Class MappedByteBuffer

A return value of true implies that it is highly likely that all of the data in this buffer is resident in physical memory and may therefore be accessed without incurring any virtual-memory page faults or I/O operations. A return value of false does not necessarily imply that the buffer's content is not resident in physical memory.

The returned value is a hint, rather than a guarantee, because the underlying operating system may have paged out some of the buffer's data by the time that an invocation of this method returns.

This method makes a best effort to ensure that, when it returns, this buffer's content is resident in physical memory. Invoking this method may cause some number of page faults and I/O operations to occur.

If the file mapped into this buffer resides on a local storage device then when this method returns it is guaranteed that all changes made to the buffer since it was created, or since this method was last invoked, will have been written to that device.

If the file does not reside on a local device then no such guarantee is made.

If this buffer was not mapped in read/write mode (FileChannel.MapMode.READ_WRITE) then invoking this method may have no effect. In particular, the method has no effect for buffers mapped in read-only or private mapping modes. This method may or may not have an effect for implementation-specific mapping modes.

If the file mapped into this buffer resides on a local storage device then when this method returns it is guaranteed that all changes made to the selected region buffer since it was created, or since this method was last invoked, will have been written to that device. The force operation is free to write bytes that lie outside the specified region, for example to ensure that data blocks of some device-specific granularity are transferred in their entirety.

If the file does not reside on a local device then no such guarantee is made.

If this buffer was not mapped in read/write mode (FileChannel.MapMode.READ_WRITE) then invoking this method may have no effect. In particular, the method has no effect for buffers mapped in read-only or private mapping modes. This method may or may not have an effect for implementation-specific mapping modes.

Invoking this method neither changes nor discards the mark's value.

Invoke this method before using a sequence of channel-read or put operations to fill this buffer. For example:

    buf.clear();     // Prepare buffer for reading
    in.read(buf);    // Read data

This method does not actually erase the data in the buffer, but it is named as if it did because it will most often be used in situations in which that might as well be the case.

After a sequence of channel-read or put operations, invoke this method to prepare for a sequence of channel-write or relative get operations. For example:

    buf.put(magic);    // Prepend header
    in.read(buf);      // Read data into rest of buffer
    buf.flip();        // Flip buffer
    out.write(buf);    // Write header + data to channel

This method is often used in conjunction with the compact method when transferring data from one place to another.

Invoke this method before a sequence of channel-write or get operations, assuming that the limit has already been set appropriately. For example:

    out.write(buf);    // Write remaining data
    buf.rewind();      // Rewind buffer
    buf.get(array);    // Copy data into array

The content of the new buffer will start at this buffer's current position. Changes to this buffer's content will be visible in the new buffer, and vice versa; the two buffers' position, limit, and mark values will be independent.

The new buffer's position will be zero, its capacity and its limit will be the number of bytes remaining in this buffer, its mark will be undefined, and its byte order will be BIG_ENDIAN. The new buffer will be direct if, and only if, this buffer is direct, and it will be read-only if, and only if, this buffer is read-only.

Reading bytes into physical memory by invoking load() on the returned buffer, or writing bytes to the storage device by invoking force() on the returned buffer, will only act on the sub-range of this buffer that the returned buffer represents, namely [position(),limit()).

The content of the new buffer will start at position index in this buffer, and will contain length elements. Changes to this buffer's content will be visible in the new buffer, and vice versa; the two buffers' position, limit, and mark values will be independent.

The new buffer's position will be zero, its capacity and its limit will be length, its mark will be undefined, and its byte order will be BIG_ENDIAN. The new buffer will be direct if, and only if, this buffer is direct, and it will be read-only if, and only if, this buffer is read-only.

Reading bytes into physical memory by invoking load() on the returned buffer, or writing bytes to the storage device by invoking force() on the returned buffer, will only act on the sub-range of this buffer that the returned buffer represents, namely [index,index+length), where index and length are assumed to satisfy the preconditions.

The content of the new buffer will be that of this buffer. Changes to this buffer's content will be visible in the new buffer, and vice versa; the two buffers' position, limit, and mark values will be independent.

The new buffer's capacity, limit, position, and mark values will be identical to those of this buffer, and its byte order will be BIG_ENDIAN. The new buffer will be direct if, and only if, this buffer is direct, and it will be read-only if, and only if, this buffer is read-only.

The bytes between the buffer's current position and its limit, if any, are copied to the beginning of the buffer. That is, the byte at index p = position() is copied to index zero, the byte at index p + 1 is copied to index one, and so forth until the byte at index limit() - 1 is copied to index n = limit() - 1 - p. The buffer's position is then set to n+1 and its limit is set to its capacity. The mark, if defined, is discarded.

The buffer's position is set to the number of bytes copied, rather than to zero, so that an invocation of this method can be followed immediately by an invocation of another relative put method.

Invoke this method after writing data from a buffer in case the write was incomplete. The following loop, for example, copies bytes from one channel to another via the buffer buf:

    buf.clear();          // Prepare buffer for use
    while (in.read(buf) >= 0 || buf.position != 0) {
        buf.flip();
        out.write(buf);
        buf.compact();    // In case of partial write
    }