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IO streams

Created on Dec 4, ’22 ・ Last update on Mar 7, ’23

Summary of the Java I/O tutorial.

Java I/O Streams

Byte streams

  • InputStream (implements Closeable)
    • ByteArrayInputStream
    • FileInputStream
    • FilterInputStream
      • BufferedInputStream
      • DataInputStream (implements DataInput)
      • LineNumberInputStream
      • PushbackInputStream
    • ObjectInputStream (implements ObjectInput, ObjectStreamConstants)
    • PipedInputStream
    • SequenceInputStream
    • StringBufferInputStream
  • OutputStream (implements Closeable, Flushable)
    • ByteArrayOutputStream
    • FileOutputStream
    • FilterOutputStream
      • BufferedOutputStream
      • DataOutputStream (implements DataOutput)
      • PrintStream (implements java.lang.Appendable, Closeable)
    • ObjectOutputStream (implements ObjectOutput, ObjectStreamConstants)
    • PipedOutputStream

All byte stream classes are descended from the abstract InputStream and OutputStream classes. All other stream types are built on byte streams.

Use: a FileOutputStream wrapped in a BufferedOutputStream. Same for an input stream.

Character streams

  • Reader (implements Closeable, java.lang.Readable)
    • BufferedReader
      • LineNumberReader
    • CharArrayReader
    • FilterReader
      • PushbackReader
    • InputStreamReader
      • FileReader
    • PipedReader
    • StringReader
  • Writer (implements java.lang.Appendable, Closeable, Flushable)
    • BufferedWriter
    • CharArrayWriter
    • FilterWriter
    • OutputStreamWriter
      • FileWriter
    • PipedWriter
    • PrintWriter
    • StringWriter

All character stream classes are descended from the abstract Reader and Writer.

On FileReader vs FileInputStream:

Notice that both CopyBytes and CopyCharacters use an int variable to read to and write from. However, in CopyCharacters, the int variable holds a character value in its last 16 bits; in CopyBytes, the int variable holds a byte value in its last 8 bits.

Character streams are often "wrappers" for byte streams. The character stream uses the byte stream to perform the physical I/O, while the character stream handles translation between characters and bytes. FileReader, for example, uses FileInputStream, while FileWriter uses FileOutputStream.

There are two general-purpose byte-to-character "bridge" streams: InputStreamReader and OutputStreamWriter. Use them to create character streams when there are no prepackaged character stream classes that meet your needs.

Use: an OutputStreamWriter wrapped in a BufferedWriter. Same for a input stream. Avoid FileReader and FileWriter because you cannot specify the chartset.

Buffered streams

There are four buffered stream classes used to wrap unbuffered streams: BufferedInputStream and BufferedOutputStream create buffered byte streams, while BufferedReader and BufferedWriter create buffered character streams.A buffered stream might require to be flushed.

Data streams

  • DataInput
    • ObjectInput (also extends java.lang.AutoCloseable)
  • DataOutput
    • ObjectOutput (also extends java.lang.AutoCloseable)

Data streams support binary I/O of primitive data type values (boolean, char, byte, short, int, long, float, and double) as well as String values.

All data streams implement either the DataInput interface or the DataOutput interface. The most widely-used implementations of these interfaces are DataInputStream and DataOutputStream.

Object streams

Just as data streams support I/O of primitive data types, object streams support I/O of objects. The object stream classes are ObjectInputStream and ObjectOutputStream. These classes implement ObjectInput and ObjectOutput, which are subinterfaces of DataInput and DataOutput.