Untitled Quiz

Object-Oriented Programming: Streams and Files

• Data Streams: Data is stored as a sequence of bytes. Higher-level structures like characters or objects can be considered sequences of bytes.
• Streams: A sequence of data read from or written to a destination.
  • Source: Memory, keyboard, file.
  • Destination: Memory, screen, file.
• Java programs use objects of different stream types to send and receive data.
• Streams can be connected to various sources (floppy, hard disk, network, memory). The implementation abstracts away specific connections, focusing only on performing input/output (I/O) operations.
• Types of Streams:
  • Byte streams: Manipulate data in bytes.
    • InputStream: Abstract base class for reading byte streams.
    • OutputStream: Abstract base class for writing byte streams.
  • Character streams: Manipulate data as Unicode text.
    • Reader: Abstract base class for reading character streams.
    • Writer: Abstract base class for writing character streams.

Stream Hierarchies

• InputStream Hierarchy: Shows subclasses of InputStream, like FileInputStream, PipedInputStream, DataInputStream, etc.
• OutputStream Hierarchy: Shows subclasses of OutputStream, like FileOutputStream, PipedOutputStream, DataOutputStream, etc.
• Reader Hierarchy: Shows subclasses of Reader, like BufferedReader, FileReader, InputStreamReader, etc.
• Writer Hierarchy: Shows subclasses of Writer, like BufferedWriter, FileWriter, OutputStreamWriter, etc.

Methods of InputStream

• int read(): Reads the next byte of data from the input stream.
• int read(byte[] b): Reads b.length bytes from the input stream to the byte array b.
• int read(byte[] b, int offset, int length): Reads length bytes from the input stream to the byte array b starting at offset.
• void close(): Closes the input stream.

Methods of OutputStream

• int write(int c): Writes the single byte c to the output stream.
• int write(byte[] b): Writes b.length bytes from the byte array b to the output stream.
• int write(byte[] b, int offset, int length): Writes length bytes from the byte array b, starting from offset, to the output stream.
• void close(): Closes the output stream.
• void flush(): Flushes the data from the buffer to the output stream.

Methods of Reader

• int read(): Reads the next character from the input stream.
• int read(char[] cbuf): Reads cbuf.length characters from the input stream to the char array cbuf.
• int read(char[] cbuf, int off, int len): Reads len characters from the input stream to the char array cbuf, starting at offset off.
• void close(): Closes the input stream.

Methods of Writer

• int write(int c): Writes the single character c to the output stream.
• int write(char[] cbuf): Writes cbuf.length characters from the char array cbuf to the output stream.
• int write(char[] cbuf, int off, int len): Writes len characters from the char array cbuf, starting at offset off, to the stream.
• void close(): Closes the output stream.
• void flush(): Flushes the data stream from the buffer to the output stream.

Important Stream Types

• InputStream/OutputStream: Base classes with few features.
• FileInputStream/FileOutputStream: Specifically for connecting to files.
• BufferedInputStream/BufferedOutputStream: Improve I/O performance by adding buffers.
• BufferedReader/BufferedWriter: Convert bytes to Unicode characters and strings.

Input/Output Stream Object

• To read/write data, a stream object is needed.
• The I/O stream object is attached to a data source or destination.
• Example: BufferedReader in = new BufferedReader(new FileReader(filename));

Use of Buffered Streams

• Buffering improves I/O performance by reading/writing data in blocks.
• Reduces the number of accesses to I/O devices.
• Data is written to a buffer, and when it fills, it's transferred to the destination.
• The flush() method forces data to be written to destination.
• Data is read from the buffer when it's not empty.

Standard I/O Streams

• Java.lang package includes System.out and System.err (PrintStream).
  • These can be used directly to print to the standard output and error streams.
• System.in is an InputStream object, used with InputStreamReader and BufferedReader.

The File Class

• In java.io package, provides basic file and directory operations.
• Files are not streams; they represent a file structure.
• Create/open files.
• Query directory information.

Create a File Object

• File myFile = new File("data.txt"); or File myFile = new File("myDocs", "data.txt");
• Directories are treated the same as files. Example: File myDir = new File("myDocs");

File's Methods

• File/directory name: getName(), getPath(), getAbsolutePath(), getParent(), renameTo(File newName)
• File/directory status: exists(), canWrite(), canRead(), isFile(), isDirectory()
• Status: lastModified(), length(), delete()
• Directory: mkdir(), list()

Manipulate Text Files

• Read: FileReader (for individual characters), BufferedReader(for reading lines).
• Write: FileWriter (for individual characters), PrintWriter (for writing lines).

Read from a Text File

• Uses a BufferedReader, typically linked to a FileReader, to read lines from a file until the end of the file.
• The readLine() method is used to read lines from the file, and the returned string is printed to the console.

Write to a Text File

• Uses a PrintWriter, typically linked to FileWriter, to write lines into the file.
• out.write() is used to write formatted data or strings into the file.

Manipulate Binary Files

• Read: FileInputStream, DataInputStream, ObjectInputStream
• Write: FileOutputStream, DataOutputStream, ObjectOutputStream

DataInputStream/DataOutputStream

• DataInputStream: Reads primitive data types. -Methods include readBoolean, readByte, readChar, readShort, readInt, readLong, readFloat, readDouble.
• DataOutputStream: Writes primitive data types.
  • Methods include writeBoolean, writeByte, writeChar, writeShort, writeInt, writeLong, writeFloat, writeDouble

Write Primitive Data

• Code example showing how to write primitive data to a binary file using FileOutputStream and DataOutputStream.

Read Primitive Data

• Code example showing how to read primitive data from a binary file using FileInputStream and DataInputStream.

File of Objects

• Objects can be stored in files by using serialization.
• Data classes must implement the Serializable interface to be serialized.

Write Object

• The code to write an object to a file, using serialization with ObjectOutputStream and FileOutputStream.

Read Objects

• The code to read an object from a file using deserialization with ObjectInputStream and FileInputStream.

RandomAccessFile Class

• Implements DataInput and DataOutput interfaces.
• Enables random access to data within a file.
• Allows reading and writing data at specific byte offsets.

Write with RandomAccessFile

• Code example for writing to a file using RandomAccessFile.

Read with RandomAccessFile

• Code example for reading from a file using RandomAccessFile.