Package java.io | Java In A Nutshell, 5th Edition

Package java.io

Java 1.0

The java.io package is large, but most of the classes it contains fall into a well-structured hierarchy. Most of the package consists of byte streamssubclasses of InputStream or OutputStream and character streamssubclasses of Reader or Writer . Each of these stream subtypes has a specific purpose, and, despite its size , java.io is a straightforward package to understand and to use. In Java 1.4, the java.io package was complemented by a "New I/O API" defined in the java.nio package and its subpackages. The java.nio package is totally new, although it included some compatibility with the classes in this package. It was designed for high-performance I/O, particularly for use in servers and has a lower-level API than this package does. The I/O facilities of java.io are still quite adequate for most of the I/O required by typical client-side applications.

Before we consider the stream classes that comprise the bulk of this package, let's examine the important nonstream classes. File represents a file or directory name in a system-independent way and provides methods for listing directories, querying file attributes, and renaming and deleting files. FilenameFilter is an interface that defines a method that accepts or rejects specified filenames. It is used by File to specify what types of files should be included in directory listings. RandomAccessFile allows you to read from or write to arbitrary locations of a file. Often, though, you'll prefer sequential access to a file and should use one of the stream classes.

InputStream and OutputStream are abstract classes that define methods for reading and writing bytes. Their subclasses allow bytes to be read from and written to a variety of sources and sinks. FileInputStream and FileOutputStream read from and write to files. ByteArrayInputStream and ByteArrayOutputStream read from and write to an array of bytes in memory. PipedInputStream reads bytes from a PipedOutputStream , and PipedOutputStream writes bytes to a PipedInputStream . These classes work together to implement a pipe for communication between threads.

FilterInputStream and FilterOutputStream are special; they filter input and output bytes. When you create a FilterInputStream , you specify an InputStream for it to filter. When you call the read( ) method of a FilterInputStream , it calls the read( ) method of its InputStream , processes the bytes it reads, and returns the filtered bytes. Similarly, when you create a FilterOutputStream , you specify an OutputStream to be filtered. Calling the write( ) method of a FilterOutputStream causes it to process your bytes in some way and then pass those filtered bytes to the write( ) method of its OutputStream .

FilterInputStream and FilterOutputStream do not perform any filtering themselves ; this is done by their subclasses. BufferedInputStream and BufferedOutputStream are filtered streams that provide input and output buffering and can increase I/O efficiency. DataInputStream reads raw bytes from a stream and interprets them in various binary formats. It has various methods to read primitive Java data types in their standard binary formats. DataOutputStream allows you to write Java primitive data types in binary format. The ObjectInputStream and ObjectOutputStream classes are special. These byte-stream classes are used for serializing and deserializing the internal state of objects for storage or interprocess communication.

The byte streams just described are complemented by an analogous set of character input and output streams. Reader is the superclass of all character input streams, and Writer is the superclass of all character output streams. Most of the Reader and Writer streams have obvious byte-stream analogs. BufferedReader is a commonly used stream; it provides buffering for efficiency and also has a readLine( ) method to read a line of text at a time. PrintWriter is another very common stream; its methods allow output of a textual representation of any primitive Java type or of any object (via the object's toString( ) method).

Java 5.0 adds the Closeable and Flushable interfaces to identify types that have close( ) and flush( ) methods. All streams have a close( ) method and implement the Closeable interface. And all byte and character output streams have a flush( ) method and implement Flushable . In a related change, all character output streams (and the byte stream PrintStream ) implement the (new in Java 5.0) interface java.lang.Appendable , making them suitable for use with the java.util.Formatter class. Similarly, all character input streams implement the java.lang.Readable interface, making them suitable for use with the java.util.Scanner class. Finally, both PrintStream and PrintWriter have been enhanced in two ways for Java 5.0. Both now include constructors for creating a stream that writes directly to a file. And both include formatted-text output methods printf( ) and format( ) . See java.util.Formatter for details.

Interfaces

 public interface  Closeable  ; public interface  DataInput  ; public interface  DataOutput  ; public interface  Externalizable  extends Serializable; public interface  FileFilter  ; public interface  FilenameFilter  ; public interface  Flushable  ; public interface  ObjectInput  extends DataInput; public interface  ObjectInputValidation  ; public interface  ObjectOutput  extends DataOutput; public interface  ObjectStreamConstants  ; public interface  Serializable  ;

Classes

 public class  File  implements Serializable, Comparable<File>; public final class  FileDescriptor  ; public final class  FilePermission  extends java.security.Permission implements     Serializable; public abstract class  InputStream  implements Closeable;    public class  ByteArrayInputStream  extends InputStream;    public class  FileInputStream  extends InputStream;    public class  FilterInputStream  extends InputStream;       public class  BufferedInputStream  extends FilterInputStream;       public class  DataInputStream  extends FilterInputStream implements        DataInput;       public class  LineNumberInputStream  extends FilterInputStream;       public class  PushbackInputStream  extends FilterInputStream;    public class  ObjectInputStream  extends InputStream implements ObjectInput,        ObjectStreamConstants;    public class  PipedInputStream  extends InputStream;    public class  SequenceInputStream  extends InputStream;    public class  StringBufferInputStream  extends InputStream; public abstract static class  ObjectInputStream.GetField  ; public abstract static class  ObjectOutputStream.PutField  ; public class  ObjectStreamClass  implements Serializable; public class  ObjectStreamField  implements Comparable<Object>; public abstract class  OutputStream  implements Closeable, Flushable;    public class  ByteArrayOutputStream  extends OutputStream;    public class  FileOutputStream  extends OutputStream;    public class  FilterOutputStream  extends OutputStream;       public class  BufferedOutputStream  extends FilterOutputStream;       public class  DataOutputStream  extends FilterOutputStream implements        DataOutput;       public class  PrintStream  extends FilterOutputStream implements Appendable,        Closeable;    public class  ObjectOutputStream  extends OutputStream implements ObjectOutput,        ObjectStreamConstants;    public class  PipedOutputStream  extends OutputStream; public class  RandomAccessFile  implements Closeable, DataInput, DataOutput; public abstract class  Reader  implements Closeable, Readable;    public class  BufferedReader  extends Reader;       public class  LineNumberReader  extends BufferedReader;    public class  CharArrayReader  extends Reader;    public abstract class  FilterReader  extends Reader;       public class  PushbackReader  extends FilterReader;    public class  InputStreamReader  extends Reader;       public class  FileReader  extends InputStreamReader;    public class  PipedReader  extends Reader;    public class  StringReader  extends Reader; public final class  SerializablePermission  extends java.security.BasicPermission; public class  StreamTokenizer  ; public abstract class  Writer  implements Appendable, Closeable, Flushable;    public class  BufferedWriter  extends Writer;    public class  CharArrayWriter  extends Writer;    public abstract class  FilterWriter  extends Writer;    public class  OutputStreamWriter  extends Writer;       public class  FileWriter  extends OutputStreamWriter;    public class  PipedWriter  extends Writer;    public class  PrintWriter  extends Writer;    public class  StringWriter  extends Writer;

Exceptions

 public class  IOException  extends Exception;    public class  CharConversionException  extends IOException;    public class  EOFException  extends IOException;    public class  FileNotFoundException  extends IOException;    public class  InterruptedIOException  extends IOException;    public abstract class  ObjectStreamException  extends IOException;       public class  InvalidClassException  extends ObjectStreamException;       public class  InvalidObjectException  extends ObjectStreamException;       public class  NotActiveException  extends ObjectStreamException;       public class  NotSerializableException  extends ObjectStreamException;       public class  OptionalDataException  extends ObjectStreamException;       public class  StreamCorruptedException  extends ObjectStreamException;       public class  WriteAbortedException  extends ObjectStreamException;    public class  SyncFailedException  extends IOException;    public class  UnsupportedEncodingException  extends IOException;    public class  UTFDataFormatException  extends IOException;