Java I/O

Writing Files

The java.io.FileOutputStream class is a concrete subclass of java.io.OutputStream that provides output streams connected to files.

public class FileOutputStream extends OutputStream

This class has all the usual methods of output streams, such as write(), flush(), and close(), which are used exactly as they are for any other output stream.

public native void write(int b) throws IOException
public void write(byte[] data) throws IOException
public void write(byte[] data, int offset, int length) throws IOException
public native void close() throws IOException

These are all implemented in native code except for the two multibyte write() methods. These, however, just pass their arguments on to a private native method called writeBytes(), so effectively all these methods are implemented with native code.

There are three main FileOutputStream() constructors, differing primarily in how the file is specified:

public FileOutputStream(String filename) throws IOException
public FileOutputStream(File file) throws IOException
public FileOutputStream(FileDescriptor fd)

The first constructor uses a string containing the name of the file; the second constructor uses a java.io.File object; the third constructor uses a java.io.FileDescriptor object. I will avoid using the second and third constructors until I’ve discussed File objects and file descriptors (Chapter 12). To write data to a file, just pass the name of the file to the FileOutputStream() constructor, then use the write() methods ...