DirectCharBufferRU.java

/*
 * Copyright (c) 2000, 2018, 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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 * questions.
 */

package java.nio;

import sun.nio.ch.DirectBuffer;

// 只读、直接缓冲区，是DirectCharBufferU的只读版本
class DirectCharBufferRU extends DirectCharBufferU implements DirectBuffer {
    
    /*▼ 构造器 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    // For duplicates and slices
    DirectCharBufferRU(DirectBuffer db, int mark, int pos, int lim, int cap, int off) {
        super(db, mark, pos, lim, cap, off);
        this.isReadOnly = true;
    }
    
    /*▲ 构造器 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 只读/直接 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    // 只读/可读写
    public boolean isReadOnly() {
        return true;
    }
    
    // 直接缓冲区/非直接缓冲区
    public boolean isDirect() {
        return true;
    }
    
    /*▲ 只读/直接 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 创建新缓冲区，新旧缓冲区共享内部的存储容器 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    // 切片，截取旧缓冲区的【活跃区域】，作为新缓冲区的【原始区域】。两个缓冲区标记独立。
    public CharBuffer slice() {
        int pos = this.position();
        int lim = this.limit();
        assert (pos <= lim);
        int rem = (pos <= lim ? lim - pos : 0);
        int off = (pos << 1);
        assert (off >= 0);
        return new DirectCharBufferRU(this, -1, 0, rem, rem, off);
    }
    
    // 副本，新缓冲区共享旧缓冲区的【原始区域】，且新旧缓冲区【活跃区域】一致。两个缓冲区标记独立。
    public CharBuffer duplicate() {
        return new DirectCharBufferRU(this, this.markValue(), this.position(), this.limit(), this.capacity(), 0);
    }
    
    // 只读副本，新缓冲区共享旧缓冲区的【原始区域】，且新旧缓冲区【活跃区域】一致。两个缓冲区标记独立。
    public CharBuffer asReadOnlyBuffer() {
        return duplicate();
    }
    
    // 子副本，新缓冲区的【活跃区域】取自旧缓冲区【活跃区域】的[start，end)部分
    public CharBuffer subSequence(int start, int end) {
        int pos = position();
        int lim = limit();
        assert (pos <= lim);
        pos = (pos <= lim ? pos : lim);
        int len = lim - pos;
        
        if((start < 0) || (end > len) || (start > end))
            throw new IndexOutOfBoundsException();
        return new DirectCharBufferRU(this, -1, pos + start, pos + end, capacity(), offset);
    }
    
    /*▲ 创建新缓冲区，新旧缓冲区共享内部的存储容器 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 只读缓冲区，禁止写入 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    // 向position处写入char，并将position递增
    public CharBuffer put(char x) {
        throw new ReadOnlyBufferException();
    }
    
    // 向i处写入char
    public CharBuffer put(int i, char x) {
        throw new ReadOnlyBufferException();
    }
    
    // 将源缓冲区src的内容全部写入到当前缓冲区
    public CharBuffer put(CharBuffer src) {
        throw new ReadOnlyBufferException();
    }
    
    // 从源字符数组src的offset处开始，复制length个元素，写入到当前缓冲区【活跃区域】内（考虑偏移量）
    public CharBuffer put(char[] src, int offset, int length) {
        throw new ReadOnlyBufferException();
    }
    
    /*▲ 只读缓冲区，禁止写入 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 禁止压缩，因为禁止写入，压缩没意义 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    // 压缩缓冲区，将当前未读完的数据挪到容器起始处，可用于读模式到写模式的切换，但又不丢失之前读入的数据。
    public CharBuffer compact() {
        throw new ReadOnlyBufferException();
    }
    
    /*▲ 禁止压缩，因为禁止写入，压缩没意义 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 字节顺序 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    // 返回与平台字节顺序相同的字节序
    public ByteOrder order() {
        return ((ByteOrder.nativeOrder() != ByteOrder.BIG_ENDIAN) ? ByteOrder.LITTLE_ENDIAN : ByteOrder.BIG_ENDIAN);
    }
    
    // 返回‘char’的字节序（此类中与平台字节序相同）
    ByteOrder charRegionOrder() {
        return order();
    }
    
    /*▲ 字节顺序 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    
    // 返回内部存储结构的引用（一般用于非直接缓存区）
    @Override
    Object base() {
        return null;
    }
    
    // 构造新的子串
    public String toString(int start, int end) {
        if((end>limit()) || (start>end)) {
            throw new IndexOutOfBoundsException();
        }
    
        try {
            int len = end - start;
            char[] ca = new char[len];
            CharBuffer cb = CharBuffer.wrap(ca);
            CharBuffer db = this.duplicate();
            db.position(start);
            db.limit(end);
            cb.put(db);
            return new String(ca);
        } catch(StringIndexOutOfBoundsException x) {
            throw new IndexOutOfBoundsException();
        }
    }
}