Author: allaboutbasic

Sometimes we may need to collect data or information from database to HashMap in java. Here I have given an example to show how to collect data from database and then  use it as key of HashMap.
HashMap, you may know that, takes two values, first one is KEY Value ( must be Unique) and the second one is Actual Value. Using that key value in HashMap you may search that actual value you entered.
For example:
if ( hmData.get(itMat1)==”1″)
     
     {
      row.add(“Yes”);
     }

In the given example   hmData.put(itMat,”1″);   itMat is the  key value  and regarding this KeyValue I have entered “1” as the actual value to  use in my software.

Here is the sample code to collect or retrieve data from database to HashMap:

HashMap hmData=new HashMap();
   Connection conNew =  PuConnection.DB_Connection();
   String newsql = “select distinct item_no,mat_no from a_nr_allocate_temp”;
   try
   {
   Statement stmtnew = conNew.createStatement();
   ResultSet rsNew = stmtnew.executeQuery(newsql);
   int i=1;
   while(rsNew.next()){
    String itemNo=rsNew.getString(“item_no”);
    String matNo=rsNew.getString(“mat_no”);
    String itMat= itemNo+matNo;
    
    hmData.put(itMat,”1″);
    System.out.println(“Inside Hashmap:for itMat”+ itMat+”Hashmap:value is:”+hmData.get(itMat));
    
    }
   rsNew.close();
   stmtnew.close();
   conNew.close();
   }
   catch(Exception e){}

In String manipulation sometimes we may need to break the string into each separate or individual character.

In java we can do it easily using  toCharArray() function.

In the given example, string   “Java Programming ”  is broken down into characters where you can see that the length of that string is 16 (including the space between  “Java” and “Programming”) and the whole string is broken into each individual character , where we have stored that characters into  an array.

Here is the code to convert  string into array:

class StringBreaker

{

StringBreaker()

{

String s=”Java Programming”;

char[] allchars=new char[s.length()];  

allchars = s.toCharArray();

System.out.println(“****************************”);

System.out.println(“\n”);

 System.out.println(“Length of S:”+s.length());

System.out.println(“\n”);

 for (int n=0; n<s.length(); n++)

{

try

            {

            System.out.println(“Character::”+(n+1)+”::”+allchars[n]);

            }

catch(Exception e){}

              }

 System.out.println(“\n”);

 System.out.println(“****************************”);

}

public static void main(String args[])

{

StringBreaker test=new StringBreaker();

}

}

OUTPUT:

Sometimes we may need in java programming to pass the value of array in another function.

Here I have given an example about the procedure of passing an array to a function.

Also, here I have shown how to find out the length of an array and how to retrieve or get the value of the array after passing it to another function.

This tutorial will help you to understand the basic of array and how to declare array in java.

Code:

 class ArrayPassing

{

 public static void checking(String[] u)

  {

 System.out.println(“\n”);

System.out.println(“****************************************”);

  System.out.println(“Array is entered into Checking function”);

  System.out.println(“Array Length:”+u.length);

  System.out.println(“Third index value is:”+u[2]);

  System.out.println(“\n”);

  System.out.println(“****************************************”);

  }

         public static void main(String args[])

                        {

                                    String[] d;

                                    d = new String[3];

                                    d[0]=”1″;

                                    d[1]=”2″;

                                    d[2]=”5″;

                                     checking(d);

                                     }

}

OUTPUT:

I have discussed about how to take input from user in runtime from command line here.

Here I will try to give a simple example regarding this.

In this example, our program will take total student number and total subject as input, then it will take input of each subject number. After calculating the average number of total subject, if any student gets less than 40 it will show that student is failed and if any student gets more than 40 that student is passed.

Here is the given Code:

import java.io.*;

class student

{

public static void main(String args[])

{

String inputa;

int num_std;        // Total Number of Student

int sub_std;        // Total Subject of Student

System.out.println(“************************************”);

System.out.println(“\n”);

System.out.println(“Enter the Total Number of Students:”);

System.out.println(“\n”);

BufferedReader br=new BufferedReader(new InputStreamReader(System.in));

try{

inputa=br.readLine();

num_std=Integer.parseInt(inputa);

System.out.println(“Enter the Total Subject of Student:”);

System.out.println(“\n”);

inputa=br.readLine();

sub_std= Integer.parseInt(inputa);

int i=0;

int j=0;

int z=0;

System.out.println(“\n”);

for (i=1;i<=num_std;i++)

{

System.out.println(“Enter Student  :” +i+” :Subject Number:”);

System.out.println(“\n”);

for (j=1;j<=sub_std;j++)

{

inputa= br.readLine();

z= z+Integer.parseInt(inputa);

if(j==sub_std)

{

System.out.println(“Student:”+i+”Total Number:”+z);

int om=(z)/sub_std;

if(om<40)

{

System.out.println(“Student:”+i+”fails”);

System.out.println(“Student  :”+i+” :  Average Number:”+om);

om=0;

z=0;

}

else

{

System.out.println(“Student  :”+i+” :  passed”);

System.out.println(“Student  :”+i+” :  Average Number:”+om);

om=0;

z=0;

}

}

} //End of student  subject loop

} //End of student num loop

System.out.println(“\n”);

System.out.println(“************************************”);

}

catch(IOException e)

{}

}

}

OUTPUT:

Suppose you are doing your coding in java (let you are running your program from command prompt of your desktop) and you need to take input from user in command line or command prompt while  user  run (actually runtime input) your program.

Now I will show you how to take user input from command prompt or command line in java.

Here I have used BufferedReader  and readLine()  to take input from user in command line/ command prompt while the program was running or  simply in run time.

In the example below  br.readLine() takes  input as String, in the next line we have parsed or convert that String into integer.

Code:

import java.io.*;

public class CmdLineInput

{

CmdLineInput()

{

String inputa;

int num_std;

BufferedReader br=new BufferedReader(new InputStreamReader(System.in));

try{

System.out.println(“Enter the number of Students:”);

inputa=br.readLine();

num_std=Integer.parseInt(inputa);

System.out.println(“Number of Students:”+num_std);

   }

 catch(Exception e){}

   }

public static void main(String args[])

{

CmdLineInput takeinput=new CmdLineInput();

}

}

OUTPUT:

Static Method:

I have discussed  Static Variable before,  you can check it from here.

Now I am going to discuss about Static Method.  It is also called Class Method.

In general we can say that methods declared with the keyword Static as modifier are called Static Methods or Class Methods.

Static Method in Java is that type of method which belongs to a class rather than an object of a class. Static Methods are invoked without reference to a particular instance (object) of a class.

So, anyone can invoke a Static Method without having to instantiate an object.

Important Notes / Features:

1. In Static Method, you can only manipulate variables that are declared as static, not other variables. It is because, something that is common to a class cannot refer to things that are  specific to an object.

 2. Static Method can call only other Static Methods.

3. Static Method cannot reference to the current object using super or this keyword.

 *** static means that it cannot be changed

Code:

public class StaticMethod

{

static int value=10;

StaticMethod()

{

test2 test =new test2();

}

              public static int getValue()

                        {

                        return value;

                        }

                        public int againgetValue()

                        {

                        return value;

                        }

public class test2

{

test2()

{

int getvalue= StaticMethod.getValue();

System.out.println(“Test2  calling the value StaticMethod.getValue(): “+getvalue); //Correct

//int setvalue= StaticMethod.againgetValue();  ****

//System.out.println(“test2  calling the value  StaticMethod.againgetValue() “+setvalue); **

}

}

public static void main(String args[])

{

StaticMethod test=new StaticMethod();

}

}

*** These 2 lines  will give error message as Instant Method cant be call in this way.

OUTPUT:

Test2  calling the value StaticMethod.getValue(): 10

By default Java Programs(GUI based)actually starts/Open  in the side of the desktop.  IF you want your java program/software (where GUI such as JFrame or JPanel is used) to open by default in the middle of the desktop then it’s for you.

Here I have given the code which will help you to open your java (JFrame window) in the middle of the desktop.

Whatever the resolution of your desktop monitor has, this code will help you to open your desire java written software exactly in the middle of the monitor.

Code:

import java.awt.*;

import javax.swing.*;

public class middlePosition extends JFrame

{

private Toolkit  toolkit;

                                                public middlePosition()

                                                {

                                                JPanel panel=new JPanel();

                                                getContentPane().add(panel);

                                                panel.setLayout(null);

                                                setSize(500,500);

                                                setTitle(“Set JFrame Window in the middle of the Desktop”);

                                                setDefaultCloseOperation(EXIT_ON_CLOSE);

                                                toolkit=getToolkit();

                                                Dimension size=toolkit.getScreenSize();

                                                setLocation(size.width/2-getWidth()/2, size.height/2-getHeight()/2);

                                                }

                        public static void main(String args[])

                        {

                        middlePosition x=new middlePosition();

                        x.setVisible(true);

                        }

}

OUTPUT:

How to show image on JLabel:

If we need to show image as a background of a JLabel, then we can easily show it by using ImageIcon and then by setting that  ImageIcon to the JLabel.

Download this project from:

http://www.ziddu.com/download/12618536/jLabelImgIcon.zip.html

I have uploaded the project  and I used  NetBeans IDE 5.0 (You can use latest version) and JDK 1.4.2

I am not giving the whole code here, just I am mentioning the Core Portion of the code. Better you download the project and Run it in your computer.

Code:

import javax.swing.*;

import java.awt.image.BufferedImage;

public class jLabelImgIcon extends javax.swing.JFrame {

private void myInit()

{

 ImageIcon icon = new ImageIcon(“C:\\myworkspace\\sample.png”);

 icon = new ImageIcon(icon.getImage().getScaledInstance(100, 100, BufferedImage.SCALE_SMOOTH));

 jLabel1.setIcon(icon);     

    }

——————

—————

}

 OutPut:

In the output Image is viewing on JLabel  using ImageIcon and jLabel1.setIcon.

About  Static Class:

Static Class is that class in Java for which we don’t need to create any Object.

Though we can create an object of a static class  but it is meaningless, we can use the members and methods of Static Class without creating an Object . The variables and methods can be used by calling them using class name only

Some Important Notes:

** A static nested class uses the instance variables (not static variables) / methods declared or defined in its enclosing class only by using an object reference.  

Code:

public class StaticVariable1

{

static int demo=0;

 StaticVariable1()

{

NonStaticClass demo1=new NonStaticClass();

System.out.println(“Before Value Change in NonStaticClass i=”+demo1.getValue());

demo1.i=10;

System.out.println(“After Value Change in NonStaticClass i=”+demo1.getValue());

}

static class StaticClass

{

static int i=0;

static int j;

}

public class NonStaticClass

{

int i;

int j;

public int getValue()

{

return i;

}

}

public static void main(String[] args)

{

System.out.println(“Before Value Change in StaticClass i=”+StaticClass.i);

StaticClass.i=10;  // No need to Create Object to initialize value of variable i in StaticClass

System.out.println(“After Value Change in StaticClass i=”+StaticClass.i);

//NonStaticClass.i=10; *** check below

StaticVariable1 demo=new StaticVariable1(); 

}

}

** It will create error   non-static variable i cannot be referenced from a static Context NonStaticClass.i=10;

                          ^

OUTPUT: