Learn Java Part 9

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Learn Java Part 9 from Gurpreet singh

Learn Java Part 8

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Learn Java Part 8 from Gurpreet singh

How to get an alert when anyone logs into your Facebook account from a new device or browser?

Follow these steps:

• Log In into your Facebook account and goto Settings.

• Then Jump to “Security Settings” Tab and You can see a Login “Login Alerts” and Click on “Edit”.

• Check the Get notifications

• If you want to receive emails alerts then check it

• If you want to receive text messages alerts then check it

• Click Save Changes and enter your current password and click Submit

• Your changes will be saved and now will get an alert when anyone logs into your Facebook account from a new device or browser

Program to calculate how many times a word occurs in a given string in just one line

//Program to calculate how many times a word occurs in a given string in just one line

import java.io.*;  //for IOException, BufferedReader, InputStreamReader
class CountWord
{
  public static void main(String args[]) throws IOException
  {
     System.out.println("Enter the string: ");
     BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
     String s=br.readLine();  //Gets a string from user
     System.out.println("Enter the word to search for: ");
     String word=br.readLine();  //Gets a string from user

     int count=(s.length()-s.replace(word+"", "").length())/word.length();     

   System.out.println(word+" occurs in given string for: "+count+" times");
  }
}

Program to reverse each word of a given string

//Program to reverse each word of a given string

import java.io.*;  //for IOException, BufferedReader, InputStreamReader
import java.util.*;  //for StringBuffer
public class WordReverse {
    public static void main(String[] args)throws IOException
    {
    BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
    System.out.println("Enter the string:");
    String str=br.readLine();
    StringTokenizer st=new StringTokenizer(str);
    String temp="";
    while(st.hasMoreTokens())
    {
        temp=temp+new StringBuffer(st.nextToken()).reverse().toString()+" ";
    }
        System.out.println("Reversed String is:");
        System.out.println(temp);
    }   
}

Output:

Enter the string:

Hello this is GsbProgramming

Reversed String is:

olleH siht si gnimmargorPbsG 

Learn Java Part 7

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Learn Java Part 7 from Gurpreet singh

Program to calculate how many times a word occurs in a given string

//Program to calculate how many times a word occurs in a given string

import java.io.*;  //for IOException, BufferedReader, InputStreamReader
class CountWord
{
  public static void main(String args[]) throws IOException
  {
     System.out.println("Enter the string: ");
     BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
     String s=br.readLine();  //Gets a string from user
     System.out.println("Enter the word to search for: ");
     String word=br.readLine();  //Gets a string from user

     int count=0,pos=0;
     while(true)
     {
        pos=s.indexOf(word,pos);
        if(pos==-1)
            break;
        else
        {
            count++;
            pos++;
        }
      }

   System.out.println(word+" occurs in given string for: "+count+" times");
  }
}

Program to calculate the frequency of each character in given String

//Program to calculate the frequency of each character in given String

import java.io.*; //for IOExecption, BufferedReader, InputStreamReader
class CharacterFrequency
{
  public static void main(String args[]) throws IOException
  {
     System.out.println("Enter the string: ");
     BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
     String s=br.readLine(); //gets a string from user
     String temp=s;
     System.out.println("\nFollowing are the characters in string");
    
     while(temp.length()!=0)
     {
        char ch=temp.charAt(0);
        int count=0;
        for(int i=0;i<temp.length();i++)
          if(temp.charAt(i)==ch)
            count++;
        System.out.println(ch+": "+count);
     temp=temp.replace(ch+"","");  //replaces the current character with empty string
     }
  }
}

Learn Java Part 6

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Learn Java Part 6 from Gurpreet singh

Printing different patterns of Stars with the help of nested for loop

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Stars from Gurpreet singh

Naming, Compiling and Running Java Files Containing More Than One Class Definitions

Today we will see how to name, compile and running java files containing more than one class definitions.



1). Consider the following program.

class ClassOne {      public static void main(String[] args)      {          ClassTwo.methodOfClassTwo();      } } class ClassTwo {      static void methodOfClassTwo()      {          System.out.println("From Class Two");      } }

Naming : You can save this program with any name. It can be ClassOne.java or it can be ClassTwo.java or it can be anything.java.



Compile : You have to compile this program with the name you have given like >javac ClassOne.java or >javac ClassTwo.java or >javac anything.java.

When you compile a java file, the number of .class files
generated will be equal to number of class definitions in it. i.e If a
java file has one class definition, one .class file will be generated.
If it has two class definitions, two .class file will be generated and
so on.

Running : That means for the above program, two .class files will be generated. Then which one to run? is it >java ClassOne or is it >java ClassTwo…..    It must be >java ClassOne, because execution of any java program start with main() method. If you try to run >java ClassTwo, you will get an error: Main method not found in class ClassTwo, please define the main method as public static void main(String[] args).



2). Now consider same example with litte modification, just declare ClassOne as public.

public class ClassOne {      public static void main(String[] args)      {           ClassTwo.methodOfClassTwo();      } } class ClassTwo {      static void methodOfClassTwo()      {           System.out.println("From Class Two");      } }

Naming : The name of above java file must be and only
“ClassOne.java”. You can’t give any other name. If you give any other
name you will get compile time error : class ClassOne is public, should be declared in a file named ClassOne.java.

Compile : Only one name is allowed here so you have to compile with that name i.e >javac ClassOne.java.

Running : That must be >java ClassOne. because this is only class that has main() method.





3). Now make little more modifications to the program. Declare ClassTwo as public and ClassOne as default.

class ClassOne {      public static void main(String[] args)      {           ClassTwo.methodOfClassTwo();      } } public class ClassTwo {      static void methodOfClassTwo()      {           System.out.println("From Class Two");      } }

Naming : You have to save this file with name as “ClassTwo.java”. If you give any other name you will get compile time error becuase ClassTwo is public.

Compile : It must be >javac ClassTwo.java.

Running : You must name this program as ClassTwo.java, you must compile this program as >javac ClassTwo.java but you have to run it as >java ClassOne not as >java ClassTwo. Because only ClassOne has main() method. ClassTwo doesn’t have main() method. If you run it as >java ClassTwo, you will get run time error : Main method not found in class ClassTwo, please define the main method as public static void main(String[] args).



4). Now make little more modifications to the program. Declare both the classes as public.

public class ClassOne {      public static void main(String[] args)      {           ClassTwo.methodOfClassTwo();      } } public class ClassTwo {      static void methodOfClassTwo()      {           System.out.println("From Class Two");      } }

Naming : Whatever you give the name, whether it is ClassOne.java or
ClassTwo.java or anything.java,  you will get compile time error.
Because One java file should contain only one or zero public class. It should not contain more than one public class.



5) Look at the following program.

class ClassOne {      public static void main(String[] args)      {           System.out.println("From Class One");      } } class ClassTwo {      public static void main(String[] args)      {           System.out.println("From Class Two");      } }

Naming : You can save this program with any name. It can be ClassOne.java or it can be ClassTwo.java or it can be anything.java as there is no public class.



Compile : You have to compile this program with the name you have given i.e >javac ClassOne.java or >javac ClassTwo.java or >javac anything.java.

Running : Notice that both the classes have main() method. You can run both the classes with their name. i.e  If you trigger >java ClassOne, you will get From Class One as output. If you trigger >java ClassTwo, you will get From Class Two as output.

Changing default directory of CMD

To change default directory of CMD follow these steps:

• Open CMD and type regedit and press Enter

• Registry Editor will open. 

• Navigate to the key HKEY_CURRENT_USER \ Software \ Microsoft \ Command Processor from left side. Now Right click on right panel. Select New, then String Value

• Name it as Autorun

• Now double click Autorun and type cd /d "New Path" in Value Data textbox. For example if you want that whenever you open CMD the default path will be E:\GSBPROGRAMMING then you will type as: cd /d E:\GSBPROGRAMMING then click OK and close the Registory Editor and also CMD.

• Now open CMD again and it will open with new default directory everytime

Learn Java Part 5

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Learn Java Part 5 from Gurpreet singh

Learn Java Part 4

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Learn Java Part 4 from Gurpreet singh