Java Articles - Page 397 of 745

The difference between toArray() and toArray(T[] arr) is that both the methods returns an array containing all of the elements in this collection, but the latter has some additional features i.e. the runtime type of the returned array is that of the specified array.The syntax is as follows:public T[] toArray(T[] arr)Here, arr is the array into which the elements of this collection are to be stored, To work with the AbstractSequentialList class in Java, you need to import the following package:import java.util.AbstractSequentialList;The following is an example to implement AbstractSequentialList toArray() method in Java:Example Live Demoimport java.util.LinkedList; import java.util.AbstractSequentialList; public class ... Read More

You can add/set an auto increment constraint to a column in a table using the ALTER TABLE command.SyntaxALTER TABLE table_name ADD id INT PRIMARY KEY AUTO_INCREMENTAssume we have a table named Dispatches in the database with 7 columns namely id, CustomerName, DispatchDate, DeliveryTime, Price and, Location with description as shown below:+--------------+--------------+------+-----+---------+-------+ | Field        | Type         | Null | Key | Default | Extra | +--------------+--------------+------+-----+---------+-------+ | ProductName  | varchar(255) | YES  | UNI | NULL    | | | CustomerName | varchar(255) | YES  |     ... Read More

You can drop a constraint on a column of a table using the ALTER TABLE command.SyntaxALTER TABLE table_name DROP CONSTRAINT MyUniqueConstraint;Assume we have a table named Dispatches in the database with 7 columns namely id, CustomerName, DispatchDate, DeliveryTime, Price and, Location with description as shown below:+--------------+--------------+------+-----+---------+-------+ | Field        | Type         | Null | Key | Default | Extra | +--------------+--------------+------+-----+---------+-------+ | ProductName  | varchar(255) | YES  | UNI | NULL    | | | CustomerName | varchar(255) | YES  |     | NULL    | ... Read More

You can add a not null constraint to a column of a table using the ALTER TABLE command.SyntaxALTER TABLE table_name MODIFY column_name datatype NOT NULL;Assume we have a table named Dispatches in the database with 7 columns namely id, CustomerName, DispatchDate, DeliveryTime, Price and, Location with description as shown below:+--------------+--------------+------+-----+---------+-------+ | Field        | Type         | Null | Key | Default | Extra | +--------------+--------------+------+-----+---------+-------+ | ProductName  | varchar(255) | YES  |     | NULL    |       | | CustomerName | varchar(255) | YES  |     | NULL   ... Read More

You can add a unique constraint to a column using the ALTER TABLE commandSyntaxALTER TABLE table_name ADD CONSTRAINT MyUniqueConstraint UNIQUE(column1, column2...);Assume we have a table named Dispatches in the database with 7 columns namely id, CustomerName, DispatchDate, DeliveryTime, Price and, Location with description as shown below:+--------------+--------------+------+-----+---------+-------+ | Field        | Type         | Null | Key | Default | Extra | +--------------+--------------+------+-----+---------+-------+ | ProductName  | varchar(255) | YES  |     | NULL    | | | CustomerName | varchar(255) | No   |     | NULL ... Read More

You can add a primary key constraint to a column of a table using the ALTER TABLE command.SyntaxALTER TABLE table_name ADD CONSTRAINT MyPrimaryKey PRIMARY KEY (column1, column2...);Assume we have a table named Dispatches in the database with 7 columns namely id, CustomerName, DispatchDate, DeliveryTime, Price and, Location with description as shown below:+--------------+--------------+------+-----+---------+-------+ | Field        | Type         | Null | Key | Default | Extra | +--------------+--------------+------+-----+---------+-------+ | ProductName  | varchar(255) | YES  |     | NULL | | | CustomerName | varchar(255) | ... Read More

You can delete a column in a table using the ALTER TABLE command.SyntaxALTER TABLE table_name DROP COLUMN column_name;Assume we have a table named Sales in the database with 7 columns namely id, CustomerName, DispatchDate, DeliveryTime, Price and, Location as shown below:+----+-------------+--------------+--------------+--------------+-------+----------------+ | id | productname | CustomerName | DispatchDate | DeliveryTime | Price | Location     | +----+-------------+--------------+--------------+--------------+-------+----------------+ | 1  | Key-Board   | Raja         | 2019-09-01   | 08:51:36     | 7000  | Hyderabad      | | 2  | Earphones   | Roja         | 2019-05-01   ... Read More

You can change the datatype of a column in a table using the ALTER TABLE command.SyntaxALTER TABLE Sales MODIFY COLUMN column_name column_new_datatuypeAssume we have a table named Sales in the database with 7 columns namely ProductName, CustomerName, DispatchDate, DeliveryTime, Price, Location and, ID with description as:+--------------+--------------+------+-----+---------+-------+ | Field        | Type         | Null | Key | Default | Extra | +--------------+--------------+------+-----+---------+-------+ | ProductName  | varchar(255) | YES  |     | NULL | | | CustomerName | varchar(255) | YES  |     | NULL ... Read More

You can add a new column to a table using the ALTER TABLE command.SyntaxALTER TABLE table_name ADD column_name datatype;Assume we have a table named Sales in the database with 5 columns namely ProductName, CustomerName, DispatchDate, DeliveryTime, Price and, Location as shown below:+-------------+--------------+--------------+--------------+-------+----------------+ | ProductName | CustomerName | DispatchDate | DeliveryTime | Price | Location       | +-------------+--------------+--------------+--------------+-------+----------------+ | Key-Board   | Raja         | 2019-09-01   | 08:51:36     | 7000  | Hyderabad      | | Earphones   | Roja         | 2019-05-01   | 05:54:28     | 2000 ... Read More

The valueOf() method of the Date object accepts a String value representing a Date in JDBC escape format i.e. yyyy-mm-dd and converts the given String value into java.sql.Date object.Date date = Date.valueOf(“date_string”);Assume we have created a table named employee_data with the description as shown below:+----------+--------------+------+-----+---------+-------+ | Field    | Type         | Null | Key | Default | Extra | +----------+--------------+------+-----+---------+-------+ | id       | int(11)      | YES  |     | NULL    | | | Name     | varchar(255) | YES  |     ... Read More