In order to interact with the database, it is necessary to install the correct driver, and to open a connection to the database.
The first step before writing the source code is to install a version of the JDBC PostgreSQL driver that is compatible with both: the used JDK version and the version of the database server.
The webpage at the hyperlink http://jdbc.postgresql.org/download.html shows the driver that is compatible with the used versions of PostgreSQL and JDK.
The driver can either be downloaded as a
.jar file, and then manually added to the class-path. Or, if a build tool like Maven or Gradle is used, it can be downloaded and installed automatically by adding the resource to the build-script ...