? 2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 11 - 1
Chapter 11
File Input and Output
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 11 - 2
Chapter 11 Objectives
After you have read and studied this chapter,you should be able to
Include a FileDialog object in your program to let the
user specify a file.
Write bytes to a file and read them back from the file
using FileOutputStream and FileInputStream.
Write values of primitive data types to a file and read
them back from the file using DataOutputStream and
DataInputStream,
Write text data to a file and read them back from the file
using PrintWriter and BufferedReader,
Write objects to a file and read them back from the file
using ObjectOutputStream and ObjectInputStream.
Write exception-handling routines using the try–catch
block.
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 11 - 3
File Objects
To operate on a file,we must first create a File object (from java.io),
File inFile = new File(“sample.dat”);
File inFile
= new File(“C:\\SamplePrograms”,
“one.txt”);
File inFile = new File
(“C:/SamplePrograms/test.dat”);
Opens the file sample.dat
in the current directory.
Opens the file one.txt in
the directory
C:\SamplePrograms,
Notice the use of the
escape character \.
Opens the file test.dat in
the directory
C:\SamplePrograms
using the generic file
separator / and providing
the full pathname,
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 11 - 4
Some File Methods
if ( inFile.exists( ) ) { … }
if ( inFile.isFile( ) ) { … }
File folder = new
File(“C:/JavaProjects/Ch11”);
String filename[ ] = folder.list( );
for (int i=0; i < filename.length; i++ ){
outputBox.printLine( filename[i] );
}
To see if inFile is
associated to a real file
correctly.
To see if inFile is
associated to a file or a
directory.
List the name of all files
in the directory
C:\JavaProjects\Ch11,
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 11 - 5
FileDialog - Open
FileDialog is a standard file dialog for selecting a file,
FileDialog fileBox = new FileDialog( mainWindow,“Open”,
FileDialog.LOAD );
fileBox.setVisible( true );
String filename = fileBox.getFile( );
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 11 - 6
FileDialog - Save
FileDialog fileBox = new FileDialog( mainWindow,“Save As”,
FileDialog.SAVE );
fileBox.setVisible( true );
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 11 - 7
Low-Level File I/O – Output
//set up file and stream
File outFile = new File("sample1.data");
FileOutputStream
outStream = new FileOutputStream( outFile );
//data to save
byte[] byteArray = {10,20,30,40,
50,60,70,80};
//write data to the stream
outStream.write( byteArray );
//output done,so close the stream
outStream.close();
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 11 - 8
Low-Level File I/O – Input
//set up file and stream
File inFile = new File("sample1.data");
FileInputStream inStream = new FileInputStream(inFile);
//set up an array to read data in
int fileSize = (int)inFile.length();
byte[] byteArray = new byte[fileSize];
//read data in and display them
inStream.read(byteArray);
for (int i = 0; i < fileSize; i++) {
outputBox.printLine(byteArray[i]);
}
//input done,so close the stream
inStream.close();
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 11 - 9
High-Level File I/O – Output
File outFile = new File("sample2.data");
FileOutputStream outFileStream = new FileOutputStream(outFile);
DataOutputStream outDataStream = new DataOutputStream(outFileStream);
Primitive data type
values are written to
outDataStream.
Primitive data type
values are
converted to bytes.
Converted bytes
are written to the
file.
outDataStream
writeFloat
writeInt
writeDouble
1
outFileStream
2
outFile
3
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 11 - 10
High-Level File I/O – Input
File inFile = new File("sample2.data");
FileInputStream inFileStream = new FileInputStream(inFile);
DataInputStream inDataStream = new DataInputStream(inFileStream);
Primitive data type
values are read from
inDataStream.
Bytes are converted
to primitive data
type values.
Bytes are read from
the file.
readFloat
readInt
readDouble
3
inDataStream
2
inFileStream
outFile
1
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 11 - 11
Textfile I/O – Output
//set up file and stream
File outFile = new File("sample3.data");
FileOutputStream outFileStream = new FileOutputStream(outFile);
PrintWriter outStream = new PrintWriter(outFileStream);
//write values of primitive data types to the stream
outStream.println(987654321);
outStream.println(11111111L);
//…
outStream.println('A');
outStream.println(true);
//output done,so close the stream
outStream.close();
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 11 - 12
Textfile I/O – Input
//set up file and stream
File inFile = new File("sample3.data");
FileReader fileReader = new FileReader(inFile);
BufferedReader bufReader = new BufferedReader(fileReader);
String str;
//get integer
str = bufReader.readLine();
int i = Convert.toInt(str);
//read other data in a similar manner
//input done,so close the stream
bufReader.close();
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 11 - 13
Handling Exceptions
An exception occurs when any of the semantic
constraints of the Java language is violated.
An exception is said to be thrown and caught,
When our program calls a statement that can throw
an exception,we must write a code to either
propagate the thrown exception or
handle it by the try-block statement.
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 11 - 14
Propagation Approach
Add the phrase throws <Exception> to the
declaration for a method that includes a call to a
statement that can throw exceptions,Replace
<Exception> with the actual exception class,such as IOException,EOFException,and so forth.
void computeSum (String fileName ) throws IOException
{
File inFile = new File(fileName);
FileInputStream inFileStream = new FileInputStream(inFile);
DataInputStream inDataStream = new DataInputStream(inFileStream);
//read three integers
int i = inDataStream.readInt();
int j = inDataStream.readInt();
int k = inDataStream.readInt();
sum = i + j + k;
inDataStream.close();
}
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 11 - 15
try-catch Approach
Use the try-catch statement to include the exception-handling routines.
void computeSum (String fileName )
{
success = true;
try {
File inFile = new File(fileName);
FileInputStream inFileStream = new FileInputStream(inFile);
DataInputStream inDataStream = new DataInputStream(inFileStream);
//read three integers
int i = inDataStream.readInt();
int j = inDataStream.readInt();
int k = inDataStream.readInt();
sum = i + j + k;
inDataStream.close();
}
catch (IOException e) {
success = false;}
}
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 11 - 16
Handling Multiple Exceptions
You can have more than one catch clause for each try.
try {
...
}
catch (FileNotFoundException e) {
success = false;
System.out.println("File " + fileName + " does not exist.");
}
catch (EOFException e) {
success = false;
System.out.println("Error," +
"Cannot read beyond end of file");
}
catch (IOException e) {
success = false;
System.out.println("General I/O exception is thrown");
}
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 11 - 17
Object File I/O
It is possible to store objects just as easily as you
store primitive data values.
We use ObjectOutputStream and ObjectInputStream
to save to and load objects from a file.
To save objects from a given class,the class
declaration must include the phrase implements
Serializable,For example,
class Person implements Serializable
{
.,,
}
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 11 - 18
Saving Objects
File outFile
= new File("objects.data");
FileOutputStream outFileStream
= new FileOutputStream(outFile);
ObjectOutputStream outObjectStream
= new ObjectOutputStream(outFileStream);
Person person = new Person("Mr,Espresso",20,'M');
outObjectStream.writeObject( person );
account1 = new Account();
bank1 = new Bank();
outObjectStream.writeObject( account1 );
outObjectStream.writeObject( bank1 );
Could save objects
from the different
classes.
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 11 - 19
Loading Objects
File inFile
= new File("objects.data");
FileInputStream inFileStream
= new FileInputStream(inFile);
ObjectInputStream inObjectStream
= new ObjectInputStream(inFileStream);
Person person
= (Person) inObjectStream.readObject( );
Account account1
= (Account) inObjectStream.readObject( );
Bank bank1
= (Bank) inObjectStream.readObject( );
Must read in the
correct order.
Must type cast
to the correct
object type.
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 11 - 20
Saving and Loading Arrays
Instead of processing array elements individually,it is possible to save and load the whole array at once.
Person[] people = new Person[ N ]; //assume N already has a value
//build the people array
.,,
//save the array
outObjectStream.writeObject ( people );
//load the array
Person[ ] people = (Person[ ]) inObjectStream.readObject ( );
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 11 - 21
Sample Class,Saving an AddressBook
Problem Statement
Write a class that manages file I/O of an AddressBook object.
Capabilities
Allows the programmer to specify the file.
Saves the address book to a programmer-designated
file.
Loads the address book from a programmer-designated
file,
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 11 - 22
Development Steps
1,Implement the constructor and the setFile method.
2,Implement the write method.
3,Implement the read method.
4,Finalize the class.
The End
Chapter 11
File Input and Output
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 11 - 2
Chapter 11 Objectives
After you have read and studied this chapter,you should be able to
Include a FileDialog object in your program to let the
user specify a file.
Write bytes to a file and read them back from the file
using FileOutputStream and FileInputStream.
Write values of primitive data types to a file and read
them back from the file using DataOutputStream and
DataInputStream,
Write text data to a file and read them back from the file
using PrintWriter and BufferedReader,
Write objects to a file and read them back from the file
using ObjectOutputStream and ObjectInputStream.
Write exception-handling routines using the try–catch
block.
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 11 - 3
File Objects
To operate on a file,we must first create a File object (from java.io),
File inFile = new File(“sample.dat”);
File inFile
= new File(“C:\\SamplePrograms”,
“one.txt”);
File inFile = new File
(“C:/SamplePrograms/test.dat”);
Opens the file sample.dat
in the current directory.
Opens the file one.txt in
the directory
C:\SamplePrograms,
Notice the use of the
escape character \.
Opens the file test.dat in
the directory
C:\SamplePrograms
using the generic file
separator / and providing
the full pathname,
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 11 - 4
Some File Methods
if ( inFile.exists( ) ) { … }
if ( inFile.isFile( ) ) { … }
File folder = new
File(“C:/JavaProjects/Ch11”);
String filename[ ] = folder.list( );
for (int i=0; i < filename.length; i++ ){
outputBox.printLine( filename[i] );
}
To see if inFile is
associated to a real file
correctly.
To see if inFile is
associated to a file or a
directory.
List the name of all files
in the directory
C:\JavaProjects\Ch11,
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 11 - 5
FileDialog - Open
FileDialog is a standard file dialog for selecting a file,
FileDialog fileBox = new FileDialog( mainWindow,“Open”,
FileDialog.LOAD );
fileBox.setVisible( true );
String filename = fileBox.getFile( );
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 11 - 6
FileDialog - Save
FileDialog fileBox = new FileDialog( mainWindow,“Save As”,
FileDialog.SAVE );
fileBox.setVisible( true );
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 11 - 7
Low-Level File I/O – Output
//set up file and stream
File outFile = new File("sample1.data");
FileOutputStream
outStream = new FileOutputStream( outFile );
//data to save
byte[] byteArray = {10,20,30,40,
50,60,70,80};
//write data to the stream
outStream.write( byteArray );
//output done,so close the stream
outStream.close();
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 11 - 8
Low-Level File I/O – Input
//set up file and stream
File inFile = new File("sample1.data");
FileInputStream inStream = new FileInputStream(inFile);
//set up an array to read data in
int fileSize = (int)inFile.length();
byte[] byteArray = new byte[fileSize];
//read data in and display them
inStream.read(byteArray);
for (int i = 0; i < fileSize; i++) {
outputBox.printLine(byteArray[i]);
}
//input done,so close the stream
inStream.close();
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 11 - 9
High-Level File I/O – Output
File outFile = new File("sample2.data");
FileOutputStream outFileStream = new FileOutputStream(outFile);
DataOutputStream outDataStream = new DataOutputStream(outFileStream);
Primitive data type
values are written to
outDataStream.
Primitive data type
values are
converted to bytes.
Converted bytes
are written to the
file.
outDataStream
writeFloat
writeInt
writeDouble
1
outFileStream
2
outFile
3
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 11 - 10
High-Level File I/O – Input
File inFile = new File("sample2.data");
FileInputStream inFileStream = new FileInputStream(inFile);
DataInputStream inDataStream = new DataInputStream(inFileStream);
Primitive data type
values are read from
inDataStream.
Bytes are converted
to primitive data
type values.
Bytes are read from
the file.
readFloat
readInt
readDouble
3
inDataStream
2
inFileStream
outFile
1
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 11 - 11
Textfile I/O – Output
//set up file and stream
File outFile = new File("sample3.data");
FileOutputStream outFileStream = new FileOutputStream(outFile);
PrintWriter outStream = new PrintWriter(outFileStream);
//write values of primitive data types to the stream
outStream.println(987654321);
outStream.println(11111111L);
//…
outStream.println('A');
outStream.println(true);
//output done,so close the stream
outStream.close();
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 11 - 12
Textfile I/O – Input
//set up file and stream
File inFile = new File("sample3.data");
FileReader fileReader = new FileReader(inFile);
BufferedReader bufReader = new BufferedReader(fileReader);
String str;
//get integer
str = bufReader.readLine();
int i = Convert.toInt(str);
//read other data in a similar manner
//input done,so close the stream
bufReader.close();
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 11 - 13
Handling Exceptions
An exception occurs when any of the semantic
constraints of the Java language is violated.
An exception is said to be thrown and caught,
When our program calls a statement that can throw
an exception,we must write a code to either
propagate the thrown exception or
handle it by the try-block statement.
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 11 - 14
Propagation Approach
Add the phrase throws <Exception> to the
declaration for a method that includes a call to a
statement that can throw exceptions,Replace
<Exception> with the actual exception class,such as IOException,EOFException,and so forth.
void computeSum (String fileName ) throws IOException
{
File inFile = new File(fileName);
FileInputStream inFileStream = new FileInputStream(inFile);
DataInputStream inDataStream = new DataInputStream(inFileStream);
//read three integers
int i = inDataStream.readInt();
int j = inDataStream.readInt();
int k = inDataStream.readInt();
sum = i + j + k;
inDataStream.close();
}
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 11 - 15
try-catch Approach
Use the try-catch statement to include the exception-handling routines.
void computeSum (String fileName )
{
success = true;
try {
File inFile = new File(fileName);
FileInputStream inFileStream = new FileInputStream(inFile);
DataInputStream inDataStream = new DataInputStream(inFileStream);
//read three integers
int i = inDataStream.readInt();
int j = inDataStream.readInt();
int k = inDataStream.readInt();
sum = i + j + k;
inDataStream.close();
}
catch (IOException e) {
success = false;}
}
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 11 - 16
Handling Multiple Exceptions
You can have more than one catch clause for each try.
try {
...
}
catch (FileNotFoundException e) {
success = false;
System.out.println("File " + fileName + " does not exist.");
}
catch (EOFException e) {
success = false;
System.out.println("Error," +
"Cannot read beyond end of file");
}
catch (IOException e) {
success = false;
System.out.println("General I/O exception is thrown");
}
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 11 - 17
Object File I/O
It is possible to store objects just as easily as you
store primitive data values.
We use ObjectOutputStream and ObjectInputStream
to save to and load objects from a file.
To save objects from a given class,the class
declaration must include the phrase implements
Serializable,For example,
class Person implements Serializable
{
.,,
}
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 11 - 18
Saving Objects
File outFile
= new File("objects.data");
FileOutputStream outFileStream
= new FileOutputStream(outFile);
ObjectOutputStream outObjectStream
= new ObjectOutputStream(outFileStream);
Person person = new Person("Mr,Espresso",20,'M');
outObjectStream.writeObject( person );
account1 = new Account();
bank1 = new Bank();
outObjectStream.writeObject( account1 );
outObjectStream.writeObject( bank1 );
Could save objects
from the different
classes.
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 11 - 19
Loading Objects
File inFile
= new File("objects.data");
FileInputStream inFileStream
= new FileInputStream(inFile);
ObjectInputStream inObjectStream
= new ObjectInputStream(inFileStream);
Person person
= (Person) inObjectStream.readObject( );
Account account1
= (Account) inObjectStream.readObject( );
Bank bank1
= (Bank) inObjectStream.readObject( );
Must read in the
correct order.
Must type cast
to the correct
object type.
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 11 - 20
Saving and Loading Arrays
Instead of processing array elements individually,it is possible to save and load the whole array at once.
Person[] people = new Person[ N ]; //assume N already has a value
//build the people array
.,,
//save the array
outObjectStream.writeObject ( people );
//load the array
Person[ ] people = (Person[ ]) inObjectStream.readObject ( );
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 11 - 21
Sample Class,Saving an AddressBook
Problem Statement
Write a class that manages file I/O of an AddressBook object.
Capabilities
Allows the programmer to specify the file.
Saves the address book to a programmer-designated
file.
Loads the address book from a programmer-designated
file,
2000 McGraw-Hill Introduction to Object-Oriented Programming with Java--Wu Chapter 11 - 22
Development Steps
1,Implement the constructor and the setFile method.
2,Implement the write method.
3,Implement the read method.
4,Finalize the class.
The End
