Java Input Output and File Handling

Input/Output Streams
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Input/Output Concepts
 Data Storage
o Transient memory : RAM
• It is accessed directly by processor.
o Persistent Memory: Disk and Tape
• It requires I/O operations.
 I/O sources and destinations
o console, disk, tape, network, etc.
 Streams
o It represents a sequential stream of bytes.
o It hides the details of I/O devices.

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IO Stream– java.io package
101010 101010Byte Array Byte Array
1010 1010ABCD
Binary Data
•.exe
•.jpg
•.class
Text Data
•.txt
•.java
•.bat
ABCDThis is Line This is Line
InputStream
ByteByte
OutputStream
BufferedOutputStream
BufferedInputStream
BufferedWriter
BufferedReader
Writer Reader
Char
Line
Char Line
Byte
Byte
• FileWriter
• PrintWriter
• FileReader
• InputStreamReader
• Scanner
• FileOutputStream
• ObjectOutputStream
• FileInputStream
• ObjectInputStream

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Types Of Data
 character data
o Represented as 1-byte ASCII .
o Represented as 2-bytes Unicode within Java programs. The
first 128 characters of Unicode are the ASCII characters.
o Read by Reader and its subclasses.
o Written by Writer and its subclasses.
o You can use java.util.Scanner to read characters in
JDK1.5 onward.
 binary data
o Read by InputStream and its subclasses.
o Written by OutputStream and its subclasses.

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Attrib.java : c:>java Attrib <fileName>
import java.io.File; java.util.Date;
public static void main(String[] args) {
File f = new File("c:/temp/a.txt”");
// File f = new File("c:/temp” , “a.txt");
if(f.exists()){
System.out.println(“Name” + f.getName());
System.out.println("Absolute path: " + f.getAbsolutePath());
System.out.println(" Is writable “ + f.canWrite());
System.out.println(" Is readable“ + f.canRead());
System.out.println(" Is File“ + f.isFile());
System.out.println(" Is Directory“ + f.isDirectory());
System.out.println("Last Modified at " + new Date(f.lastModified()));
System.out.println(“Length " + f.length() + " bytes long.");
}
}
}

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Representing a File
 Class java.io.File represents a file or folder (directory).
o Constructors:
• public File (String path)
• public File (String path, String name)
o Interesting methods:
• boolean exists()
• boolean isDirectory()
• boolean isFile()
• boolean canRead()
• boolean canWrite()
• long length()
• long lastModified()

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Representing a File (Cont.)
More interesting methods:
o boolean delete()
o boolean renameTo(File dest)
o boolean mkdir()
o String[] list()
o File[] listFiles()
o String getName()

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Display file and subdirectories
This program displays files and subdirectories of
a directory.
File directory = new File("C:/temp");
//File directory = new File(args[0]);
String[] list = directory.list();
for (int i = 0; i < list.length; i++) {
System.out.println((i + 1) + " : " +
list[i]);
}
}

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Display only files from a folder
//File directory = new File(args[0]);
String[] list = directory.list();
File f = new File(“c:/temp”,list[i]);
if(f.isFile()){
System.out.println((i + 1) + " : " + list[i]);
}
}
}

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Display only files from a folder
File[] list = directory.listFiles();
if (list[i].isFile()) {
System.out.println((i + 1) + " : " + list[i].getName());
}
}
}

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FileReader- Read char from a file
public static void main(String[] args) throws Exception{
FileReader reader = new FileReader(“c:/test.txt”);
int ch = reader.read();
char chr;
while(ch != -1){
chr = (char)ch;
System.out.print( chr);
ch = reader.read();
}
}

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Read a file line by line
public static void main(String[] args) throws Exception {
FileReader reader = new FileReader("c:/test.txt");
BufferedReader br= new BufferedReader(reader);
String line = br.readLine();
while (line != null) {
System.out.println(line);
line = br.readLine();
}
reader.close();
}

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Read file by Line
1010
Text Data
•.txt
•.java
•.bat
ABCD This is Line
BufferedReader
FileReader
Char LineByte
Byte
Char
Line

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Write to a File
FileWriter writer = new FileWriter("c:/newtest.txt");
PrintWriter pw= new PrintWriter(writer);
for (int i = 0; i < 5; i++) {
pw.println(i + " : Line");
}
pw.close();
writer.close();
System.out.println(“File is successfully written, Pl check c:/newtest.txt ");
}

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Write to a File
1010ABCD
•Text Data
•.txt
•.java
•.bat
This is Line
PrintWriter
FileWriter
Char
Line
Byte
Contains print and println methods
Line
Char
Byte

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Append Text/Bytes in existing File
 FileWriter: You may use either constructor to create a
FileWriter object to append text in an existing file.
o FileWriter(“c:a.txt”,true)
o FileWriter(new File(“c:a.txt”),true)
 FileOutputStream: You may use either constructor to create a
FileOutputStream object to append bytes in an existing binary
file.
o FileOutputStream (“c:a.jpg”,true)
o FileOutputStream (new File(“c:a.jpg”),true)

Copy A Text File
 String source= "c:/a.txt";
 String target = "c:/b.txt";
 FileReader reader = new FileReader(source);
 FileWriter writer = new FileWriter(target);
 int ch = reader.read() ;
 while (ch != -1){
o writer.write(ch);
o ch = reader.read();
 }
 writer.close();
 reader.close();
 System.out.println(source + " is copied to "+ target);
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Copy A Binary File
 String source= "c:/IMG_0046.JPG";
 String target = "c:/baby.jpg";
 FileInputStream reader = new FileInputStream(source);
 FileOutputStream writer = new FileOutputStream(target);
 int ch = reader.read() ;
 while (ch != -1){
o writer.write(ch);
o ch = reader.read();
 }
 writer.close();
 reader.close();
 System.out.println(source + " is copied to "+ target);
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Convert Binary to Text Stream
Class : InputStreamReader
Reads Data From Keyboard
o InputStreamReader ir= new InputStreamReader(System.in);
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1010
ABCD
CharByte
InputStreamReader

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Copycon command
 Reads data from keyboard and writes into a file
 String target= "c:/temp.txt";
 FileWriter writer = new FileWriter(target);
 PrintWriter printWriter = new PrintWriter(writer);
 InputStreamReader isReader = new InputStreamReader(System.in);
 BufferedReader in = new BufferedReader(isReader );
 String line = in.readLine();
 while (!line.equals("quit")) {
o printWriter.print(line);
o line = in.readLine();
 }
 printWriter.close();
 isReader.close();

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Serialization
 public class Employee implements Serializable {
 private int id;
 private String firstName;
 private String lastName;
 private Address add;
 private transient String tempValue;
 public Employee() { //Default Constructor }
 public Employee(int id, String firstName, String lastName) {
o this.id = id;
o this.firstName = firstName;
o this.lastName = lastName;
 }
 //accessor methods

Serialization
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Why Serialization ?
When an object is persisted in a file.
When an object is sent over the Network.
When an object is sent to Hardware.
Or in other words when an object is sent Out of
JVM.
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Persist/Write an Object
 FileOutputStream file = new
FileOutputStream("c:/object.ser");
 ObjectOutputStream out = new ObjectOutputStream(file);
 Employee emp = new Employee(10, “Sachin", “10lukar");
 out.writeObject(emp);
 out.close();
 System.out.println("Object is successfully persisted");
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Read an Object
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 FileInputStream file= new FileInputStream("c:/object.ser")
 ObjectInputStream in = new ObjectInputStream(file);
 Employee emp = (Employee) in.readObject();
 System.out.println("ID : " + emp.getId());
 System.out.println("F Name : " + emp.getFirstName());
 System.out.println("L Name : " + emp.getLastName());
 System.out.println("Temp Value: " + emp.getTempValue());
 NOTE : transient variables will be discarded during serialization

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Write Primitive Data
What are primitive data types?
o int
o double
o float
o boolean
o char
Which classes to use?
o DataInputStream
o DataOutputStream

Write Primitive Data
 public static void main(String[] args) throws Exception {
o FileOutputStream file = new
FileOutputStream("c:/primitivedata.dat");
o DataOutputStream out = new DataOutputStream(file);
o out.writeInt(1);
o out.writeBoolean(true);
o out.writeChar('A');
o out.writeDouble(1.2);
o out.close();
o file.close()
o System.out.println("Primitive Data successfully written");
 }
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Read Primitive Data
 public static void main(String[] args) throws Exception {
o FileInputStream file = new
FileInputStream("c:/primitivedata.dat");
o DataInputStream in = new DataInputStream(file);
o System.out.println(in.readInt());
o System.out.println(in.readBoolean());
o System.out.println(in.readChar());
o System.out.println(in.readDouble());
o in.close();
 }
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Primitive File - Write
long dataPosition = 0; // to be determined later
RandomAccessFile in = new RandomAccessFile("datafile.dat", "rw");
// Write to the file.
in.writeLong(0); // placeholder
in.writeChars("blahblahblah");
dataPosition = in.getFilePointer();
in.writeInt(123);
in.writeBytes(“Blahblahblah");
// Rewrite the first byte to reflect updated data position.
in.seek(0);
in.writeLong(dataPosition);
in.close();
}

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Primitive File - Read
long dataPosition = 0;
int data = 0;
RandomAccessFile raf = new RandomAccessFile("datafile", "r");
// Get the position of the data to read.
dataPosition = raf.readLong();
System.out.println("dataPosition : " + dataPosition);
// Go to that position.
raf.seek(dataPosition);
// Read the data.
data = raf.readInt();
raf.close();
System.out.println("The data is: " + data);
}

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java.util.Scanner
 A simple text scanner which can parse primitive data
types and strings using regular expressions.
 Reads character data as Strings, or converts to primitive
values.
 Does not throw checked exceptions.
 Constructors
o Scanner (File source) // reads from a file
o Scanner (InputStream source) // reads from a stream
o Scanner (String source) // scans a String

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java.util.Scanner
Interesting methods:
o boolean hasNext()
o boolean hasNextInt()
o boolean hasNextDouble()
o …
o String next()
o String nextLine()
o int nextInt()
o double nextDouble()

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Read File By Scanner
public static void main(String[] args) throws Exception{
FileReader reader = new FileReader("c:/newtest.txt");
Scanner sc = new Scanner(reader);
while(sc.hasNext()){
System.out.println(sc.nextLine());
}
reader.close();
}

Token A String
Breaks string into tokens.
 public static void main(String[] args) {
o String str = “This is Java, Java is Object Oriented
Language, Java is guarantee for job";
o StringTokenizer stn = new StringTokenizer(str, ",");
o String token = null;
o while (stn.hasMoreElements()) {
o token = stn.nextToken();
o System.out.println(“Token is : " + token);
o }
 }
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Summary
 What is IO Package
o java.io
 How to represent a File/Directory
o File f = new File(“c:/temp/myfile.txt”)
• OR
o File f = new File(“c:/temp”,”myfile.txt”)

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Summary (Cont.)
How to write text data char by char?
o FileWriter out = new FileWrite(f);
• OR
o FileWriter out = new FileWrite (“c:/temp/myfile.txt”);
o out.write(‘A’);
How to write text data line by line?
o PrintWriter pOut = new PrintWriter(out);
o pOut.println(“This is Line”);

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Summary (Cont.)
How to read text data char by char?
o FileReader in = new FileReader(f);
• OR
o FileReader in = new FileReader (“c:/temp/myfile.txt”);
o in.read();
How to read text data line by line?
o BufferedReader pIn= new BufferedReader(in);
o pIn.readLine();
o Scanner.readLine()

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Summary (Cont.)
How to write binary data byte by byte?
o FileOutputStream out = new FileOutputStream(f);
• OR
o FileOutputStream out = new FileOutputStream
(“c:/temp/myfile.txt”);
o out.write(1);
How to write binary data as byte array?
o BufferedOutputStream bOut = new BufferedOutputStream
(out);
o bOut.write(byte[]);

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Summary (Cont.)
 How to read binary data byte by byte?
o FileInputStream in = new FileInputStream(f);
• OR
o FileInputStream in = new FileInputStream
(“c:/temp/myfile.txt”);
o in.read();
 How to read binary data as byte array?
o BufferedInputStream bIn = new BufferedInputStream (in);
o byte[] buffer = new byte[256];
o bIn.read(buffer);

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Summary (Cont.)
How to write primitive data?
o FileOutputStream file = new
FileOutputStream("c:/primitivedata.dat");
o DataOutputStream out = new DataOutputStream(file);
How to Read primitive data?
o FileInputStream file = new
FileInputStream("c:/primitivedata.dat");
o DataInputStream in = new DataInputStream(file);

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Summary (Cont.)
 How to persist/write an Object
o Make object Serialized
o FileOutputStream file = new FileOutputStream("c:/object.ser");
o ObjectOutputStream out = new ObjectOutputStream(file);
o out.writeObject(obj);
 How to read an Object
o FileInputStream file = new FileInputStream("c:/object.ser");
o ObjectInputStream in = new ObjectInputStream(file);
o Object obj = in.readObject();

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Byte to Char Stream
How to convert byte stream into char stream
o Use InputStreamReader
o InputStreamReader inputStreamReader
= new InputStreamReader(System.in);

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IO Hierarchy - InputSteam
 java.io.File
 java.io.RandomAccessFile
 java.io.InputStream
o java.io.ByteArrayInputStream
o java.io.FileInputStream
o java.io.FilterInputStream
• java.io.BufferedInputStream
• java.io.DataInputStream
• java.io.
LineNumberInputStream
o java.io.ObjectInputStream
o java.io.
StringBufferInputStream
 java.io.OutputStream
o java.io.ByteArrayOutputStream
o java.io.FileOutputStream
o java.io.FilterOutputStream
• java.io.BufferedOutputStream
• java.io.DataOutputStream
• java.io.PrintStream
o java.io.ObjectOutputStream

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IO Hierarchy - Reader
 java.io.Reader
o java.io.BufferedReader
• java.io.LineNumberReader
o java.io.CharArrayReader
o java.io.InputStreamReader
• java.io.FileReader
o java.io.StringReader
 java.io.Writer
o java.io.BufferedWriter
o java.io.CharArrayWriter
o java.io.OutputStreamWriter
• java.io.FileWriter
o java.io.PrintWriter
o java.io.StringWriter

Thank You!
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Java Input Output and File Handling

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