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Articles by Arushi
Page 7 of 9
Java ResultSet isBeforeFirst() method with example
When we execute certain SQL queries (SELECT query in general) they return tabular data.The java.sql.ResultSet interface represents such tabular data returned by the SQL statements.i.e. the ResultSet object holds the tabular data returned by the methods that execute the statements which quires the database (executeQuery() method of the Statement interface in general).The ResultSet object has a cursor/pointer which points to the current row. Initially this cursor is positioned before first row.The isBeforeFirst() method of the ResultSet interface is used to determine whether the cursor is at the default position of the ResultSet.rs.isBeforeFirst();This method returns an boolean this value is true, if the cursor is ...
Read MoreHow to retrieve the contents of a ResultSet from last to first in JDBC?
ResultSet objectCertain SQL queries (especially SELECT) returns tabular data, In JDBC the object of the java.sql.ResultSet interface holds the tabular data returned by the methods that execute the statements which quires the database (executeQuery() method of the Statement interface in general).ResultSet Cursor/pointerThe ResultSet object has a cursor/pointer which points to the current row. Initially this cursor is positioned before first row.There are two types of result sets namely, forward only and, bidirectional. By default the ResultSet we get by the executeQuery() method is of the type forward only. Using this you can traverse/move the cursor only forward direction.Bidirectional ResultSetA bi-directional ResultSet ...
Read MoreHow to get all table names from a database using JDBC?
You can get the list of tables in the current database in MySQL using the SHOW TABLES query.Show tables;Following JDBC program retrieves the list of tables in the database by executing the show tables query.Exampleimport java.sql.Connection; import java.sql.DriverManager; import java.sql.ResultSet; import java.sql.Statement; public class ListingTables { public static void main(String args[]) throws Exception { //Registering the Driver DriverManager.registerDriver(new com.mysql.jdbc.Driver()); //Getting the connection String mysqlUrl = "jdbc:mysql://localhost/mydatabase"; Connection con = DriverManager.getConnection(mysqlUrl, "root", "password"); System.out.println("Connection established......"); //Creating a Statement object ...
Read MoreHow to Maintain an open ResultSet after commit in JDBC?
ResultSet holdability determines whether the ResultSet objects (cursors) should be closed or held open when a transaction (that contains the said cursor/ ResultSet object) is committed using the commit() method of the Connection interface.ResultSet interface provides two values to specify the holdability namely CLOSE_CURSORS_AT_COMMIT and HOLD_CURSORS_OVER_COMMITIf the holdability of the ResultSet object is set to this value. Whenever you commit/save a transaction using the commit() method of the Connection interface, the ResultSet objects created in the current transaction (that are already opened) will be held open.Therefore, if you need to hold the ResultSet cursor open after the commit automatically, set ...
Read MoreHow to get the table name of the current ResultSet using JDBC?
You can get the name of the table in the current ResultSet object using the getTableName() method of the ResultSetMetaData interface. This method accepts an integer value representing the index of a column and, returns a String value representing the name of the table that contains the given column.Let us create a table with name MyPlayers in MySQL database using CREATE statement as shown below −CREATE TABLE MyPlayers( ID INT, First_Name VARCHAR(255), Last_Name VARCHAR(255), Date_Of_Birth date, Place_Of_Birth VARCHAR(255), Country VARCHAR(255), PRIMARY KEY (ID) );Now, we will insert 7 records in MyPlayers table using INSERT statements −insert into ...
Read MoreHow to get Row and Column Count from ResultSet in JDBC
Row countThe last() method of the ResultSet interface moves the cursor to the last row of the ResultSet and, the getRow() method returns the index/position of the current row.Therefore, to get the number of rows move the cursor to the last row using the last() method and get the position of that (last) row using the getRow() method.Let us create a table with name MyPlayers in MySQL database using CREATE statement as shown below −CREATE TABLE MyPlayers( ID INT, First_Name VARCHAR(255), Last_Name VARCHAR(255), Date_Of_Birth date, Place_Of_Birth VARCHAR(255), Country VARCHAR(255), PRIMARY KEY (ID) );Now, we will insert 7 records in ...
Read MoreHow to generate multiple insert queries via java?
JDBC provides a mechanism known as batch processing, in which you can group a set of INSERT or, UPDATE or, DELETE commands (those produce update count value) and execute them at once. You can insert multiple records in to a table using this.Adding statements to the batchStatement, PreparedStatement and CallableStatement objects hold a list (of commands) to which you can add related statements (those return update count value) using the addBatch() method.stmt.addBatch(insert1); stmt.addBatch(insert2); stmt.addBatch(insert3);Executing the batchAfter adding the required statements, you can execute a batch using the executeBatch() method of the Statement interface.stmt.executeBatch();Using batch updates, we can reduce the communication ...
Read MoreCollision-Free Protocols
In computer networks, when more than one station tries to transmit simultaneously via a shared channel, the transmitted data is garbled. This event is called collision. The Medium Access Control (MAC) layer of the OSI model is responsible for handling collision of frames. Collision – free protocols are devised so that collisions do not occur. Protocols like CSMA/CD and CSMA/CA nullifies the possibility of collisions once the transmission channel is acquired by any station. However, collision can still occur during the contention period if more than one stations starts to transmit at the same time. Collision – free protocols resolves ...
Read MoreHow to retrieve a record from an existing table in oracle database using JDBC API?
You can update/modify the existing contents of a record in a table using the UPDATE query. Using this you can update all the records of the table or specific records.SyntaxUPDATE table_name SET column1 = value1, column2 = value2...., columnN = valueN WHERE [condition];To update the contents of a record in a table using JDBC API you need to −Register the Driver: Register the driver class using the registerDriver() method of the DriverManager class. Pass the driver class name to it, as parameter.Establish a connection: Connect to the database using the getConnection() method of the DriverManager class. Passing URL (String), username (String), password (String) ...
Read MoreReservation Protocols in Computer Network
Reservation protocols are the class of protocols in which the stations wishing to transmit data broadcast themselves before actual transmission. These protocols operate in the medium access control (MAC) layer and transport layer of the OSI model.In these protocols, there is a contention period prior to transmission. In the contention period, each station broadcasts its desire for transmission. Once each station announces itself, one of them gets the desired network resources based upon any agreed criteria. Since each station has complete knowledge whether every other station wants to transmit or not before actual transmission, all possibilities of collisions are eliminated.Examples ...
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