1 Chapter 10: Writing Files

2 Basic Information You can regard the file as a series of bytes with no specific information about its structure Common file extension give us some clues about the file internal structure Two Modes of accessing file: –Sequential access –Random access

3 Why: They are very efficient, because they use OS buffers A file channel object defines a channel for a physical file You can create a file channel object using “fileOutputStream.getChannel()” All the channel related classes and interfaces are found in java.nio.channels File Channels

4 File Channels (Cont.) Your program Buffer Object File Stream Object Channel Object

5 Almost all classes inherit from the Buffer class. They are found in java.nio ByteBuffer is the only one used in I/O Viewer Buffers as CharBuffer, Double, etc. Buffer capacity, position, and limit {capacity(), position(), limit(), remaining(), hasRemaining()} Buff.limit(512).position(256) ByteBuffer buff = ByteBuffer.allocate(1024); IntBuffer intBuf = buf.asIntBuffer(); ByteBuffer buf = ByteBuffer.wrap(str.getBytes()); Relative put/get and absolute put/get The Buffer Class

6 Putting data relatively in a view buffer only update the position of the view buffer NOT the backing buffer Write data to a file both position and limit should be set properly buf.limit(but.position()).position(0) = buf.flip(); Ex: WriteAString.java WriteAStringAsBytes.java WriteProverbs.java PrimesToFile.java & PrimeToFile2.java The Buffer Class (Cont)