On calling JDBC update, the java program connects to the database server and executes the query. It means for each update, the java program contacts the database server and executes the query. Now, if we use JDBC batch-update, the java application needs to contact the database server only once and executes all the queries at the database server and returns to the java application.
In brief, it will reduce the round trip between java application and database server. Normally both will be on a different server, so it will reduce a lot of network resources. Hence, it achieves better performance.
