We
are doing programming with java some important points to be remember
The projects having several
classes if you want the data of the one class to another you simply create
destination class with the constructor(what are the arguments or data or text
field contents) in the source class after the present class visibility is set to false
Source class{………..
destination d=destination
(JTextFeild.getText();Integer.parseInt(JTextField.getText());
…this
is in the form from text to integer for ex:- no of fields in the text field
here String but in the destination you use that as depending on that number of
the label fields or text fields you want to create you have to convert and pass this nubet to
the for loop
in
the for loop depending on you can create specified number of the text fields
and labels combo boxes and also set their bounds and all put together in single
take we can add to the content pane without adding manually while creating combo boxes or textboxes you remember
you have e to use one static array for storing the label or text what ever it
may be and the array of pointers I.e.
not
only creating the memory for the array for storing the names of the labels or text
fields or combo boxes but indidually that buttons or contents of the array you indidually allot
memory
here
the program contains 1)login page implementation for this another class to
call login page ,after login 4)another class design to implement to ask which table in
the database and also how many fields to store and their data types
also you can select form the combo box then you have the potations in this
frame clear or store or retrive or delegate like …
.
Another
frame is to be implement for the displaying of the database and another 2
frames depending on your requirement aspects and also one point to remember you
are implementing the so many classes in the same program or complex programs
after writing few lines then immediately compile for error handling other wise
screen will fill with full of errors by scrolling it is too difficult for rectification
like adding of the buttons or components after designed to the content pane and
for setLayout(null); setting the boundaries for the items ,actionlisteners ,setbackgrounds and foregrounds
and here addItem(); here setEchochar
not work to fill login page with **** but insetd here we can use the PasswordFill()
while some
time you will forget the implementation of the action Listener to the frame
,window listener depending the application(
this ) action listener to the
buttons and textfields form the text obtain getText(); form the method
itemStateChanged
actionPerformed()
from this getActionCommand(); to obtain which button is activated and what is
its content of the button or label
JFrame.EXIT_ON_CLOSE for the closing of
a frame
And in the above program
before display you have to implement to another FRAME which contain the class
for connecting instructions to the data base
While writing programs mostly
use constructor
implementation for default execution and you want to use the variables
in all methods then you declare them as private section which is global to all methods
Points to
be remember while doing with database programming
JPasswordField
pf=new JPasswordField() ;here
this displays the ‘*’ symbols for each character by deafult
pf.setEchoChar(‘#’); here we are specifying the # symbol while typing the
password
operator.addSeparator(); it
will separates the menu items with line
if we want to add the item to
the menubar c.add(); in swings
concept but in the frame format c.addItem();
by using this we setbounds to
the items as we like where we want to place locations
but serially we add for that
java provides one class setJMenuBar(mb);
here are 5 types of the error message provides the java and their
corresponding symbols
error message
question message
1.information message no
symbol arguments
Table,message,WindowTitle OK button only
2.inputdailogbox it contains
on dialog box for inputting and it will returns the inputted message
StringFormat and the label for
meesage,OK,CANCEL buttons and TextField();
it takes arguments as
NULL,CENTER,Table Created Sucessfully for display message WINDOW TITLE
(for errormessage or
dialog window or any informationWindow for that name and corresponding symbol)
getColoumnCount();
getColoumnLabel(i); Array
getColoumnType(); this is an integer value
getColoumnTypeNames(); this return the number1,varchar2,…….but not return
the data type size
in oracle while reading the
string we place it in the ‘ ’
in the table how many fields
obtain from METADATA class
for example rm.getColoumnName(i)+”===è”+rm.getColoumnNameType();
Class selectdemo
{
public static void
main(String args[])
{
try
{…………………………………….
ResultSet rs=s.executeQuery(“select *from
student”); when we exeuate this
statement not contain the coloumn names these are also retrived by the same
statement but stored in a separate class the below given
ResultSetMetaData rm=rs.getMetaData();// this class
maintains the howmany coloumns and their names in the array of Strings
format getColoumnCount,getColoumnLabel
byspecing in the forloop we obtain that metadata and also one more important
thing is why this data maintain separately of the coloumn names one way is data
abstraction by seeing this MetaData every one easily can understand instead the
only designer
Int col=rm.getColoumnCount();
For(int i=1;i<=col;i++)
System.out.println(rm.getColoumnLabel(i)+”\t”);
While(rs.next())
{
rs.close(); c.close()it is better after the completion of the operations to close it not
affects the single user environment but in the network it may troubles you
}
}end of the try
here next function is pointed
the starting that means records like 1,2,3… it points not 1 here which is the
first record instead it points nil like stack pointer if inserts then it points
the next empty location which is a new element is to be inserted basically
next() is implemented in this fashion is to implement error handling if a query
returns nil data then it will raise exception by placing the return of Boolean
value in the while statement but in this we cannot accesses the previous
records in the meanwhile already visited here the random access is not possible
when it reaches to the result set end the next() function returns the false
value
catch(Exception e)
{e.printStackTrace();}
}end of the main
}end of the class
//in
this program I am explaining about the prepared statement about the database connectivity in java
import java.sql.*;
import java.io.*;
class AlterDemo
{
public static void main(String
args[])
{
int r,s1,s2,s3;
String n;
try
{
Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
Connection
c=DriverManager.getConnection("Jdbc:Odbc:ramu1","scott","tiger");
PreparedStatement ps=c.prepareStatement("insert
into student values(?,?,?,?,?)");
DataInputStream k=new DataInputStream(System.in);
System.out.println("enter
the serial no");
r=Integer.parseInt(k.readLine());
ps.setInt(1,r);
System.out.println("enter the name to be
inserted");
n=k.readLine();
ps.setString(2,n);
System.out.println("enter the maths marks");
s1=Integer.parseInt(k.readLine());
ps.setInt(3,s1);
System.out.println("enter the physics marks");
s2=Integer.parseInt(k.readLine());
ps.setInt(4,s2);
System.out.println("enter the chemestry
marks");
s3=Integer.parseInt(k.readLine());
ps.setInt(5,s3);
ps.execute();
System.out.println(" row inserted
successfully");
}
catch(Exception e)
{
e.printStackTrace();
System.out.println("\n the exception raised");
}
}}
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