Java Programming
Mehdi Ebady Manaa
3rd class – Department of Network
College of IT- University of Babylon
1. Command-Line Arguments
Any Java technology application can use command-line arguments.
• These string arguments are placed on the command line to
launch the Java interpreter after the class name:
public class TestArgs {
public static void main (String [] args){
for (int i=0; i< args.length; i++)
System.out.println("args ["+i+"]is :" +args[i]);
}
}
• Each command-line argument is placed in the args array that
is passed to the static main method as below :
public class CallTest {
public static void main(String[] args) {
String args1[]={"seeyou","ali","mohammed"};
TestArgs xx= new TestArgs();
xx.main(args1);
}
}
2. I/O Stream Fundamentals
A stream is a flow of data from a source or to a sink
A source stream initiates the flow of data, also called an input
stream.
A sink stream terminates the flow of data, also called an output
stream.
Sources and sinks are also called Input streams and output streams
Types of node streams are files, memory, and pipes between
threads or processes.
Table 1: Fundamental Stream Classes
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Date: Sunday, December 01, 2013
Java Programming
Mehdi Ebady Manaa
3rd class – Department of Network
College of IT- University of Babylon
3. Data Within Streams
Java technology supports two types of streams: character and byte.
Input and output of character data is handled (implemented) by
subclass readers and writers.
Input and output of byte data is handled (implemented) by subclass
inputStream and OutputStream
3.1. Byte Streams
The following sections describe the fundamental byte stream
3.1.1 The InputStream Methods
The following three methods provide access to the data from the
input stream:
The three basic read methods are:
int read()
// return an int from input stream, which contains either a byte read
from the stream or a -1
int read(byte[] buffer)
// read the stream into a byte array and return the number of bytes
read
int read(byte[] buffer, int offset, int length)
// read the stream into a byte array and return the number of bytes
read , the two int arguments in the third method
indicate a sub range in the target array that needs to be
filled
Other methods include:
void close()
//it closes the stream
long skip(long n)
//this method discards the specified number of bytes from the stream.
3.1.2 The OutputStream Methods
These methods write to the output of stream:
The three basic write methods are:
void write(int c)//
void write(byte[] buffer)
void write(byte[] buffer, int offset, int length)
• Other methods include:
void close()
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Date: Sunday, December 01, 2013
Java Programming
Mehdi Ebady Manaa
3rd class – Department of Network
College of IT- University of Babylon
void flush()// output stream uses it to force write when the write
accumulate before committing
Example1: create inputstream and write it to file test.txt
import java.io.FileInputStream;
import java.io.InputStream;
public class InputStreamDemo {
public static void main(String[] args) throws Exception {
InputStream x = null;
int i;
char c;
try{
// new input stream created
x = new FileInputStream("C:\\test.txt");
System.out.println("Characters printed:");
// reads till the end of the stream
while((i=x.read())!=-1)
{
// converts integer to character
c=(char)i;
// prints character
System.out.print(c);
}
}catch(Exception e){
// if any I/O error occurs
e.printStackTrace();
}finally{
// releases system resources associated with this stream
if(x!=null)
x.close();
}
}
}
Example 2: create buffer of byte to read from input file stream
import
import
import
import
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java.io.BufferedReader;
java.io.FileInputStream;
java.io.InputStream;
java.io.InputStreamReader;
Date: Sunday, December 01, 2013
Java Programming
Mehdi Ebady Manaa
3rd class – Department of Network
College of IT- University of Babylon
public class BufferedReaderDemo {
public static void main(String[] args) throws Exception {
InputStream is = null;
InputStreamReader isr = null;
BufferedReader br = null;
try{
// open input stream test.txt for reading purpose.
is = new FileInputStream("c:/test.txt");
// create new input stream reader
isr = new InputStreamReader(is);
// create new buffered reader
br = new BufferedReader(isr);
// creates buffer
char[] cbuf = new char[is.available()];// is.available to
check the next invoking of byte
// reads characters to buffer.
br.read(cbuf);
// for each character in the buffer
for (char c:cbuf)
{
// if char is empty
if(c == (char)0)
{
c='&';
}
// prints characters
System.out.print(c);
}
}catch(Exception e){
e.printStackTrace();
}finally{
// releases resources associated with the streams
if(is!=null)
is.close();
if(isr!=null)
isr.close();
if(br!=null)
br.close();
}
}
}
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Date: Sunday, December 01, 2013
Java Programming
Mehdi Ebady Manaa
3rd class – Department of Network
College of IT- University of Babylon
Example 3: read and write in input and output stream
import java.io.*;
public class OutputStreamDemo {
public static void main(String[] args) {
byte[] b = {'h', 'e', 'l', 'l', 'o'};
try {
// create a new output stream
OutputStream os = new FileOutputStream("c:/test.txt");
// craete a new input stream
InputStream is = new FileInputStream("c:/test.txt");
// write something
os.write(b);
// read what we wrote
for (int i = 0; i < b.length; i++) {
System.out.print("" + (char) is.read());
}
} catch (Exception ex) {
ex.printStackTrace();
}
}
}
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Date: Sunday, December 01, 2013