### Question:
JimfsFileChannel extends FileChannel { @Override public int write(ByteBuffer src) throws IOException { checkNotNull(src); checkOpen(); checkWritable(); int written = 0; synchronized (this) { boolean completed = false; try { if (!beginBlocking()) { return 0; } file.writeLock().lockInterruptibly(); try { if (append) { position = file.size(); } written = file.write(position, src); position += written; file.updateModifiedTime(); completed = true; } finally { file.writeLock().unlock(); } } catch (InterruptedException e) { Thread.currentThread().interrupt(); } finally { endBlocking(completed); } } return written; } JimfsFileChannel(
      RegularFile file, Set<OpenOption> options, FileSystemState fileSystemState); AsynchronousFileChannel asAsynchronousFileChannel(ExecutorService executor); @Override int read(ByteBuffer dst); @Override long read(ByteBuffer[] dsts, int offset, int length); @Override int read(ByteBuffer dst, long position); @Override int write(ByteBuffer src); @Override long write(ByteBuffer[] srcs, int offset, int length); @Override int write(ByteBuffer src, long position); @Override long position(); @Override FileChannel position(long newPosition); @Override long size(); @Override FileChannel truncate(long size); @Override void force(boolean metaData); @Override long transferTo(long position, long count, WritableByteChannel target); @Override long transferFrom(ReadableByteChannel src, long position, long count); @Override MappedByteBuffer map(MapMode mode, long position, long size); @Override FileLock lock(long position, long size, boolean shared); @Override FileLock tryLock(long position, long size, boolean shared);  }### Answer:
@Test public void testWrite() throws IOException { RegularFile file = regularFile(0); FileChannel channel = channel(file, WRITE); assertEquals(0, channel.position()); ByteBuffer buf = buffer("1234567890"); ByteBuffer buf2 = buffer("1234567890"); assertEquals(10, channel.write(buf)); assertEquals(10, channel.position()); buf.flip(); assertEquals(20, channel.write(new ByteBuffer[] {buf, buf2})); assertEquals(30, channel.position()); buf.flip(); buf2.flip(); assertEquals(20, channel.write(new ByteBuffer[] {buf, buf2}, 0, 2)); assertEquals(50, channel.position()); buf.flip(); assertEquals(10, channel.write(buf, 5)); assertEquals(50, channel.position()); }
@Test public void testWriteNegative() throws IOException { FileChannel channel = channel(regularFile(0), READ, WRITE); try { channel.write(buffer("111"), -1); fail(); } catch (IllegalArgumentException expected) { } ByteBuffer[] bufs = {buffer("111"), buffer("111")}; try { channel.write(bufs, -1, 10); fail(); } catch (IndexOutOfBoundsException expected) { } try { channel.write(bufs, 0, -1); fail(); } catch (IndexOutOfBoundsException expected) { } }