Programming in Java CSCI 2220

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Programming in JavaCSCI 2220

• More I/O, Serialization

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Data Streams

• We saw last time how to treat streams as either
  streams of bytes or streams of characters
• Sometimes we want an even higher level of
  abstraction and wish to read and write data to
  and from streams in the form of primitive data
  variables or entire class objects
• Save program state information to a file
• Send data variables to different threads,
  processes, or across network streams
• Many other examples
• Java has built in stream classes that
  automatically handle converting this information
  into the necessary raw bytes that a stream can use

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DataInputStreamDataOutputStream

• The DataInputStream and DataOutputStream classes
  respectively allow you to read and write
  primitive data types to input and output streams

BufferedOutputStream bufStream DataOutputStream
dataStream try bufStream new
BufferedOutputStream(new FileOutputStream(file.ou
t) dataStream new DataOutputStream(bufStrea
m) dataStream.writeInt(5)
catch(IOException e) System.err.println(Erro
r writing to file) finally try
dataStream.close() bufStream.close()
catch(IOException e) System.err.println(E
rror closing file)
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DataInputStreamDataOutputStream

• DataInputStream
• readBoolean()
• readByte()
• readChar()
• readDouble()
• readFloat()
• readInt()
• readLong()
• readShort()
• DataOutputStream has corresponding write methods

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ObjectInputStreamObjectOutputStream

• Since usually our programs do not consist of only
  primitive data types, we also may wish to read
  and write class objects to streams
• We can do this with the ObjectInputStream and
  ObjectOutputStream
• In fact, the ObjectInputStream and
  ObjectOutputStream classes provide the same
  functionality as DataInputStream and
  DataOutputStream, except they also include
  support for reading and writing object data via
  readObject() and writeObject() methods

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Serialization

• Objects can only be written to a stream if they
  are of a class type that implements the
  Serializable interface
• Most built in classes in Java implement
  Serializable
• Serializable does not define any methods. So in
  order to make a user defined class capable of
  being written to a stream, usually you can just
  append implements Serializable to the class
  declaration and it will work

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Serialization

• A somewhat obvious stipulation of writing objects
  to streams is that not only does the class need
  to implement Serializable, but all of the members
  of the class must also be Serializable
• If a member of the class is not Serializable, it
  can be declared transient and when the object is
  written to a stream, that member will be written
  with a value of null

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Homework 5

• Thats all for today
• Remember Homework 5 is due in one week