There are numerous reasons why the compiler can't resolve a symbol -- you need to provide more info here. Maybe you could show us the exact error message. Or even show some of the code. Henry Books: Java Threads, 3rd Edition, Jini in a Nutshell, and Java Gems (contributor) John Pi...
Help me to resolve it. Caused by: java.sql.BatchUpdateException: Cannot add or update a child row: a foreign key constraint fails (`testdb`.`a_b`, CONSTRAINT `FK2E2EF2DEA3DDB7DE` FOREIGN KEY (`b_id`) REFERENCES `b` (`b_id`)) at com.mysql.jdbc.PreparedStatement.executeBatchSerially...