This Java code defines a DBTool class that provides a graphical user interface for interacting with a database. It uses Swing components like JComboBox and JLabels to display database metadata like users, schemas, tables and columns. When a user or table is selected, it queries the database and dynamically updates the other combo boxes with appropriate options based on the selection.

1. package com.nt.gui;
importjava.awt.BorderLayout;
importjava.awt.Color;
importjava.awt.FlowLayout;
importjava.awt.GridLayout;
importjava.awt.event.ActionEvent;
importjava.awt.event.ActionListener;
importjava.sql.Connection;
importjava.sql.DatabaseMetaData;
importjava.sql.DriverManager;
importjava.sql.ResultSet;
importjava.sql.ResultSetMetaData;
importjava.sql.SQLException;
importjava.sql.Statement;
importjavax.swing.JButton;
importjavax.swing.JComboBox;
importjavax.swing.JFrame;
importjavax.swing.JLabel;
importjavax.swing.JOptionPane;
importjavax.swing.JPanel;
importjavax.swing.JTextField;
publicclassDBTool extendsJFrame implementsActionListener{
private JLabel luser,ldb,ltable,lcolumn;
private JComboBox jcuser,jcdb,jctable,jccolumn;
//declaringothervariables..
private Connectioncon,con4;
private Statementst,st4,st5,st6;

2. private ResultSetrs,rs4,rs5,rs6;
//declaringmetadatavariables..
private ResultSetMetaDatarsmd;
private intcocnt1;
//constructorstarts
DBTool() throwsException
{
setTitle("MAGICALDATABASETOOL");
setSize(600,500);
setLocation(300,150);
setBackground(Color.WHITE);
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
setResizable(false);
//configuringthe containeritems throughJPanel
JPanel p=newJPanel();
setLayout(null);
add(p);
//settinggridlayout...
p.setLayout(newGridLayout(4,2,8, 8));
p.setBounds(70,65,400, 280);
luser=newJLabel("ALLUSERS/SCHEMAS");
p.add(luser);
jcuser=newJComboBox();
jcuser.addActionListener(this);
p.add(jcuser);
ldb=newJLabel("LOGICALNAME");
p.add(ldb);

3. jcdb=newJComboBox();
jcdb.addActionListener(this);
p.add(jcdb);
ltable=new JLabel("TABLENAME");
p.add(ltable);
jctable=newJComboBox();
jctable.addActionListener(this);
p.add(jctable);
lcolumn=newJLabel("COLUMN NAME");
p.add(lcolumn);
jccolumn=newJComboBox();
jccolumn.addActionListener(this);
p.add(jccolumn);
setVisible(true);
//registeringdriversandcreatingconnection
Class.forName("oracle.jdbc.driver.OracleDriver");
con = DriverManager.getConnection("jdbc:oracle:thin:@localhost:1521:orcl","system",
"password");
System.out.println(con.getClass().getName());
//creatingStatementobject
st = con.createStatement();
//gettingschemasandputtingincombobox 1
rs = st.executeQuery("selectusername fromdba_users");
int cnt1=0;
while (rs.next()) {
jcuser.addItem(rs.getString(1));
cnt1++;

4. }
System.out.println("Total noof Schemas: "+cnt1);
}//constructor
//mainmethod
publicstaticvoidmain(String[] args) throwsException{
newDBTool();
}//endmain
@Override
publicvoidactionPerformed(ActionEvente) {
if(jcuser==(JComboBox)e.getSource())
{//removingpreviousresults
jcdb.removeAllItems();
jctable.removeAllItems();
jccolumn.removeAllItems();
//gettingusertable selectedschemaitemintoone Objectvariable
Objectselected=jcuser.getSelectedItem();
try {
//generatingconditionthatif the selecteditemequalstothe url
if(selected.equals(selected)){
//gettingpasswordfromuseratrun time throughJOptionPane
StringinputValue =JOptionPane.showInputDialog(this,"PleaseEnterValidPassword");
//creatingnew Connectionw.r.t.targeturl andpassword
con4=DriverManager.getConnection("jdbc:oracle:thin:@localhost:1521:orcl",selected.toString(),inpu
tValue);
//gettinglogical DBname andputtingto combobox 2
st4 = con4.createStatement();

5. rs4 = st4.executeQuery("select*from global_name");
int cnt2=0;
while (rs4.next()) {
jcdb.addItem(rs4.getString(1));
cnt2++;
}
System.out.println("Total noof Logiacl Dbname: "+cnt2);
//gettingtable namesandputtingtocombobox 3
st5 = con4.createStatement();
rs5 = st5.executeQuery("selecttable_namefromtabs");
int cnt3=0;
while (rs5.next()) {
jctable.addItem(rs5.getString(1));
cnt3++;
}
System.out.println("Total noof Table Name: "+cnt3);
}//if
}//try
catch (Exceptione1) {e1.printStackTrace();}
}//outerif
//.................logicforgettingcolumnnamesfromjctable combobox ...................
if(jctable==(JComboBox)e.getSource())
{
//removingpreviousresults
jccolumn.removeAllItems();
//gettingcolumnnamesandputingtocombobox 4
try {
//preparationforgettingtable name atruntime

6. Strings=(String)jctable.getSelectedItem();
st6 = con4.createStatement();
Stringqry="select* from"+s;
//gettingresultsintoResultSet
rs6 = st6.executeQuery(qry);
//creatingMetaData obj
rsmd=rs6.getMetaData();
//gettingcolumncountinResultSetMetaData
int cocnt1=rsmd.getColumnCount();
int cnt=0;
//addingresultstocombobox 4
for(inti=1;i<=cocnt1;++i){
jccolumn.addItem(rsmd.getColumnLabel(i));
cnt++;
}
System.out.println("Total noof Columns: "+cnt);
}//try
catch (Exception e2) {e2.printStackTrace();}
}//if
}//actionPerformed()
}//class