what exactly does this do Class.forName("com.mysql.jdbc.Driver").newInstance();

While connecting to MySQL database I do following steps

Connection con = null;
Resultset rs = null;
Statement st = null;
Class.forName("com.mysql.jdbc.Driver").newInstance();
con = DriverManager.getConnection("jdbc:mysql://localhost:3306/database","root","passwp");

Actually I wanted to know what does Class.forName("com.mysql.jdbc.Driver").newInstance(); statement do.

Althogh this class is not in mysql.jar. Where is it present?

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Answers:

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Method 1

The Class class is located in the java.lang package, so it is distributed with java, and imported automatically into every class.

What the forName() method does, is just return the Class object for the paramater that was loaded by the class loader. The newInstance() method then returns a new instance of the class.

So then what happens is you call
Class.forName(...)
it returns com.mysql.jdbc.Driver.class.
You then call newInstance() on that class which returns an instance of the class, whith no paramaters, so it’s basically calling new com.mysql.jdbc.Driver();.

Method 2

Quoting from the JDBC Specification, Chapter 9, Section 2:

JDBC drivers must implement the Driver interface, and the
implementation must contain a static initializer that will be called
when the driver is loaded. This initializer registers a new instance
of itself with the DriverManager.

And an example code is provided for AcmeJdbcDriver as follows:

public class AcmeJdbcDriver implements java.sql.Driver {
    static {
        java.sql.DriverManager.registerDriver(newAcmeJdbcDriver());
    }
}

And when you call Class.forName(String className), according to the API Documentation, the following happens:

A call to forName(“X”) causes the class named X to be initialized.

where initialization involves code in static block to be executed.

So basically, you initialize the Driver class, and in turn the class registers itself with the java.sql.DriverManager per the JDBC specification.

Please note, this is not needed anymore. Details can be found here.

The DriverManager methods getConnection and getDrivers have been
enhanced to support the Java Standard Edition Service Provider
mechanism. JDBC 4.0 Drivers must include the file
META-INF/services/java.sql.Driver. This file contains the name of the
JDBC drivers implementation of java.sql.Driver. For example, to load
the my.sql.Driver class, the META-INF/services/java.sql.Driver file
would contain the entry:
my.sql.Driver
Applications no longer need to explictly load JDBC drivers using
Class.forName().

Method 3

It initialize the class "com.mysql.jdbc.Driver" if found in the classpath, this imply that the driver is registered in the JDBC driver manager since the registration process is inside the static initializer of the driver class …

There is another approach you can use to register a driver : is to use the static DriverManager.registerDriver() method.

Method 4

It will create a new instance of the com.mysql.jdbc.Driver class and hence call the static initialization which will register the driver with the DriverManager so you can create mysql connections based on the URL you use in the second line.

The class however should be in the mysql.jar.

Method 5

It create a new instance of the com.mysql.jdbc.Driver class and Register the driver.

So then what happens is you call Class.forName(“com.mysql.jdbc.Driver”) without ‘newInstance()’ it returns com.mysql.jdbc.Driver class and register the driver only

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0

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