total amount will be added up by after the write method has been
     * completed.
     *
     * The default implementation behaves as if:
     * <pre>{@code
     *     long transferred = 0;
     *     CharBuffer buffer = CharBuffer.allocate(8192);
     *     int read;
     *     while ((read = this.read(buffer)) >= 0) {
     *         buffer.rewind();
     *         out.append(buffer, 0, read);
     *         transferred += read;
     *     }
     *     return transferred;
     * }</pre>
     *
     * @implNote
     * The default implementation should usually be overridden in cases where
     * the implementer is already a {@link CharSequence} or its data is already
     * available in the internal representation in order not having the extra
     * overhead creating a buffer in order to transfer its data to the
     * destination.
     *
     * @param  out the appendable, non-null
     * @return the number of characters transferred
     * @throws IOException if an I/O error occurs when reading or writing
     * @throws NullPointerException if {@code out} is {@code null}
     *
     * @since 10
     */
    public default long transferTo(Appendable out) throws IOException {
        Objects.requireNonNull(out, "out");
        long transferred = 0;
        CharBuffer buffer = CharBuffer.allocate(8192);
        int read;
        while ((read = this.read(buffer)) >= 0) {
            buffer.rewind();
            out.append(buffer, 0, read);
            transferred += read;
        }
        return transferred;
    }
}