Object Input/Output

1
Object Input/Output
2
Object I/O

• To write objects to a file, we use
  ObjectOutputStream
• To read objects from a file we use
  ObjectInputStream
• Lets see how we write Person objects to a file
• First we need to modify the definition of the
  Person class in order to perform object I/O

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Object I/O

• If you want to perform an object I/O, then the
  class definition must include the phrase
  implements Serializable
• import java.io.
• class person implements Serializable
• // the rest is the same

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Object I/O

• If a class is a subclass, then the class
  definition must also change.

5
Object I/O

• You need File, FileInputStream, ObjectInputStream
  FileOutputStream, and ObjectOutputStream objects
  to do object I/O.
• To write a Person object to a file, we first
  create an ObjectOutputStream object

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Object I/O
File outFile new File ("objects.
txt") FileOutputStream outFileStream new
FileOutputStream (outFile) ObjectOutputStream
outObjectStream new ObjectOutputStream
(outFileStream) To save a Person object, we
write Person person new Person ("mR.
eXPRESSO", 20, 'm') OutObjectStream.writeObject
(person)
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It is possible to save different types of objects
to a single file. Assuming the Account and Bank
classes are defined properly, we can save both
types of objects to a single file Account
account 1, account 2 Bank bank1,
bank2 account1 new Account() account2 new
Account() bank 1 new Bank() bank2 new
Bank() outObjectStream.writeObject (account
1) outObjectStream.writeObject (account
2) outObjectStream.writeObject (bank
1) outObjectStream.writeObject (bank 2)
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You can even mix objects and primitives! outObject
Stream.writeObject (account 1) outObjectStream.wr
iteInt (15)
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Object I/O

• To read objects from a file, we use
  FileInputStream and ObjectInputStream
• We can use the method readObject to read an
  object.
• Since we can store any type of objects to a
  single file, we need to cast the object read from
  the file.
• Heres an example of reading a person object we
  saved in the file objects.data

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Reading Objects
File inFile new File("objects.txt") FileInputSt
ream inFileStream new FileInputStream
(inFile) ObjectInputStream inObjectStream new
ObjectInputStream (inFileStream) Person person
(Person) inObjectStream.readObject()
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See Handout Examples 1 and 2