# IDEs and multiple JVMs

When you use an integrated development environment (IDE) to build a Java application, you can launch the application from within the IDE at any point in the development process. Typically, the IDE launches a JVM dedicated to the application. When the application completes, the JVM exits. Any database connections established by the application are closed.

During the development of a database application, most IDEs allow you to test individual database connections and queries without running the entire application. When you test an individual database connection or query (which requires a database connection), the IDE might launch a JVM that runs in a specialized testing environment. In this case, when a test completes, the JVM remains active and available for further testing, and the database connection established during the test remains open.

Because of the behaviors of the IDE described above, if you use the embedded Derby JDBC driver, you may encounter errors connecting in the following situations:

- You test an individual query or database connection and then try to run an application that uses the same database as the tested feature.

  The database connection established by testing the connection or query stays open, and prevents the application from establishing a connection to the same database.

- You run an application, and before it completes (for example, while it waits for user input), you attempt to run a second application or to test a connection or query that uses the same database as the first application.

Parent topic: Using Derby with IDEs