Create a Simple Calculator - V1

package ArithOp;

public class Common{
    protected int x,y;
    public Common(){

    }
    public Common(int a, int b){
        x = a;
        y = b;
    }
}


package ArithOp;

public class Addition extends Common{
    public Addition(){
        super();
    }
    public Addition(int x, int y){
        super(x,y);
    }
    public void res(){
        System.out.println("The addition is: " + (x+y));
    }
}



package ArithOp;

public class Subtraction extends Common{
    public Subtraction(){
        super();
    }
    public Subtraction(int x, int y){
        super(x,y);
    }
    public void res(){
        System.out.println("The Subtraction is: " + (super.x-super.y));
    }
}


package ArithOp;

public class Multiplication extends Common{
    public Multiplication(){
        super();
    }
    public Multiplication(int x, int y){
        super(x,y);
    }
    public void res(){
        System.out.println("The Multiplication is: " + (x*y));
    }
}



package ArithOp;

public class Division extends Common{
    public Division(){
        super();
    }
    public Division(int x, int y){
        super(x,y);
    }
    public void res(){
        try{
            int z = x/y;
            System.out.println("The Division is: " + z);
        }catch(Exception e){
            System.out.println("Cant Divide by Zero " + e );
        }
    }
}

package simple_calculator;

import java.util.Scanner;
import java.io.*;
import ArithOp.*;

public class Main{
    public static void main(String args[]) throws IOException{
        Scanner cin = new Scanner(System.in);
        int x,y;
        while(cin.hasNext()){
            x = cin.nextInt();
            String as = cin.next();
            y = cin.nextInt();

            if(as.equals("+")){
                Addition a = new Addition(x,y);
                a.res();
            }
            else if(as.equals("-")){
                Subtraction s = new Subtraction(x,y);
                s.res();
            }
            else if(as.equals("*")){
                Multiplication m = new Multiplication(x,y);
                m.res();
            }
            else if(as.equals("/")){
                Division d = new Division(x,y);
                d.res();
            }
        }
    }
}

Vector Operation

package vec_operation;

import java.util.Vector;
import java.util.Iterator;
import java.util.Collections;
import java.util.Enumeration;

public class Main{
    public static void main(String args[]){
        Vector  v = new Vector();
        for(int i=0;i<10;i++) v.add(i);
        //Size of vector
        System.out.println(v.size());
        //Empty or not
        System.out.println(v.isEmpty());
        //iterating element
        Iterator it = v.iterator();
        while(it.hasNext()){
            System.out.println(it.next());
        }
        //vector reverse
        Collections.reverse(v);
        System.out.println(v);
        //sorting vector
        Collections.sort(v);
        System.out.println(v);
        //decalaring antoher vector
        Vector v1 = new Vector();
        for(int i=0;i<3;i++) v1.addElement("I love you");
        //printing elements
        Enumeration e = v1.elements();
        while(e.hasMoreElements()){
            System.out.println(e.nextElement());
        }
    }
}

Using "this" keyword in Constructors

package thisss;

public class Triangle{
    double x,y;
    Triangle(){
        this(0,0);
    }
    Triangle(double x){
        this(x,x);
    }
    Triangle(double x, double y){
        this.x=x;
        this.y=y;
    }
    void area(){
        System.out.println("The area of the triangle is: " + (x*y)/2.0);
    }
}


package thisss;

public class Main{
    public static void main(String args[]){
        Triangle t = new Triangle();
        Triangle tri = new Triangle(3);
        Triangle tri2 = new Triangle(3,2);
        t.area();
        tri.area();
        tri2.area();
     }
}

Reading and writing on a File

package file_read;

import java.io.FileReader;
import java.io.BufferedReader;
import java.io.FileWriter;

public class Main{
    public String file_read(String name){
        String line="", temp="";
        try{
            FileReader fin = new FileReader(name);
            BufferedReader br = new BufferedReader(fin);
            while((line=br.readLine())!=null){
                temp+= line + "\n";
            }
            fin.close();
            return temp;
        }catch(Exception e){
            System.out.println("Exception Occured" + e);
        }
        finally{
            return temp;
        }
    }

    public void file_write(String name, int mode, String msg){
        String msgVar = "";
        if(mode==0) msgVar = msg;
        else if(mode==1) msgVar = file_read(name)+ msg + "\n";
        try{
            FileWriter fout = new FileWriter(name);
            fout.write(msgVar);
            fout.close();
        }catch(Exception e){
            System.out.println("File read Problem " + e );
        }
    }
    public static void main(String args[]){
        Main mno = new Main();
        String file_name = "C:/myfile.txt";
        mno.file_write(file_name, 1, "I am in great Confusion");
        String read = mno.file_read(file_name);
        System.out.println(read);
    }
}

Extending Interface

package extending_interface;

public interface ShowMsg1{
    void Msg1();
}


package extending_interface;

public interface ShowMsg2 extends ShowMsg1{
    void Msg2();
}


package extending_interface;

public class Show implements ShowMsg2{
    public void Msg1(){
        System.out.println("This is Msg1");
    }
    public void Msg2(){
        System.out.println("This is Msg2");
    }
}


package extending_interface;

public class Main{
    public static void main(String args[]){
        Show sw = new Show();
        sw.Msg1();
        sw.Msg2();
    }
}

Using Final to avoid inheritance

package final_inheritance;

public final class A{
    A(){
        System.out.println("This is class A");
    }
}


package final_inheritance;

public class B extends A{ //This is an ERROR
    //Cant be inherited
}



package final_inheritance;

public class Main{
    public static void main(String args[]){
            .......
    }
}

Find the odd number

import java.io.FileReader;
import java.io.BufferedReader;
import java.io.FileWriter;
import java.util.StringTokenizer;

public class Main{
    public String file_read(String name){
        String line="",temp="";
        try{
            FileReader fin = new FileReader(name);
            BufferedReader br = new BufferedReader(fin);
            while((line=br.readLine())!=null){
                temp+= line + "\n";
            }
            fin.close();
            return temp;
        }catch(Exception e){
            System.out.println("File reading problem " + e);
        }finally{
            return temp;
        }


    }
    public void file_write(String name, int mode, String msg){
        String msgVar = "";
        if(mode==0) msgVar = msg;
        else if(mode==1) msgVar = file_read(name) + msg + "\n";
        try{
            FileWriter fout = new FileWriter(name);
            fout.write(msgVar);
            fout.close();
        }catch(Exception e){
            System.out.println("File read Problem "  + e);
        }
    }
    public static void main(String args[]){
            Main mno = new Main();
            String file_name = "C:/myfile.txt";
            mno.file_write(file_name, 0 , "1,2,3,4,5,16,2,8");
            int count = 0;
            String temp = mno.file_read(file_name);
            StringTokenizer st = new StringTokenizer(temp,",");
            while(st.hasMoreTokens()){
                String t = st.nextToken().trim();
                int x = Integer.parseInt(t);
                if(x%2==0) count++;
            }
            System.out.println(count);

    }
}