HeapLongBufferR.java

/*
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 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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 * This code is free software; you can redistribute it and/or modify it
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 * 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.nio;

/**
 * A read-only HeapLongBuffer.  This class extends the corresponding
 * read/write class, overriding the mutation methods to throw a {@link
 * ReadOnlyBufferException} and overriding the view-buffer methods to return an
 * instance of this class rather than of the superclass.
 */
// 只读、非直接缓冲区，是HeapLongBuffer的只读版本，禁止写入操作，内部存储结构实现为long[]
class HeapLongBufferR extends HeapLongBuffer {
    
    // Cached array base offset
    private static final long ARRAY_BASE_OFFSET = UNSAFE.arrayBaseOffset(long[].class);
    // Cached array base offset
    private static final long ARRAY_INDEX_SCALE = UNSAFE.arrayIndexScale(long[].class);
    
    
    /*▼ 构造器 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    protected HeapLongBufferR(long[] buf, int mark, int pos, int lim, int cap, int off) {
        super(buf, mark, pos, lim, cap, off);
        this.isReadOnly = true;
    }
    
    HeapLongBufferR(int cap, int lim) {            // package-private
        super(cap, lim);
        this.isReadOnly = true;
    }
    
    HeapLongBufferR(long[] buf, int off, int len) { // package-private
        super(buf, off, len);
        this.isReadOnly = true;
    }
    
    /*▲ 构造器 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 只读/非直接 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    // 只读/可读写
    public boolean isReadOnly() {
        return true;
    }
    
    /*▲ 只读/非直接 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    /*▼ 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 LongBuffer slice() {
        return new HeapLongBufferR(hb, -1, 0, this.remaining(), this.remaining(), this.position() + offset);
    }
    
    // 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 LongBuffer duplicate() {
        return new HeapLongBufferR(hb, this.markValue(), this.position(), this.limit(), this.capacity(), offset);
    }
    
    // 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 LongBuffer asReadOnlyBuffer() {
        return duplicate();
    }
    
    /*▲ 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，禁止写入操作 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    // 向position处（可能需要加offset）写入long，并将position递增
    public LongBuffer put(long x) {
        throw new ReadOnlyBufferException();
    }
    
    // 向i处（可能需要加offset）写入long
    public LongBuffer put(int i, long x) {
        throw new ReadOnlyBufferException();
    }
    
    // 从源long数组src的offset处开始，复制length个元素，写入到当前缓冲区
    public LongBuffer put(long[] src, int offset, int length) {
        throw new ReadOnlyBufferException();
    }
    
    // 将源缓冲区src的内容全部写入到当前缓冲区
    public LongBuffer put(LongBuffer src) {
        throw new ReadOnlyBufferException();
    }
    
    /*▲ 只读缓冲区，禁止写入操作 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 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 LongBuffer compact() {
        throw new ReadOnlyBufferException();
    }
    
    /*▲ 禁止压缩，因为禁止写入，压缩没意义 ████████████████████████████████████████████████████████████████████████████████┛ */
    
    
    
    /*▼ 字节顺序 ████████████████████████████████████████████████████████████████████████████████┓ */
    
    // 返回该缓冲区的字节序（大端还是小端）
    public ByteOrder order() {
        return ByteOrder.nativeOrder();
    }
    
    /*▲ 字节顺序 ████████████████████████████████████████████████████████████████████████████████┛ */
}