Create a fan of processes and chain of processes. Ask the user for the number of processes to be created.

CODE: (i) CHAIN PROCESS

#include <stdio.h>

#include<unistd.h>

void main()

{

  pid_t cid=0;

int n,i,a=5,j;

printf("enter numbers of Processes");

scanf("%d",&n);

for(i=0;i<n;i++)

{

 cid=fork();

 if(cid!=0)

 {

   printf("%d Process id:%d Child:%d\n",i,getpid(),cid);

   break;

 }

}

}

OUTPUT:

(ii) FAN PROCESS

#include <stdio.h>

#include<unistd.h>

void main()

{

  pid_t cid=0;

int n,i,a=5,j;

printf("enter numbers of Processes");

scanf("%d",&n);

for(i=0;i<n;i++)

{

 cid=fork();

 if(cid!=0)

 {

   printf("%d Process id:%d Child:%d\n",i,getpid(),cid);

 }

 else

    break;

}

}

OUTPUT:

Program that will create a new child process using fork() system call.

The fork() System Call:

System call fork() is used to create processes. It takes no arguments and returns a process ID. The purpose of fork() is to create a new process, which becomes the child process of the caller. After a new child process is created, both processes will execute the next instruction following the fork() system call. Therefore, we have to distinguish the parent from the child. This can be done by testing the returned value of fork():

• If fork() returns a negative value, the creation of a child process was unsuccessful.
• fork() returns a zero to the newly created child process.
• fork() returns a positive value, the process ID of the child process, to the parent. The returned process ID is of type pid_t defined in sys/types.h. Normally, the process ID is an integer. Moreover, a process can use function getpid() to retrieve the process ID assigned to this process.

Therefore, after the system call to fork(), a simple test can tell which process is the child. Please note that Unix will make an exact copy of the parent's address space and give it to the child. Therefore, the parent and child processes have separate address spaces.

Code:

#include<stdio.h>

#include<stdlib.h>

#include<sys/types.h>

#include<sys/stat.h>

#include<unistd.h>

#include<errno.h>

int main(int argc, char *argv[])

{

pid_t pid;

pid=fork();

if (pid == 0) {

printf("This is the child process. My pid is %d and my parent's id is %d.\n", getpid(), getppid());

}

else {

   printf("This is the parent process. My pid is %d and my parent's id is %d.\n", getpid(), pid);

}

return 0;

}

Output:

A Java program for Calculator

Program code:


package UdpServer;

import java.awt.*;
import java.awt.event.*;
 
 
public class calci extends Frame
{
 
public boolean setClear=true;
double number, memValue;
char op;
 
String digitButtonText[] = {"7", "8", "9", "4", "5", "6", "1", "2", "3", "0", "+/-", "." };
String operatorButtonText[] = {"/", "sqrt", "*", "%", "-", "1/X", "+", "=" };
String memoryButtonText[] = {"MC", "MR", "MS", "M+" };
String specialButtonText[] = {"Backspc", "C", "CE" };
 
MyDigitButton digitButton[]=new MyDigitButton[digitButtonText.length];
MyOperatorButton operatorButton[]=new MyOperatorButton[operatorButtonText.length];
MyMemoryButton memoryButton[]=new MyMemoryButton[memoryButtonText.length];
MySpecialButton specialButton[]=new MySpecialButton[specialButtonText.length];
 
Label displayLabel=new Label("0",Label.RIGHT);
Label memLabel=new Label(" ",Label.RIGHT);
 
final int FRAME_WIDTH=325,FRAME_HEIGHT=325;
final int HEIGHT=30, WIDTH=30, H_SPACE=10,V_SPACE=10;
final int TOPX=30, TOPY=50;
///////////////////////////
calci(String frameText)//constructor
{
super(frameText);
 
int tempX=TOPX, y=TOPY;
displayLabel.setBounds(tempX,y,240,HEIGHT);
displayLabel.setBackground(Color.BLUE);
displayLabel.setForeground(Color.WHITE);
add(displayLabel);
 
memLabel.setBounds(TOPX,  TOPY+HEIGHT+ V_SPACE,WIDTH, HEIGHT);
add(memLabel);
 
// set Co-ordinates for Memory Buttons
tempX=TOPX;  
y=TOPY+2*(HEIGHT+V_SPACE);
for(int i=0; i<memoryButton.length; i++)
{
memoryButton[i]=new MyMemoryButton(tempX,y,WIDTH,HEIGHT,memoryButtonText[i], this);
memoryButton[i].setForeground(Color.RED);
y+=HEIGHT+V_SPACE;
}
 
//set Co-ordinates for Special Buttons
tempX=TOPX+1*(WIDTH+H_SPACE); y=TOPY+1*(HEIGHT+V_SPACE);
for(int i=0;i<specialButton.length;i++)
{
specialButton[i]=new MySpecialButton(tempX,y,WIDTH*2,HEIGHT,specialButtonText[i], this);
specialButton[i].setForeground(Color.RED);
tempX=tempX+2*WIDTH+H_SPACE;
}
 
//set Co-ordinates for Digit Buttons
int digitX=TOPX+WIDTH+H_SPACE;
int digitY=TOPY+2*(HEIGHT+V_SPACE);
tempX=digitX;  y=digitY;
for(int i=0;i<digitButton.length;i++)
{
digitButton[i]=new MyDigitButton(tempX,y,WIDTH,HEIGHT,digitButtonText[i], this);
digitButton[i].setForeground(Color.BLUE);
tempX+=WIDTH+H_SPACE;
if((i+1)%3==0){tempX=digitX; y+=HEIGHT+V_SPACE;}
}
 
//set Co-ordinates for Operator Buttons
int opsX=digitX+2*(WIDTH+H_SPACE)+H_SPACE;
int opsY=digitY;
tempX=opsX;  y=opsY;
for(int i=0;i<operatorButton.length;i++)
{
tempX+=WIDTH+H_SPACE;
operatorButton[i]=new MyOperatorButton(tempX,y,WIDTH,HEIGHT,operatorButtonText[i], this);
operatorButton[i].setForeground(Color.RED);
if((i+1)%2==0){tempX=opsX; y+=HEIGHT+V_SPACE;}
}
 
addWindowListener(new WindowAdapter()
{
public void windowClosing(WindowEvent ev)
{System.exit(0);}
});
 
setLayout(null);
setSize(FRAME_WIDTH,FRAME_HEIGHT);
setVisible(true);
}
//////////////////////////////////
static String getFormattedText(double temp)
{
String resText=""+temp;
if(resText.lastIndexOf(".0")>0)
    resText=resText.substring(0,resText.length()-2);
return resText;
}
////////////////////////////////////////
public static void main(String []args)
{
new calci("Calculator - JavaTpoint");
}
}
 

 
class MyDigitButton extends Button implements ActionListener
{
calci cl;
 

MyDigitButton(int x,int y, int width,int height,String cap, calci clc)
{
super(cap);
setBounds(x,y,width,height);
this.cl=clc;
this.cl.add(this);
addActionListener(this);
}

static boolean isInString(String s, char ch)
{
for(int i=0; i<s.length();i++) if(s.charAt(i)==ch) return true;
return false;
}

public void actionPerformed(ActionEvent ev)
{
String tempText=((MyDigitButton)ev.getSource()).getLabel();
 
if(tempText.equals("."))
{
 if(cl.setClear)  
    {cl.displayLabel.setText("0.");cl.setClear=false;}
 else if(!isInString(cl.displayLabel.getText(),'.'))
    cl.displayLabel.setText(cl.displayLabel.getText()+".");
 return;
}
 
int index=0;
try{
        index=Integer.parseInt(tempText);
    }catch(NumberFormatException e){return;}
 
if (index==0 && cl.displayLabel.getText().equals("0")) return;
 
if(cl.setClear)
            {cl.displayLabel.setText(""+index);cl.setClear=false;}
else
    cl.displayLabel.setText(cl.displayLabel.getText()+index);
}//actionPerformed
}//class defination
 
/********************************************/
 
class MyOperatorButton extends Button implements ActionListener
{
calci cl;
 
MyOperatorButton(int x,int y, int width,int height,String cap, calci clc)
{
super(cap);
setBounds(x,y,width,height);
this.cl=clc;
this.cl.add(this);
addActionListener(this);
}
 
public void actionPerformed(ActionEvent ev)
{
String opText=((MyOperatorButton)ev.getSource()).getLabel();
 
cl.setClear=true;
double temp=Double.parseDouble(cl.displayLabel.getText());
 
if(opText.equals("1/x"))
    {
    try
        {double tempd=1/(double)temp;
        cl.displayLabel.setText(calci.getFormattedText(tempd));}
    catch(ArithmeticException excp)
                        {cl.displayLabel.setText("Divide by 0.");}
    return;
    }
if(opText.equals("sqrt"))
    {
    try
        {double tempd=Math.sqrt(temp);
        cl.displayLabel.setText(calci.getFormattedText(tempd));}
            catch(ArithmeticException excp)
                    {cl.displayLabel.setText("Divide by 0.");}
    return;
    }
if(!opText.equals("="))
    {
    cl.number=temp;
    cl.op=opText.charAt(0);
    return;
    }
// process = button pressed
switch(cl.op)
{
case '+':
    temp+=cl.number;break;
case '-':
    temp=cl.number-temp;break;
case '*':
    temp*=cl.number;break;
case '%':
    try{temp=cl.number%temp;}
    catch(ArithmeticException excp)
        {cl.displayLabel.setText("Divide by 0."); return;}
    break;
case '/':
    try{temp=cl.number/temp;}
        catch(ArithmeticException excp)
                {cl.displayLabel.setText("Divide by 0."); return;}
    break;
}//switch
 
cl.displayLabel.setText(calci.getFormattedText(temp));
//cl.number=temp;
}//actionPerformed
}//class
 
/****************************************/
 
class MyMemoryButton extends Button implements ActionListener
{
calci cl;
 

MyMemoryButton(int x,int y, int width,int height,String cap, calci clc)
{
super(cap);
setBounds(x,y,width,height);
this.cl=clc;
this.cl.add(this);
addActionListener(this);
}

public void actionPerformed(ActionEvent ev)
{
char memop=((MyMemoryButton)ev.getSource()).getLabel().charAt(1);
 
cl.setClear=true;
double temp=Double.parseDouble(cl.displayLabel.getText());
 
switch(memop)
{
case 'C':  
    cl.memLabel.setText(" ");cl.memValue=0.0;break;
case 'R':  
    cl.displayLabel.setText(calci.getFormattedText(cl.memValue));break;
case 'S':
    cl.memValue=0.0;
case '+':  
    cl.memValue+=Double.parseDouble(cl.displayLabel.getText());
    if(cl.displayLabel.getText().equals("0") || cl.displayLabel.getText().equals("0.0")  )
        cl.memLabel.setText(" ");
    else  
        cl.memLabel.setText("M");    
    break;
}//switch
}//actionPerformed
}//class
 
/*****************************************/
 
class MySpecialButton extends Button implements ActionListener
{
calci cl;
 
MySpecialButton(int x,int y, int width,int height,String cap, calci clc)
{
super(cap);
setBounds(x,y,width,height);
this.cl=clc;
this.cl.add(this);
addActionListener(this);
}
//////////////////////
static String backSpace(String s)
{
String Res="";
for(int i=0; i<s.length()-1; i++) Res+=s.charAt(i);
return Res;
}
 
//////////////////////////////////////////////////////////
public void actionPerformed(ActionEvent ev)
{
String opText=((MySpecialButton)ev.getSource()).getLabel();
//check for backspace button
if(opText.equals("Backspc"))
{
String tempText=backSpace(cl.displayLabel.getText());
if(tempText.equals(""))  
    cl.displayLabel.setText("0");
else  
    cl.displayLabel.setText(tempText);
return;
}
//check for "C" button i.e. Reset
if(opText.equals("C"))  
{
cl.number=0.0; cl.op=' '; cl.memValue=0.0;
cl.memLabel.setText(" ");
}
 
//it must be CE button pressed
cl.displayLabel.setText("0");cl.setClear=true;
}//actionPerformed
}//


Output

JAVA TCP program to create a simple Calculator.

Client Side Code:

package serverclient1;
import java.util.*;
import java.io.*;
import java.net.*;

public class ClientCalci {
    public static void main(String arg[]){
        try{
                             Socket s=new Socket( "localhost",1234);
                             Scanner sc=new Scanner(System.in);
                             DataOutputStream dos=new DataOutputStream(s.getOutputStream());
                             DataInputStream din=new DataInputStream(s.getInputStream());
                             System.out.print("Enter your choice: ");
                             int c=sc.nextInt();
                             dos.write(c);
                             System.out.println("Enter Two Number : ");
                             int a=sc.nextInt();
                             dos.write(a);
                             int b=sc.nextInt();
                             dos.write(b);
                             int res=din.readInt();
                             System.out.println("Result is:" +res);
                           
}
                        catch(Exception e){}
    }

}

Server Side Code :

package serverclient1;

    

    

import java.io.*;

import java.lang.*;

import java.net.*;

public class ServerCalci{

public static void main(String arg[]){

try{

int a,b,c,d;

int ch;

ServerSocket ss = new ServerSocket(1234);

while(true){

Socket s = ss.accept();

BufferedReader bin=new BufferedReader(new InputStreamReader(s.getInputStream()));

DataOutputStream dout=new DataOutputStream(s.getOutputStream());

 System.out.print("1. Addition\n");

             System.out.print("2. Subtraction\n");

             System.out.print("3. Multiplication\n");

            System.out.print("4. Division\n");

             System.out.print("5. Exit\n\n");

ch=bin.read();

switch(ch)

            {

                    case 1 : 

                    a = bin.read();

                    b = bin.read();

                    c = a + b;

                    System.out.print("Result = " + c);

dout.writeInt(c);  

                  break;

                case 2 : 

                    a = bin.read();

                    b = bin.read();

                    c = a - b;

                    System.out.print("Result = " +c);

dout.writeInt(c); 

break;

                case 3 : 

                    a = bin.read();

                    b = bin.read();

                    c = a * b;

                    System.out.print("Result = " +c);

dout.writeInt(c); 

                    break;

                case 4 : 

                    a = bin.read();

                    b = bin.read();

                    c = a / b;

                    System.out.print("Result = " +c);

dout.writeInt(c);                     

break;

                case 5 : System.exit(0);

                    break;

                default : System.out.print("Wrong Choice!!!");

                    break;

            }

}

}

catch(Exception e){}

}

}

Output

For Addition

For Subtraction

 
 


For Multiplication
 
 

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Dynamic Method Dispatch

Method overriding forms the basis for one of Java’s most powerful concepts: dynamic method dispatch. Dynamic method dispatch is the mechanism by which a call to an overridden method is resolved at run time, rather than compile time. Dynamic method dispatch is important because this is how Java implements run-time polymorphism.

·       By restating an important principle: a super class reference variable can refer to a subclass object. Java uses this fact to resolve calls to overridden methods at run time. Here is how. When an overridden method is called through a super class reference, Java determines which version of that method to execute based upon the type of the object being referred to at the time the call occurs. Thus, this determination is made at run time. When different types of objects are referred to, different versions of an overridden method will be called.

·       In other words, it is the type of the object being referred to (not the type of the reference variable) that determines which version of an overridden method will be executed. Therefore, if a superclass contains a method that is overridden by a subclass, then when different types of objects are referred to through a superclass reference variable, different versions of the method are executed.

·        Here is an example that illustrates dynamic method dispatch:

// Dynamic Method Dispatch

 class A {

  void callme(){

   System.out.println("Inside A's callme method");

   }

 } 

class B extends A {// override callme()

  void callme() {

   System.out.println("Inside B's callme method");

  }

 } 

class C extends A {  // override callme()

  void callme() {

  System.out.println("Inside C's callme method");

   }

 } 

class Dispatch {

  public static void main(String args[]) {

   A a = new A(); // object of type A

   B b = new B(); // object of type B

   C c = new C(); // object of type C 

  A r; // obtain a reference of type A

   r = a; // r refers to an A object

   r.callme(); // calls A's version of callme

   r = b; // r refers to a B object

   r.callme(); // calls B's version of callme

   r = c; // r refers to a C object

   r.callme(); // calls C's version of callme

   }

 }

   OUTPUT