INF120 Basics in JAVA Programming AUBG, COS dept, Fall semester 2013 Reference books: Malik D.S., Java Programming, From Problem Analysis to Program Design,

INF120Basics in JAVA Programming

AUBG, COS dept, Fall semester 2013

Reference books:

Malik D.S., Java Programming, From Problem Analysis to Program Design, Cengage Learning, 4e 2010

Farrell J. Java Programming, Cengage Learning, 5e 2010

Y.Daniel Liang, Introduction to JAVA Programming, Brief version, Pearson IE, Prentice Hall, 9e 2013

Any Java book available in AUBG library

Course lecturer: Assoc. Prof. Stoyan Bonev, PhD

INF120 Basics in JAVA ProgrammingAUBG, COS dept, Fall semester 2013

Lecture 34Title:

Files Input/Output(Text & Binary)

Reference: MalikFarrell, chap 1, Liang Ch19

Lecture Contents:

• The File class

• Text file I/O

• Binary file I/O

Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved.

Data stored in a program get lost when program exits.

To permanently store data created in a program, we need to save them in a file on a disk. Every file is saved in a directory in the file systemAn absolute file name (full name)

– C:\book\Welcome.javaA relative file name (relation to current directory)

– Welcome.javaA directory path

– C:\book

4

Liang, Introduction to Java Programming, Ninth Edition, (c) 2013 Pearson Education, Inc. All rights reserved. 5

The File ClassThe File class is intended to provide an abstraction that deals with most of the machine-dependent complexities of files and path names in a machine-independent fashion.

The filename is a string.

The File class is a wrapper class for the file name and its directory path.


The File ClassThe File class contains the methods:

for Obtaining the properties of a file/directory

for creating a directory only (not file)

for renaming a file/directory

for deleting a file/directory

However, the File class does not contain the methods for reading/writing the file contents.


Obtaining file properties and manipulating file.

java.io.File

+File(pathname: String)

+File(parent: String, child: String)

+File(parent: File, child: String)

+exists(): boolean

+canRead(): boolean

+canWrite(): boolean

+isDirectory(): boolean

+isFile(): boolean

+isAbsolute(): boolean

+isHidden(): boolean

+getAbsolutePath(): String

+getCanonicalPath(): String

+getName(): String

+getPath(): String

+getParent(): String

+lastModified(): long

+length(): long

+listFiles(): File[]

+delete(): boolean

+renameTo(dest: File): boolean

+mkdir(): boolean

+mkdirs(): boolean

Creates a File object for the specified pathname. The pathname may be a directory or a file.

Creates a File object for the child under the directory parent. The child may be a filename or a subdirectory.

Creates a File object for the child under the directory parent. The parent is a File object. In the preceding constructor, the parent is a string.

Returns true if the file or the directory represented by the File object exists.

Returns true if the file represented by the File object exists and can be read.

Returns true if the file represented by the File object exists and can be written.

Returns true if the File object represents a directory.

Returns true if the File object represents a file.

Returns true if the File object is created using an absolute path name.

Returns true if the file represented in the File object is hidden. The exact definition of hidden is system-dependent. On Windows, you can mark a file hidden in the File Properties dialog box. On UNIX systems, a file is hidden if its name begins with a period (.) character.

Returns the complete absolute file or directory name represented by the File object.

Returns the same as getAbsolutePath() except that it removes redundant names, such as "." and "..", from the pathname, resolves symbolic links (on UNIX), and converts drive letters to standard uppercase (on Windows).

Returns the last name of the complete directory and file name represented by the File object. For example, new File("c:\\book\\test.dat").getName() returns test.dat.

Returns the complete directory and file name represented by the File object. For example, new File("c:\\book\\test.dat").getPath() returns c:\book\test.dat.

Returns the complete parent directory of the current directory or the file represented by the File object. For example, new File("c:\\book\\test.dat").getParent() returns c:\book.

Returns the time that the file was last modified.

Returns the size of the file, or 0 if it does not exist or if it is a directory.

Returns the files under the directory for a directory File object.

Deletes the file or directory represented by this File object. The method returns true if the deletion succeeds.

Renames the file or directory represented by this File object to the specified name represented in dest. The method returns true if the operation succeeds.

Creates a directory represented in this File object. Returns true if the directory is created successfully.

Same as mkdir() except that it creates directory along with it parent directories if the parent directories do not exist.


Problem: Explore File Properties

TestFileClassTestFileClass

Objective: Write a program that demonstrates how to create files in a platform-independent way and use the methods in the File class to obtain their properties. The following figures show a sample run of the program on Windows and on Unix.


Problem: Explore File Properties

Run the TestFileClass.java program as it Is in the repository.

Modify the program to explore the properties of some file of your own.

Modify the program to explore the properties of the program file itself, i.e. TestFileClass.java


Text File I/O

Liang, Chapter 14


Text I/O

A File object encapsulates the properties of a file or a path, but does not contain the methods for reading/writing data from/to a file.

In order to perform I/O, you need to create objects using appropriate Java I/O classes. The objects contain the methods for reading/writing data from/to a file.


Text I/O

This section introduces how to read/write strings and numeric values from/to a text file using the

Scanner and

PrintWriter classes.


Writing Data Using PrintWriter

PrintWriter class is used to create a file and write data to a text file.

First, you create a PrintWriter object for a text file:

Then you can invoke methods print, println, printf on the PrintWriter object to write data to a file.

The close method is used to close the file


Writing Data Using PrintWriter

WriteDataWriteData

java.io.PrintWriter

+PrintWriter(filename: String)

+print(s: String): void

+print(c: char): void

+print(cArray: char[]): void

+print(i: int): void

+print(l: long): void

+print(f: float): void

+print(d: double): void

+print(b: boolean): void

Also contains the overloaded println methods.

Also contains the overloaded printf methods.

.

Creates a PrintWriter for the specified file.

Writes a string.

Writes a character.

Writes an array of character.

Writes an int value.

Writes a long value.

Writes a float value.

Writes a double value.

Writes a boolean value.

A println method acts like a print method; additionally it prints a line separator. The line separator string is defined by the system. It is \r\n on Windows and \n on Unix.

The printf method was introduced in §3.6, “Formatting Console Output and Strings.”


WriteData.java

Source textpublic class WriteData {

public static void main(String[] args) throws Exception{

java.io.File file = new java.io.File("scores.txt");

if (file.exists()) {

System.out.println("File already exists");

System.exit(0);

}

// Create a file

java.io.PrintWriter output =new java.io.PrintWriter(file);

// Write formatted output to the file

output.print("John T Smith "); output.println(90); output.print("Eric K Jones "); output.println(85);

// Close the file

output.close();

} }


Reading Data Using Scanner

Scanner breaks its input into tokens delimited by ws characters

To read from the keyboard, you create a scanner for System.in:

Scanner cin = new Scanner(System.in); To read from a file, you create a scanner for a

file:

Scanner filein = new Scanner(new File(filename));

17


Reading Data Using Scanner

java.util.Scanner

+Scanner(source: File)

+Scanner(source: String)

+close()

+hasNext(): boolean

+next(): String

+nextByte(): byte

+nextShort(): short

+nextInt(): int

+nextLong(): long

+nextFloat(): float

+nextDouble(): double

+useDelimiter(pattern: String): Scanner

Creates a Scanner that produces values scanned from the specified file.

Creates a Scanner that produces values scanned from the specified string.

Closes this scanner.

Returns true if this scanner has another token in its input.

Returns next token as a string.

Returns next token as a byte.

Returns next token as a short.

Returns next token as an int.

Returns next token as a long.

Returns next token as a float.

Returns next token as a double.

Sets this scanner’s delimiting pattern.

ReadDataReadData

ReadData.java.

Source textimport java.util.Scanner;

public class ReadData {

public static void main(String[] args) throws Exception {

// Create a File instance

java.io.File file = new java.io.File("scores.txt");

// Create a Scanner for the file

Scanner input = new Scanner(file);// Read data from a file while (input.hasNext()) {

String firstName = input.next(); String mi = input.next(); String lastName = input.next();

int score = input.nextInt();

System.out.println

( firstName + " " + mi + " " + lastName + " " + score);

}

input.close(); // Close the file

} }


How does Scanner work?Token reading methods: nextByte, nextShort, nextInt, nextLong, nextFloat, nextDouble. They read tokens separated by delimiters, by default delimiters are ws

How does an input method work?

A token reading method first skips any delimiters, then reads a token ending at a delimiter. The token is then automatically converted to a value of byte, short, int, long, float and double type

For next method, no conversion is performed.

Both next and nextLine methods read a string.

If a token does not match the expected type, an exception InputMismatchException will be thrown.


Practical task

Compile and run demo program SBJavaIOFromTextFile.java

Examine the source text: Writes data into a file TestData.txt and reads data from the file in the same program

Modify the program to add one more record with data for your three names and your score and store it in the file.

Modify the program to populate the file with three records (three names and score) followed by 5 records for capital cities like “Sofia – capital city of Bulgaria”


Problem: Replacing Text

Write a class named ReplaceText that replaces a string in a text file with a new string. The filename and strings are passed as command-line arguments as follows:

java ReplaceText sourceFile targetFile oldString newString

For example, invokingjava ReplaceText FormatString.java t.txt StringBuilder StringBuffer

replaces all the occurrences of StringBuilder by StringBuffer in FormatString.java and saves the new file in t.txt.

ReplaceTextReplaceText


(GUI) File Dialogs

ReadFileUsingJFileChooserReadFileUsingJFileChooser


Binary I/O

Liang, Chapter 19


Motivations

Data stored in a text file is represented in human-readable form.Data stored in a binary file is represented in binary form.You cannot read binary files. They are designed to be read by programs. For example, Java source programs are stored in text files and can be read by a text editor, but Java classes are stored in binary files and are read by the JVM. The advantage of binary files is that they are more efficient to process than text files.


How is text I/O Handled in Java?A File object encapsulates the properties of a file or a path, but does not contain the methods for reading/writing data from/to a file. In order to perform I/O, you need to create objects using appropriate Java I/O classes.

PrintWriter output = new PrintWriter("temp.txt");

output.println("Java 101");

output.close();

Scanner input = new Scanner(new File("temp.txt"));

System.out.println(input.nextLine());

Program

Input object created from an

input class

Output object created from an

output class

Input stream

Output stream

File

File 01011…1001

11001…1011


Text File vs. Binary File Data stored in a text file are represented in human-readable

form. Data stored in a binary file are represented in binary form. You cannot read binary files. Binary files are designed to be read by programs. For example, the Java source programs are stored in text files and can be read by a text editor, but the Java classes are stored in binary files and are read by the JVM. The advantage of binary files is that they are more efficient to process than text files.

Although it is not technically precise and correct, you can imagine that a text file consists of a sequence of characters and a binary file consists of a sequence of bits. For example, the decimal integer 199 is stored as the sequence of three characters: '1', '9', '9' in a text file and the same integer is stored as a byte-type value C7 in a binary file, because decimal 199 equals to hex C7.


Binary I/OText I/O requires encoding and decoding. The JVM converts a Unicode to a file specific encoding when writing a character and converts a file specific encoding to a Unicode when reading a character. Binary I/O does not require conversions. When you write a byte to a file, the original byte is copied into the file. When you read a byte from a file, the exact byte in the file is returned.

Text I/O program

The Unicode of the character

Encoding/ Decoding

Binary I/O program

A byte is read/written (b)

(a)

e.g.,

"199"

The encoding of the character is stored in the file

0x31

e.g.,

199 00110111

00110001 00111001 00111001

0x39 0x39

0xC7

The same byte in the file


Binary I/O Classes

InputStream

OutputStream

Object

ObjectOutputStream

FilterOutputStream

FileOutputStream

BufferedInputStream

DataInputStream

BufferedOutputStream

DataOutputStream

PrintStream

ObjectInputStream

FilterInputStream

FileInputStream

The abstract InputStream is the root class for reading binary data.

The abstract OuptputStream is the root class for writing binary data.


java.io.InputStream

+read(): int

+read(b: byte[]): int

+read(b: byte[], off: int, len: int): int

+available(): int

+close(): void

+skip(n: long): long

+markSupported(): boolean

+mark(readlimit: int): void

+reset(): void

Reads the next byte of data from the input stream. The value byte is returned as an int value in the range 0 to 255. If no byte is available because the end of the stream has been reached, the value –1 is returned.

Reads up to b.length bytes into array b from the input stream and returns the actual number of bytes read. Returns -1 at the end of the stream.

Reads bytes from the input stream and stores into b[off], b[off+1], …, b[off+len-1]. The actual number of bytes read is returned. Returns -1 at the end of the stream.

Returns the number of bytes that can be read from the input stream.

Closes this input stream and releases any system resources associated with the stream.

Skips over and discards n bytes of data from this input stream. The actual number of bytes skipped is returned.

Tests if this input stream supports the mark and reset methods.

Marks the current position in this input stream.

Repositions this stream to the position at the time the mark method was last called on this input stream.

The value returned is a byte as an int type.

InputStream


The value is a byte as an int type.

OutputStream

java.io.OutputStream

+write(int b): void

+write(b: byte[]): void

+write(b: byte[], off: int, len: int): void

+close(): void

+flush(): void

Writes the specified byte to this output stream. The parameter b is an int value. (byte)b is written to the output stream.

Writes all the bytes in array b to the output stream.

Writes b[off], b[off+1], …, b[off+len-1] into the output stream.

Closes this input stream and releases any system resources associated with the stream.

Flushes this output stream and forces any buffered output bytes to be written out.


FileInputStream/FileOutputStream

FileInputStream/FileOutputStream are for reading/writing bytes from/to files.All the methods in FileInputStream/FileOuptputStream are inherited from its superclasses.

InputStream

OutputStream

Object

ObjectOutputStream

FilterOutputStream

FileOutputStream

BufferedInputStream

DataInputStream


DataOutputStream

PrintStream

ObjectInputStream

FilterInputStream

FileInputStream


FileInputStreamTo construct a FileInputStream, use the following constructors:

public FileInputStream(String filename)

public FileInputStream(File file)

A java.io.FileNotFoundException would occur if you attempt to create a FileInputStream with a nonexistent file.


FileOutputStreamTo construct a FileOutputStream, use the following constructors:

public FileOutputStream(String filename)public FileOutputStream(File file)public FileOutputStream(String filename, boolean append)public FileOutputStream(File file, boolean append)

If the file does not exist, a new file would be created. If the file already exists, the first two constructors would delete the current contents in the file. To retain the current content and append new data into the file, use the last two constructors by passing true to the append parameter.

TestFileStreamTestFileStream


FileInputStream/FileOutputStream

Examine the TestFileStream.java source file

Run the compile TestFileStream.class class file


FilterInputStream/FilterOutputStream

Filter streams are streams that filter bytes for some purpose. The basic byte input stream provides a read method that can only be used for reading bytes. If you want to read integers, doubles, or strings, you need a filter class to wrap the byte input stream. Using a filter class enables you to read integers, doubles, and strings instead of bytes and characters. FilterInputStream and FilterOutputStream are the base classes for filtering data. When you need to process primitive numeric types, use DataInputStream and DataOutputStream to filter bytes.

InputStream

OutputStream

Object

ObjectOutputStream

FilterOutputStream

FileOutputStream

BufferedInputStream

DataInputStream


DataOutputStream

PrintStream

ObjectInputStream

FilterInputStream

FileInputStream


DataInputStream/DataOutputStreamDataInputStream reads bytes from the stream and converts them into appropriate primitive type values or strings.

InputStream

OutputStream

Object

ObjectOutputStream

FilterOutputStream

FileOutputStream

BufferedInputStream

DataInputStream


DataOutputStream

PrintStream

ObjectInputStream

FilterInputStream

FileInputStream

DataOutputStream converts primitive type values or strings into bytes and output the bytes to the stream.


DataInputStream

DataInputStream extends FilterInputStream and implements the DataInput interface.

java.io.DataInput

+readBoolean(): boolean

+readByte(): byte

+readChar(): char

+readFloat(): float

+readDouble(): float

+readInt(): int

+readLong(): long

+readShort(): short

+readLine(): String

+readUTF(): String

Reads a Boolean from the input stream.

Reads a byte from the input stream.

Reads a character from the input stream.

Reads a float from the input stream.

Reads a double from the input stream.

Reads an int from the input stream.

Reads a long from the input stream.

Reads a short from the input stream.

Reads a line of characters from input.

Reads a string in UTF format.

InputStream

FilterInputStream

DataInputStream

+DataInputStream( in: InputStream)


DataOutputStreamDataOutputStream extends FilterOutputStream and implements the DataOutput interface.

java.io.DataOutput

+writeBoolean(b: Boolean): void

+writeByte(v: int): void

+writeBytes(s: String): void

+writeChar(c: char): void

+writeChars(s: String): void

+writeFloat(v: float): void

+writeDouble(v: float): void

+writeInt(v: int): void

+writeLong(v: long): void

+writeShort(v: short): void

+writeUTF(s: String): void

Writes a Boolean to the output stream.

Writes to the output stream the eight low-order bits of the argument v.

Writes the lower byte of the characters in a string to the output stream.

Writes a character (composed of two bytes) to the output stream.

Writes every character in the string s, to the output stream, in order, two bytes per character.

Writes a float value to the output stream.

Writes a double value to the output stream.

Writes an int value to the output stream.

Writes a long value to the output stream.

Writes a short value to the output stream.

Writes two bytes of length information to the output stream, followed by the UTF representation of every character in the string s.

OutputStream

FilterOutputStream

DataOutputStream

+DataOutputStream( out: OutputStream)


Characters and Strings in Binary I/O A Unicode consists of two bytes. The writeChar(char c) method writes the Unicode of character c to the output. The writeChars(String s) method writes the Unicode for each character in the string s to the output.

Why UTF-8? What is UTF-8?

UTF-8 is a coding scheme that allows systems to operate with both ASCII and Unicode efficiently. Most operating systems use ASCII. Java uses Unicode. The ASCII character set is a subset of the Unicode character set. Since most applications need only the ASCII character set, it is a waste to represent an 8-bit ASCII character as a 16-bit Unicode character. The UTF-8 is an alternative scheme that stores a character using 1, 2, or 3 bytes. ASCII values (less than 0x7F) are coded in one byte. Unicode values less than 0x7FF are coded in two bytes. Other Unicode values are coded in three bytes.


Using DataInputStream/DataOutputStream

Data streams are used as wrappers on existing input and output streams to filter data in the original stream. They are created using the following constructors:

public DataInputStream(InputStream instream)public DataOutputStream(OutputStream outstream)

The statements given below create data streams. The first statement creates an input stream for file in.dat; the second statement creates an output stream for file out.dat.

DataInputStream infile = new DataInputStream(new FileInputStream("in.dat"));DataOutputStream outfile = new DataOutputStream(new FileOutputStream("out.dat"));

TestDataStreamTestDataStream


Using DataInputStream/DataOutputStream

Examine the TestDataStream.java source file

Run the compiled TestDataStream.class class file

TestDataStreamTestDataStream


BufferedInputStream/BufferedOutputStream are used to reduce the number of disk reads and

writes Using buffers to speed up I/O

InputStream

OutputStream

Object

ObjectOutputStream

FilterOutputStream

FileOutputStream

BufferedInputStream

DataInputStream


DataOutputStream

PrintStream

ObjectInputStream

FilterInputStream

FileInputStream

BufferedInputStream/BufferedOutputStream does not contain new methods. All the methods BufferedInputStream/BufferedOutputStream are inherited from the InputStream/OutputStream classes.


Constructing BufferedInputStream/BufferedOutputStream

// Create a BufferedInputStream

public BufferedInputStream(InputStream in)

public BufferedInputStream(InputStream in, int bufferSize)

// Create a BufferedOutputStream

public BufferedOutputStream(OutputStream out)

public BufferedOutputStream(OutputStreamr out, int bufferSize)


Object I/O

DataInputStream/DataOutputStream enables you to perform I/O for primitive type values and strings. ObjectInputStream/ObjectOutputStream enables you to perform I/O for objects in addition for primitive type values and strings.

InputStream

OutputStream

Object

ObjectOutputStream

FilterOutputStream

FileOutputStream

BufferedInputStream

DataInputStream


DataOutputStream

PrintStream

ObjectInputStream

FilterInputStream

FileInputStream

Optional


ObjectInputStream

ObjectInputStream extends InputStream and implements ObjectInput and ObjectStreamConstants.

java.io.ObjectInput

+readObject(): Object

Reads an object.

java.io.InputStream

java.io.ObjectInputStream

+ObjectInputStream(in: InputStream)

java.io.DataInput

ObjectStreamConstants


ObjectOutputStream

ObjectOutputStream extends OutputStream and implements ObjectOutput and ObjectStreamConstants.

java.io.ObjectOutput

+writeObject(o: Object): void

Writes an object.

java.io.OutputStream

java.io.ObjectOutputStream

+ObjectOutputStream(out: OutputStream)

java.io.DataOutput

ObjectStreamConstants


Using Object StreamsYou may wrap an ObjectInputStream/ObjectOutputStream on any InputStream/OutputStream using the following constructors:

// Create an ObjectInputStream

public ObjectInputStream(InputStream in)

// Create an ObjectOutputStream

public ObjectOutputStream(OutputStream out)

TestObjectOutputStreamTestObjectOutputStream RunRun

TestObjectInputStreamTestObjectInputStream RunRun


The Serializable Interface

Not all objects can be written to an output stream. Objects that can be written to an object stream is said to be serializable. A serializable object is an instance of the java.io.Serializable interface. So the class of a serializable object must implement Serializable.

The Serializable interface is a marker interface. It has no methods, so you don't need to add additional code in your class that implements Serializable.

Implementing this interface enables the Java serialization mechanism to automate the process of storing the objects and arrays.


The transient Keyword

If an object is an instance of Serializable, but it contains non-serializable instance data fields, can the object be serialized? The answer is no. To enable the object to be serialized, you can use the transient keyword to mark these data fields to tell the JVM to ignore these fields when writing the object to an object stream.


The transient Keyword, cont.Consider the following class: public class Foo implements java.io.Serializable { private int v1; private static double v2; private transient A v3 = new A(); }class A { } // A is not serializable

When an object of the Foo class is serialized, only variable v1 is serialized. Variable v2 is not serialized because it is a static variable, and variable v3 is not serialized because it is marked transient. If v3 were not marked transient, a java.io.NotSerializableException would occur.


Random Access Files

All of the streams you have used so far are known as read-only or write-only streams. The external files of these streams are sequential files that cannot be updated without creating a new file. It is often necessary to modify files or to insert new records into files. Java provides the RandomAccessFile class to allow a file to be read from and write to at random locations.


RandomAccessFile

Creates a RandomAccessFile stream with the specified File object and mode.

Creates a RandomAccessFile stream with the specified file name string and mode.

Closes the stream and releases the resource associated with the stream.

Returns the offset, in bytes, from the beginning of the file to where the next read or write occurs.

Returns the length of this file.

Reads a byte of data from this file and returns –1 an the end of stream.

Reads up to b.length bytes of data from this file into an array of bytes.

Reads up to len bytes of data from this file into an array of bytes.

Sets the offset (in bytes specified in pos) from the beginning of the stream to where the next read or write occurs.

Sets a new length of this file.

Skips over n bytes of input discarding the skipped bytes.

Writes b.length bytes from the specified byte array to this file, starting at the current file pointer.

Writes len bytes from the specified byte array starting at offset off to this file.

DataInput

DataInput

java.io.RandomAccessFile

+RandomAccessFile(file: File, mode: String)

+RandomAccessFile(name: String, mode: String)

+close(): void

+getFilePointer(): long

+length(): long

+read(): int

+read(b: byte[]): int

+read(b: byte[], off: int, len: int) : int

+seek(long pos): void

+setLength(newLength: long): void

+skipBytes(int n): int

+write(b: byte[]): void

+write(byte b[], int off, int len) +write(b: byte[], off: int, len: int):

void


File PointerA random access file consists of a sequence of bytes. There is a special marker called file pointer that is positioned at one of these bytes. A read or write operation takes place at the location of the file pointer. When a file is opened, the file pointer sets at the beginning of the file. When you read or write data to the file, the file pointer moves forward to the next data. For example, if you read an int value using readInt(), the JVM reads four bytes from the file pointer and now the file pointer is four bytes ahead of the previous location.

byte

file

byte

…

byte

byte

byte

byte

byte

…

byte

byte

byte

byte

byte

file pointer

byte

file

byte

…

byte

byte

byte

byte

byte

…

byte

byte

byte

byte

byte

file pointer

(A) Before readInt()

(B) Before readInt()


RandomAccessFile MethodsMany methods in RandomAccessFile are the same as those in DataInputStream and DataOutputStream. For example, readInt(), readLong(), writeDouble(), readLine(), writeInt(), and writeLong() can be used in data input stream or data output stream as well as in RandomAccessFile streams.


RandomAccessFile Methods, cont.

void seek(long pos) throws IOException;

Sets the offset from the beginning of the RandomAccessFile stream to where the next reador write occurs.

long getFilePointer() IOException;

Returns the current offset, in bytes, from thebeginning of the file to where the next reador write occurs.


RandomAccessFile Methods, cont.

long length()IOException

Returns the length of the file.

final void writeChar(int v) throws IOException

Writes a character to the file as a two-byte Unicode, with the high byte written first.

final void writeChars(String s)throws IOException

Writes a string to the file as a sequence ofcharacters.


RandomAccessFile Constructor

RandomAccessFile raf =new RandomAccessFile("test.dat", "rw"); //allows read and write

RandomAccessFile raf =new RandomAccessFile("test.dat", "r"); //read only


A Short Example on RandomAccessFile

TestRandomAccessFileTestRandomAccessFile

Thank You For

Your Attention!

Any Questions?

Documents

INF120 Basics in JAVA Programming AUBG, COS dept, Fall semester 2013 Reference books: Malik D.S., Java Programming, From Problem Analysis to Program Design,